Download Model DTC-500 - Lake Shore Cryotronics, Inc.

User’s Manual
Model DTC-500
Cryogenic Temperature
Indicator/Controller
Obsolete Notice:
This manual describes an obsolete Lake Shore product. This manual is a copy from our archives
and may not exactly match your instrument. Lake Shore assumes no responsibilityfor this manual
matching your exact hardware revision or operational procedures. Lake Shore is not responsible
for any repairs made to the instrument based on information from this manual.
Lake Shore Cryotronics, Inc.
575 McCorkle Blvd.
Westerville, Ohio 43082-8888USA
Internet Addresses:
[email protected]
[email protected]
Visit Our Website:
www.lakeshore.com
Fax: (614)891-1392
Telephone: (614)891-2243
Methods and apparatus disclosed and described herein have been developed solely on company funds of Lake Shore Cryotronics, Inc.
No government or other contractual support or relationship whatsoever has existed which in any way affects or mitigates proprietary
rights of Lake Shore Cryotronics, Inc. in these developments. Methods and apparatus disclosed herein may be subject to US. Patents
existing or applied for. Lake Shore Cryotronics, Inc. reserves the right to add, improve, modify, or withdraw functions, design
modifications, or products at any time without notice. Lake Shore shall not be liable for errors contained herein or for incidental or
consequentialdamages in connection with furnishing, performance, or use of this material.
Obsolete Manual
1974
Table o f Contents
Section
I.
II.
III.
IV.
V.
General Information
1.1 I n t r o d u c t i o n
1 . 2 Description
1 . 3 General S p e c i f i c a t i o n s
1 . 4 Major Assemblies Supplied
1 . 5 Accessory Equipment and Custom Options
1
1
2
3
3
Installation
2.1 Introduction
2.2 I n i t i a l I n s p e c t i o n
2 . 3 Power Requirements
2.4 Grounding Requirements
2.5 I n s t a l l a t i o n
2.6 Repackaging f o r Shipment
5
5
5
5
7
7
Operation I n s t r u c t i o n s
3.1 I n t r o d u c t i o n
3.2 C o n t r o l s , I n d i c a t o r s and Connectors
3 . 3 I n i t i a l Checks
3.4 Temperature Readout Mode
3.5 Constant Temperature Control Mode
3.6 Manual Reset Heating Mode
3.7 Temperature Readout Mode (Sensor B)
3.8 Remote Temperature Programming
3.9 Grounding
9
9
13
13
16
17
17
18
21
Theory o f O p e r a t i o n
4.1 I n t r o d u c t i o n
4.2 General D e s c r i p t i o n
4 . 3 D e t a i l e d Description/Regulated Power S u p p l i e s
( a ) Reference Current
(b) Diode Constant Current Supply
( c ) S e t P o i n t Voltage Supply and D i v i d e r
(d) Amplifier Supply Voltages
(e) V a r i a b l e Gain A m p l i f i e r
( f ) Automatic Reset C i r c u i t , Rounding C i r c u i t
(g) Output Power A m p l i f i e r
(h) Manual H e a t e r Current Control
( i ) H e a t e r Current Metering and Limiting
22
22
24
24
24
24
24
24
25
25
26
26
Maintenance and Trouble Shooting
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
VI.
Page
Introduction
T e s t Equipment and Accessories
General Remarks
S e r v i c i n g P r i n t e d C i r c u i t Boards
O p e r a t i o n a l Checks
Normal O p e r a t i n g Voltages and Gains
C a l i b r a t i o n of S e t P o i n t Voltage
C a l i b r a t i o n of S e n s o r Current
Parts List, P r i n t e d C i r c u i t Board Component
Locator and Schematic
Appendixes
27
27
27
28
28
29
30
30
31
37
i
Table of I l l u s t r a t i o n s
Reference D e s c r i p t i o n
Page
Figure 1.1
Model DTC-500 Cryogenic
Temperature I n d i c a t o r / C o n t r o l l e r
Figure 2.1
Sensor and Heater Cables
6
Table 3.1
E n t r y Number C o r r e l a t i o n
9 , 10
Figure 3.1
Front Panel
11
Figure 3.2
Rear Panel
12
Figure 3 . 3
Block Diagram, DTC-500
Temperature C o n t r o l l e r
14
Figure 3.4
Temperature v e r s u s Time
Characteristics of Controller
15
Figure 3.5
Remote Temperature Programming
18
Figure 3 . 6
Programming Networks
19
Figure 3 . 7
Programmer Voltage
20
Figure 4.1
S i m p l i f i e d Equivalent C i r c u i t
o f Automatic Reset Amplifier
23
Table 5.1
Parts L i s t
Figure 5 . 1
C i r c u i t Schematic Diagram
35
Figure 5.2
P r i n t e d C i r c u i t Board
Component Diagram
36
iv
31-34
ii
iv
SECTION I
General Information
1.1
Introduction
T h i s s e c t i o n c o n t a i n s a d e s c r i p t i o n of t h e Model DTC-500 Cryogenic
Temperature C o n t r o l l e r , i t s a p p l i c a t i o n s , g e n e r a l s p e c i f i c a t i o n s , major
assemblies s u p p l i e d and a c c e s s o r y equipment a v a i l a b l e .
1.2
D e s c r i p t i o n and A p p l i c a t i o n s
The Model DTC-500 Cryogenic Temperature C o n t r o l l e r i s housed i n an
aluminum case w i t h s t a n d a r d 19" r e l a y p a n e l f r o n t f o r rack mounting. A l l
connections are a t t h e rear o f t h e case w i t h a l l normal o p e r a t i n g c o n t r o l s
on t h e f r o n t p a n e l . The i n s t r u m e n t is l i n e o p e r a t e d from e i t h e r 115 v o l t
o r 230 v o l t mains, 50 o r 60 H e r t z .
The c o n t r o l l e r is designed t o a c c e p t a v o l t a g e s i g n a l from a temperature
s e n s i t i v e t r a n s d u c e r ( g e n e r a l l y a DT-500 o r TG-100 Diode which i s n o t s u p p l i e d ) ,
compare t h i s s i g n a l w i t h an i n t e r n a l set p o i n t v o l t a g e , amplify and p r o c e s s
t h e i r d i f f e r e n c e ( e r r o r s i g n a l ) , and d r i v e an e x t e r n a l h e a t i n g element. An
i n t e r n a l p r e c i s i o n 10 microampere c o n s t a n t c u r r e n t s o u r c e i s provided t o
e x c i t e t h e temperature transducer.
The e r r o r p r o c e s s i n g s e c t i o n o f t h e c o n t r o l l e r i s o f t h e p r o p o r t i o n a l
p l u s i n t e g r a l mode d e s i g n . Generous a m p l i f i e r g a i n ranges have been provided
t o a f f e c t r a p i d c l o s e d loop response times, low s t e a d y s t a t e temperature
o f f s e t s and t o i n s u r e system s t a b i l i t y o v e r a wide range of thermal system
parameters.
The o u t p u t power a m p l i f i e r is c a p a b l e of s u p p l y i n g up t o 10 Watts o f h e a t e r
power. I n view o f t h e high c o s t o f some c r y o g e n i c f l u i d s such as helium,
c o s t consciousness s u g g e s t s t h a t c r y o s t a t d e s i g n and o p e r a t i n g s t r a t e g i e s
be planned t o l i m i t h e a t e r power requirements t o s u b s t a n t i a l l y less t h a n
t e n watts. Power b o o s t e r s are a v a i l a b l e from t h e company as a c c e s s o r y
equipment i f r e q u i r e d f o r s p e c i a l a p p l i c a t i o n s .
The p r i n c i p a l i n t e n d e d a p p l i c a t i o n o f t h e DTC-500 C o n t r o l l e r is as a
c o n s t a n t temperature r e g u l a t o r f o r l a b o r a t o r y size c r y o s t a t s . I t s b a s i c
d e s i g n , however, e n a b l e s i t t o be used as a g e n e r a l purpose c o n t r o l l e r f o r
s e n s o r s whose raw o u t p u t s range between 0 and 3 . 0 v o l t s and whose incremental
s e n s i t i v i t i e s are i n t h e range o f t e n t h s o f m i l l i v o l t s .
I n a d d i t i o n t o i t s u s e as a c l o s e d loop automatic t e m p e r a t u r e c o n t r o l l e r ,
t h e Model DTC-500 C o n t r o l l e r may be used as a p r e c i s i o n thermometer. By
a d j u s t i n g t h e set p o i n t v o l t a g e s o t h a t t h e e r r o r s i g n a l (as i n d i c a t e d by t h e
n u l l meter) i s z e r o , t h e o u t p u t v o l t a g e of t h e temperature s e n s o r i s a c c u r a t e l y
obtained. Reference t o a v o l t a g e v e r s u s t e m p e r a t u r e c a l i b r a t i o n curve f o r
t h e t r a n s d u c e r i n use w i l l t h e n g i v e i t s t e m p e r a t u r e ,
1
1.3
General S p e c i f i c a t i o n s
The f o l l o w i n g s p e c i f i c a t i o n s f o r t h e DTC-500 C o n t r o l l e r a r e a p p l i c a b l e
when used w i t h t h e TG-100 o r DT-500 f u l l range t e m p e r a t u r e s e n s i t i v e d i o d e .
General :
C o n t r o l l e r Range
-
1°K t o 400°K nominal
H e a t e r Output
-
10-3 t o
Sensor
-
Models TG-100 o r DT-500, t e m p e r a t u r e
s e n s i t i v e d i o d e s , single-ended o r
f l o a t i n g model
Sensor I n p u t
-
Four t e r m i n a l c o n n e c t i o n , c o n s t a n t
current, potentiometric
Sensor Current
-
10 microamperes
I n p u t Line Voltage
-
ll5V o r 230V, 50-60 Hz
Power Consumption
-
30VA
C i r c u i t design
-
Solid S t a t e
15 pounds
Dimensions
-
Sensitivity
-
~1 Amp/millivolt i n t o 10 ohm r e s i s t o r
at maximum s e t t i n g
-
0 t o 3.0 v o l t s
Switch - 1 v o l t p e r s t e p , 100 mV p e r
Weight
10 watts, 0-1 Amp, 0-10 Volts
5¼' h i g h , 19" wide,
mounting
11½ deep, rack
Temperature C o n t r o l :
Set Points
s t e p , and 10 t u r n i n t e r p o l a t i n g
p o t e n t i o m e t e r with 0.2 mV g r a d u a t i o n s ,
0.1% l i n e a r i t y
Repeatability
-
±100 m i c r o v o l t s (For a DT-500 a t 4.2 K
t h i s r e p r e s e n t s 0.001 K )
Automatic Reset
-
3 t o 100 second v a r i a b l e t i m e
constant, o r o f f
2
Manual Output Control Range
-
10 t u r n potentiometer c o n t r o l ,
0 t o f u l l current
Full Scale Heater
Current Ranges
-
1 0 mA, 30 mA, 100 mA, 300 mA, 1 A
Heater R e s i s t a n c e f o r
Max Power
-
10 Ohms
C o n t r o l l e r P r o p o r t i o n a l Gain
-
1 Amp/mV i n a u t o m a t i c mode
(nomina 1)
Temperature Readout :
(2 Sensor c o n n e c t i o n s , f r o n t p a n e l s e l e c t a b l e between c o n t r o l
s e n s o r and t e m p e r a t u r e s e n s i n g o n l y s e n s o r )
1.4
Accuracy
-
150 m i c r o v o l t s 2100 m i c r o v o l t s
± calibration error of sensor
E x c i t a t i o n Current
-
1 0 microamperes ±0.1%
E x c i t a t i o n Current Regulation
-
0.05%
S e n s o r C a l i b r a t i o n Chart
-
Must b e s u p p l i e d by manufacturer
o f s e n s o r i n use.
Major Assemblies S u p p l i e d
The Model DTC-500 Cryogenic Temperature C o n t r o l l e r i n c l u d e s as s t a n d a r d
equipment, i n a d d i t i o n t o t h e c o n t r o l l e r p r o p e r , t h e f o l l o w i n g a d d i t i o n a l
components :
(1)
1, O p e r a t i n g and S e r v i c e Manual
(2)
2 , Five p i n p l u g s f o r t e m p e r a t u r e s e n s o r c a b l e s
(3)
1, Seven p i n p l u g f o r remote s e t p o i n t c a b l e
Temperature s e n s i t i v e d i o d e s are n o t s u p p l i e d as p a r t o f t h e DTC-500
Controller.
1.5
Accessory Equipment and Custom Options A v a i l a b l e
The f o l l o w i n g a c c e s s o r y equipment and custom o p t i o n s a r e a v a i l a b l e from
t h e f a c t o r y . Items marked w i t h an a s t e r i s k (*) are o f a custom n a t u r e . The
customer should d i s c u s s t h e s e items w i t h a f a c t o r y r e p r e s e n t a t i v e b e f o r e
ordering.
(1)
Estra 5 and 7 p i n c o n n e c t o r s .
3
(2)
M u l t i s e n s o r s e l e c t o r p a n e l . ( S p e c i a l low thermal o f f s e t s w i t c h
and c a b l i n g f o r s e l e c t i n g among m u l t i p l e s e n s o r s . ) *
(3)
Remote s e t p o i n t v o l t a g e c o n t r o l and programming module.*
(4) Custom m o d i f i c a t i o n o f s e n s o r c u r r e n t supply v a l u e . *
(5)
TG-100 Gallium Arsenide o r DT-500 S i l i c o n Temperature S e n s i t i v e
Diode ( U n c a l i b r a t e d ) .
(See d a t a s h e e t s a t end o f t h i s manual f o r
nominal o p e r a t i n g c h a r a c t e r i s t i c s and c a s e s t y l e s a v a i l a b l e . )
(6)
TG-100 Gallium Arsenide o r DT-500 S i l i c o n Temperature S e n s i t i v e
Diode, ( C a l i b r a t e d ) . S t a n d a r d s l a b o r a t o r y c a l i b r a t i o n s e r v i c e f o r
c o r r e l a t i n g d i o d e o u t p u t v o l t a g e w i t h d i o d e t e m p e r a t u r e . See
sensor d a t a s h e e t f o r a d d i t i o n a l information.
(7)
Power Boosters f o r h e a t e r power requirements i n excess o f t e n
watts, o r o t h e r t h a n t e n ohm h e a t e r r e s i s t a n c e s .
4
SECTION I I
Installation
2.1
Introduction
This s e c t i o n c o n t a i n s i n f o r m a t i o n and i n s t r u c t i o n s n e c e s s a r y f o r
t h e i n s t a l l a t i o n and s h i p p i n g of t h e Model DTC-500 Cryogenic Temperature
C o n t r o l l e r . Included a r e i n i t i a l i n s p e c t i o n i n s t r u c t i o n s , power and
grounding r e q u i r e m e n t s , i n s t a l l a t i o n i n f o r m a t i o n and i n s t r u c t i o n s f o r
repackaging f o r shipment.
2.2
I n i t i a l Inspection
T h i s i n s t r u m e n t was e l e c t r i c a l l y and mechanically i n s p e c t e d p r i o r t o
shipment. I t should be f r e e from mechanical damages, and i n p e r f e c t working
o r d e r upon r e c e i p t . To confirm t h i s , t h e i n s t r u m e n t should b e i n s p e c t e d
v i s u a l l y f o r obvious damage upon r e c e i p t and t e s t e d e l e c t r i c a l l y by u s e t o
d e t e c t any concealed damage. Be s u r e t o i n v e n t o r y a l l components s u p p l i e d
b e f o r e d i s c a r d i n g any s h i p p i n g materials. I f t h e r e i s damage t o t h e instrument
i n t r a n s i t , b e s u r e t o f i l e a p p r o p r i a t e claims w i t h t h e c a r r i e r , and/or
i n s u r a n c e company. Please a d v i s e t h e company of such f i l i n g s . In case o f
p a r t s s h o r t a g e s , p l e a s e a d v i s e t h e company. The s t a n d a r d Lake Shore C r y o t r o n i c s
warranty is given on page i i .
2.3
Power Requirements
Before c o n n e c t i n g t h e power c a b l e t o t h e l i n e , a s c e r t a i n t h a t t h e l i n e
v o l t a g e s e l e c t o r s w i t c h (115V o r 230V) i s i n t h e a p p r o p r i a t e p o s i t i o n f o r
t h e l i n e v o l t a g e t o b e used. Examine t h e power l i n e f u s e , FU1, (Key No. 14,
Page 12) t o i n s u r e t h a t it i s a p p r o p r i a t e f o r t h e l i n e v o l t a g e . (115V = 0.25
Amp, 230V = 0.15 Amp) Nominal p e r m i s s i b l e l i n e v o l t a g e f l u c t u a t i o n i s
±10% a t 50 t o 60 Hz.
Caution: Disconnect l i n e cord b e f o r e
i n s p e c t i n g o r changing l i n e f u s e .
2.4
Grounding Requirements
To p r o t e c t o p e r a t i n g p e r s o n n e l , t h e N a t i o n a l E l e c t r i c a l Manufacturers '
A s s o c i a t i o n (NEMA) recommends and some l o c a l codes r e q u i r e i n s t r u m e n t p a n e l s
and c a b i n e t s t o b e grounded. This instrument i s equipped w i t h a t h r e e - c o n d u c t o r
power c a b l e which, when plugged i n t o an a p p r o p r i a t e r e c e p t a c l e , grounds t h e
instrument.
5
FIGURE 2.1
SENSOR AND HEATER CABLES
2.5
Installation
The DTC-500 C o n t r o l l e r is a l l s o l i d s t a t e and does n o t g e n e r a t e
s i g n i f i c a n t h e a t . I t may t h e r e f o r e b e rack mounted i n c l o s e proximity
t o o t h e r equipment i n dead a i r s p a c e s . However, t h e h e a t from such a d j a c e n t
equipment should n o t s u b j e c t t h e DTC-500 C o n t r o l l e r t o an ambient temperature
i n e x c e s s of 5O°C (122°F). A s w i t h any p r e c i s i o n i n s t r u m e n t , it should n o t
b e s u b j e c t e d t o t h e shock and v i b r a t i o n s which u s u a l l y accompany h i g h vacuum
pumping systems.
The recommended c a b l e diagrams f o r t h e s e n s o r d i o d e and h e a t e r element
are given i n Figure 2.1 (a) and (b)
The u s e of a f o u r wire diode connection
i s h i g h l y recommended t o avoid i n t r o d u c i n g l e a d I R drops i n t h e v o l t a g e
s e n s i n g p a i r . The i n d i c a t e d s h i e l d i n g connections are t h e recommended s t a n d a r d
p r a c t i c e t o avoid ground l o o p s . The alternate w i r i n g scheme shown i n Fig. 2 . 1
(c) may b e used f o r t h e d i o d e , i n less c r i t i c a l a p p l i c a t i o n s .
.
The h e a t i n g element should b e f l o a t e d t o p r e c l u d e t h e p o s s i b i l i t y o f any
of t h e h e a t e r c u r r e n t b e i n g conducted i n t o t h e d i o d e s e n s o r l e a d s . Electrical
feedback i n a d d i t i o n t o t h e d e s i r e d thermal feedback, may cause o s c i l l a t i o n s
and c e r t a i n l y erroneous t e m p e r a t u r e r e a d i n g s .
I n s p e c t t h e h e a t e r element f u s e FU2, (Key No. 16, Pg. 12) f o r p r o p e r v a l u e .
( 3 AG, 1.0A, Slow Blow, o r smaller c u r r e n t r a t i n g i f d e s i r e d . ) T h i s f u s e p r o t e c t s
t h e o u t p u t a m p l i f i e r from damage i n case of h e a t e r element s h o r t i n g . Use o f a
l a r g e r f u s e may c a u s e damage t o t h e instrument and i n v a l i d a t e s t h e i n s t r u m e n t
warranty.
2.6
Repackaging f o r Shipment
Before r e t u r n i n g an i n s t r u m e n t t o t h e f a c t o r y f o r r e p a i r , p l e a s e d i s c u s s
t h e malfunction w i t h a f a c t o r y r e p r e s e n t a t i v e . He may be a b l e t o s u g g e s t
s e v e r a l f i e l d tests which w i l l p r e c l u d e r e t u r n i n g a s a t i s f a c t o r y instrument
t o t h e f a c t o r y when t h e malfunction is elsewhere. If it i s i n d i c a t e d t h a t
t h e f a u l t i s i n t h e i n s t r u m e n t a f t e r t h e s e tests, t h e r e p r e s e n t a t i v e w i l l send
s h i p p i n g i n s t r u c t i o n s and l a b e l s f o r r e t u r n i n g i t .
When r e t u r n i n g an i n s t r u m e n t , p l e a s e a t t a c h a t a g s e c u r e l y t o t h e
i n s t r u m e n t i t s e l f (not on t h e s h i p p i n g c a r t o n ) c l e a r l y s t a t i n g :
(1)
Owner and a d d r e s s
(2)
Instrument Model and S e r i a l Number
(3)
Malfunction symptoms
(4)
D e s c r i p t i o n o f e x t e r n a l connections and c r y o s t a t s .
I f t h e o r i g i n a l c a r t o n i s a v a i l a b l e , repack t h e i n s t r u m e n t i n p l a s t i c bag,
p l a c e i n c a r t o n u s i n g o r i g i n a l s p a c e r s t o p r o t e c t p r o t r u d i n g c o n t r o l s , and
c l o s e c a r t o n . S e a l l i d w i t h p a p e r o r nylon t a p e . A f f i x m a i l i n g l a b e l s and
"FRAGILE" warnings.
7
I f t h e o r i g i n a l c a r t o n i s n o t a v a i l a b l e , wrap t h e i n s t r u m e n t i n
p r o t e c t i v e p l a s t i c wrapping m a t e r i a l b e f o r e p l a c i n g i n an i n n e r c o n t a i n e r .
Place shock a b s o r b i n g material around a l l s i d e s of t h e i n s t r u m e n t t o p r e v e n t
damage t o p r o t r u d i n g c o n t r o l s . P l a c e t h e i n n e r c o n t a i n e r i n a second
heavy c a r t o n and s e a l w i t h t a p e . A f f i x m a i l i n g l a b e l s and "FRAGILE" warnings.
SECTION III
Operating I n s t r u c t i o n s
3.1
Introduction
T h i s s e c t i o n c o n t a i n s a d e s c r i p t i o n of t h e o p e r a t i n g c o n t r o l s , t h e i r
adjustment under normal o p e r a t i n g c o n d i t i o n s , t y p i c a l c o n t r o l l e r a p p l i c a t i o n s
and suggested c r y o s t a t adjustment t e c h n i q u e s . These i n s t r u c t i o n s a r e
p r e d i c a t e d upon t h e i n s t r u m e n t having been i n s t a l l e d as o u t l i n e d i n S e c t i o n II.
The diode p o l a r i t y as shown i n Fig. 2.1 (a) i n p a r t i c u l a r must be c o r r e c t .
A c a l i b r a t e d diode i s assumed t o b e connected, as shown i n Fig. 2.1 ( a ) , t o
t h e "Sensor A" r e c e p t a c l e and a 10 ohm h e a t i n g element i s assumed t o be
connected t o t h e "Heater" t e r m i n a l s as shown i n Fig. 2 . 1 ( b ) .
C o n t r o l s , I n d i c a t o r s and Connectors
3.2
The o p e r a t i n g c o n t r o l s , i n d i c a t o r s and connectors on t h e i n s t r u m e n t ' s
f r o n t and rear p a n e l s are shown i n Figures 3.1 and 3.2. The numbers w i t h
l e a d e r s t o v a r i o u s c o n t r o l s i n t h e f i g u r e s are keyed t o t h e entries i n
Table 3.1.
-
Table 3.1
NO. KEY
1
FUNCTION
NAME
SET POINT
0
2
Entry Number C o r r e l a t i o n
-
-
VOLTS
0.1
SET POINT - VOLTS
0, 1 and 2 VOLTS
-
Ten t u r n v e r n i e r i n t e r p o l a t o r
potentiometer t o continously a d j u s t
set p o i n t v o l t a g e between switch
s e t t i n g and n e x t h i g h e r s e t t i n g .
S e l e c t o r s w i t c h o f Kelvin-Varley
d i v i d e r , 1.0 v o l t s t e p s .
S e l e c t o r switch o f Kelvin-Varley
d i v i d e r , 0.1 v o l t p e r s t e p .
3
SET POINT
VOLTS
0 t o .9 VOLTS
4
GAIN 1
5
AUTO- RESET
OFF, M I N . - MAX.
Adjusts a u t o - r e s e t time c o n s t a n t
of i n t e g r a t o r . (See F i g . 3.3)
E f f e c t i v e l y determines time
c o n s t a n t of i n t e g r a t o r between
100 and 3 seconds, "MIN." and "MAX."
respectively.
6
AUTO A, MAN. A,
MAN. B.
Mode s e l e c t o r s w i t c h : AUTO A u s e s
sensor A t o automatically control
temperature. MAN. A disengages
automatic c o n t r o l f e a t u r e b u t p e r m i t s
r e a d o u t of s e n s o r A v o l t a g e . MAN. B
p e r m i t s readout of s e n s o r B v o l t a g e .
-
100
Adjusts o v e r a l l c o n t r o l l e r gain
between 100 and 10,000 (Figure 3.3)
9
Table 3.1 ( c o n t . )
NAME
FUNCTION
7
MAN. RESET
When mode s e l e c t o r switch ( 5 ) i s i n
e i t h e r MAN. A o r MAN. B p o s i t i o n , t h e
MAN. RESET t e n t u r n p o t e n t i o m e t e r
p e r m i t s t h e u s e r t o manually a d j u s t
t h e c u r r e n t t o t h e h e a t e r element.
(Caution: High s e t t i n g s w i l l q u i c k l y
b o i l away cryogenic f l u i d s ) .
8
MAX. HEATER-AMP.
Switch s e l e c t e d c u r r e n t limiter. Use
of a low s e t t i n g w i l l avoid i n a d v e r t e n t
b o i l - o f f i n s e t t i n g up system,
and/or system o s c i l l a t i o n s .
9
POWER
A. C. l i n e s w i t c h (ON/OFF)
10
NO LABEL
A. C. l i n e p i l o t l i g h t
11
HEATER CURRENT
Meters h e a t e r element c u r r e n t . F u l l
scale d e f l e c t i o n corresponds t o MAX.
NO. KEY
HEATER-AMP.
switch (8) s e t t i n g .
12
NULL
I n d i c a t e s t h e d i f f e r e n c e between
t h e set p o i n t v o l t a g e and t h e s e n s o r
o u t p u t v o l t a g e . Meter is n o n - l i n e a r
f o r large e r r o r s o f e i t h e r s i g n .
13
115/230V
50-60 HZ
A. C. l i n e v o l t a g e s e l e c t o r s l i d e
switch
14
¼A S. B.
A. C. l i n e f u s e (FUl).
15
NO LABEL
A. C. l i n e cord
16
1.0A, S. B.
Heater element l i n e f u s e , 1 AMP.,
Slow Blow
17
SENSOR A
Sensor A c a b l e r e c e p t a c l e . (Five p i n ,
Amphenol t y p e 126-217 Plug)
18
SENSOR B
(Five p i n ,
Sensor B c a b l e r e c e p t a c l e .
Amphenol t y p e 126-217 Plug)
19
TEMP. SET POINT
INTERNAL, REMOTE
S e l e c t s between i n t e r n a l s e t p o i n t
v o l t a g e d i v i d e r and external d i v i d e r
f o r comparison with s e n s o r v o l t a g e .
Front p a n e l set p o i n t c o n t r o l s i n o p e r a t i v e when switch i s i n t h e
"REMOTE" p o s i t i o n . Be s u r e t h i s c o n t r o l
i s s e t on "INTERNAL" s i n c e i t s
l o c a t i o n on t h e r e a r p a n e l may cause
one t o overlook i t s s e t t i n g when
i n i t i a l l y checking o u t t h e i n s t r u m e n t .
See p a r a . 2 . 3
10
11
12
Table 3.1
NO. KEY
(cont.)
NAME
FUNCTION
20
NO LABEL
Remote s e t p o i n t v o l t a g e d i v i d e r
c a b l e r e c e p t a c l e (Amphenol 126-195
Plug)
21
HEATER
Heater element l e a d t e r m i n a l s
(Grey i s t h e high s i d e and Black
i s t h e low s i d e ) .
22
GROUND
Chassis ground t e r m i n a l
3.3
I n i t i a l Checks
I n i t i a l checks, c a l i b r a t i o n checks, and s e r v i c i n g p r o c e d u r e s a r e
d e s c r i b e d i n S e c t i o n V, MAINTENANCE.
3.4
Temperature Readout Mode
To u s e t h e DTC-500 a s a cryogenic thermometer t o measure t h e t e m p e r a t u r e
o f a c a l i b r a t e d d i o d e connected t o SENSOR A t e r m i n a l s , i n i t i a l l y p o s i t i o n
s w i t c h e s and c o n t r o l s as f o l l o w s :
(1)
Temperature s e t p o i n t switch (Key No. 19) t o "INTERNAL".
(2)
Mode s w i t c h (Key No. 6) t o "MAN.
(3)
"MAN.
(4)
"MAX. HEATER-AMP."
(5)
"GAIN"
(6)
"AUTO RESET" (Key No. 5) t o o f f .
(7)
"POWER"
A".
RESET" (Key No. 7 ) t o zero.
(Key No. 8) t o 0.01.
(Key No. 4 ) t o minimum s e t t i n g .
s w i t c h (Key No. 9) t o on.
The n u l l meter w i l l probably d e f l e c t o f f s c a l e ( e i t h e r l e f t o r r i g h t )
when t h e power s w i t c h i s t u r n e d on. I f t h e d e f l e c t i o n i s t o t h e l e f t , t h e
s e t p o i n t v o l t a g e i s l e s s t h a n t h e s e n s o r v o l t a g e , If t h e d e f l e c t i o n is t o t h e
r i g h t , t h e s e t p o i n t voltage i s g r e a t e r than t h e sensor voltage.
Adjust t h e s e t p o i n t v o l t a g e u n t i l t h e "NULL" meter i s c e n t e r e d w h i l e
i n c r e a s i n g t h e "GAIN" towards maximum. I n c r e a s i n g t h e v o l t a g e w i l l move t h e meter
p o i n t e r t o t h e r i g h t ; d e c r e a s i n g t h e s e t p o i n t v o l t a g e w i l l d e f l e c t t h e meter
p o i n t e r t o t h e l e f t . A f t e r c e n t e r i n g t h e meter, r e a d t h e s e t p o i n t v o l t a g e by
adding t h e v e r n i e r p o t e n t i o m e t e r r e a d i n g (approximately s c a l e d ) t o t h e "SET POINT"
s w i t c h s e t t i n g v a l u e . The t e n t u r n d i a l ' s 500 d i v i s i o n s correspond t o 100 m i l l i v o l t s , s o t h a t each d i a l d i v i s i o n corresponds t o 0.2 m i l l i v o l t s , r e a d a b l e t o
0.1 m i l l i v o l t .
13
14
FIGURE 3.4
TEMPERATURE VERSUS TIME
CHARACTERISTICS OF CONTROLLER
15
After determining t h e set p o i n t v o l t a g e , refer t o t h e d i o d e c a l i b r a t i o n
c h a r t t o a s c e r t a i n t h e diode temperature.
3.5
Constant Temperature Control Mode
Assume t h a t a c a l i b r a t e d d i o d e i s i n u s e as d e s c r i b e d i n paragraph
3 . 4 . To m a i n t a i n a c o n s t a n t t e m p e r a t u r e , determine t h e corresponding s e t
p o i n t v o l t a g e from t h e diode c a l i b r a t i o n c h a r t . S e t t h i s v o l t a g e on t h e
"SET POINT" s w i t c h and v e r n i e r .
P o s i t i o n c o n t r o l s as i n d i c a t e d below:
(1)
Temperature s e t p o i n t s w i t c h (Key No. 19) t o "INTERNAL."
(2)
Mode s w i t c h (Key No. 6) t o "AUTO A."
(3)
"MAN.
RESET" (Key No. 7 ) t o zero.
(4)
"MAX.
HEATER-AMP"
(5)
"GAIN"
(6)
"AUTO RESET" (Key No. 5) t o o f f .
(7)
"SET POINT VOLTS" s w i t c h and p o t e n t i o m e t e r t o v o l t a g e corresponding
t o desired temperature.
(8)
"POWER"
(Key No. 8) t o 1.0 AMP.
(Key No. 4) t o minimum s e t t i n g .
s w i t c h (Key No. 9) t o on.
I f t h e block o r sample h o l d e r whose t e m p e r a t u r e i s t o b e c o n t r o l l e d i s
c o l d e r t h a n t h e set p o i n t t e m p e r a t u r e , t h e s e n s o r d i o d e v o l t a g e w i l l b e high
and t h e n u l l meter w i l l d e f l e c t t o t h e l e f t . Slowly i n c r e a s e t h e "GAIN"
s e t t i n g (Key No. 4) i n a clockwise d i r e c t i o n . The "HEATER CURRENT" meter
should show an immediate up scale d e f l e c t i o n p r o p o r t i o n a l t o t h e "GAIN"
s e t t i n g . The "NULL" meter should start t o come o f f i t s f u l l l e f t d e f l e c t i o n
p o s i t i o n as t h e gain i s i n c r e a s e d . A s t h e sample h o l d e r t e m p e r a t u r e approaches
t h e set p o i n t t e m p e r a t u r e , t h e NULL meter w i l l approach c e n t e r s c a l e and t h e
"HEATER CURRENT'' meter w i l l assume a s t e a d y v a l u e even with a f u r t h e r i n c r e a s e
i n t h e g a i n s e t t i n g , Continue t o i n c r e a s e t h e g a i n u n t i l an incremental change
i n g a i n produces a n e g l i g i b l e r e d u c t i o n i n t h e n u l l e r r o r , b u t n o t s o high as t o
produce o s c i l l a t i o n s .
To f u r t h e r reduce t h e n u l l e r r o r , r o t a t e t h e "AUTO RESET" g a i n c o n t r o l
(Key No. 5) o u t o f t h e d e t e n t ( o f f ) p o s i t i o n i n t h e clockwise d i r e c t i o n . A s
t h e c o n t r o l i s advanced, t h e n u l l meter should approach t h e c e n t e r p o s i t i o n
w i t h unobservable e r r o r . Leave t h e "AUTO RESET" v e r n i e r i n t h e p o s i t i o n
r e q u i r e d t o reduce t h e n u l l e r r o r t o z e r o , b u t below any l e v e l which induces
oscillations.
After a c h i e v i n g a s t a b l e o p e r a t i n g p o i n t , reduce t h e "MAX. HEATER-AMP''
(Key No. 8) t o a lower s e t t i n g . A s lower s e t t i n g s are d i a l e d i n t h e p e r c e n t (%)
o f maximum, h e a t e r c u r r e n t b e i n g used should i n c r e a s e . The optimum area f o r
c o n t r o l can b e o b t a i n e d by keeping t h e meter p o i n t e r between 0.2 and 0.7 on
t h e meter face.
16
Abruptly i n c r e a s e t h e s e t p o i n t v e r n i e r c o n t r o l by t e n u n i t s , t h e s e n s o r
v o l t a g e now r e p r e s e n t s a t e m p e r a t u r e warmer t h a n t h a t r e p r e s e n t e d by t h e s e t
p o i n t v o l t a g e . The NULL meter should d e f l e c t t o t h e r i g h t and t h e HEATER
CURRENT should go t o z e r o immediately. A s t h e sample h o l d e r c o o l s , t h e
NULL METER p o i n t e r should r e t u r n towards z e r o .
A s t h e NULL METER p o i n t e r approaches z e r o , t h e HEATER CURRENT w i l l
i n c r e a s e from zero t o t h e new s t e a d y s t a t e v a l u e r e q u i r e d t o m a i n t a i n t h e
sample a t t h e lower t e m p e r a t u r e r e q u e s t e d . The NULL METER should r e a d z e r o
as t h e HEATER CURRENT s t a b i l i z e s a t i t s new v a l u e .
Now a b r u p t l y d e c r e a s e t h e set p o i n t v e r n i e r c o n t r o l by t e n u n i t s , t h e
s e n s o r v o l t a g e now r e p r e s e n t s a temperature c o l d e r t h a n t h a t r e p r e s e n t e d by
t h e set p o i n t v o l t a g e . The NULL meter should d e f l e c t t o t h e l e f t and t h e
HEATER CURRENT meter s h o u l d d e f l e c t toward f u l l scale. A s t h e sample h o l d e r
h e a t s , t h e NULL meter p o i n t e r w i l l t e n d t o z e r o and t h e HEATER CURRENT meter
r e a d i n g w i l l d e c r e a s e toward i t s new s t e a d y state value. A s t h e NULL meter
c e n t e r s , t h e HEATER CURRENT s h o u l d s t a b i l i z e at t h e new c o n s t a n t v a l u e
r e q u i r e d t o maintain t h e d e s i r e d t e m p e r a t u r e .
A s k e t c h of t h e t e m p e r a t u r e v e r s u s time p a t t e r n d e s c r i b e d above i s given
i n Figure 3 . 4 . Observe t h a t t h e r e i s no t e m p e r a t u r e overshoot o r o s c i l l a t i o n
when t h e "GAIN" and ''AUTO RESET" c o n t r o l s a r e p r o p e r l y a d j u s t e d .
(This
s t a t e m e n t presupposes t h a t t h e sample h o l d e r , h e a t e r , and s e n s o r may be
a c c u r a t e l y modeled as a simple R-C type time c o n s t a n t thermal c i r c u i t . )
I f o s c i l l a t i o n o r overshoot are observed when changing t h e set p o i n t
v o l t a g e i n small increments, reduce t h e G A I N and i n c r e a s e t h e AUTO RESET time
c o n s t a n t ( r o t a t e CCW) s e t t i n g s u n t i l o s c i l l a t i o n s are no l o n g e r observed
and/or a d j u s t t h e "MAX. HEATER-AMP" (Key No. 8 ) t o a lower s e t t i n g .
3.6
Manual Reset Heating Mode
By p l a c i n g t h e mode s e l e c t o r s w i t c h (Key No. 6 ) i n e i t h e r p o s i t i o n
B , a manually s e t t a b l e c o n s t a n t c u r r e n t may be s u p p l i e d t o
t h e h e a t e r element. The magnitude o f t h e c u r r e n t i s determined by t h e
s e t t i n g o f t h e MAN. RESET p o t e n t i o m e t e r (Key No. 7 ) and t h e MAX. HEATER-AMP.
s w i t c h (Key No. 8 ) . The c u r r e n t s u p p l i e d t o t h e h e a t e r i s i n d i c a t e d on t h e
HEATER CURRENT meter. The f u l l scale r e a d i n g of t h e meter corresponds t o
t h e MAX. HEATER-AMP s w i t c h s e t t i n g .
MAN. A o r MAN.
3.7
Temperature Readout Mode (Sensor B)
In some a p p l i c a t i o n s , t h e temperature i s c o n t r o l l e d ( o r r e g u l a t e d ) a t one
p h y s i c a l l o c a t i o n w h i l e it i s d e s i r e d t o measure t h e t e m p e r a t u r e a t a second
l o c a t i o n . T h i s r e q u i r e s two s e n s o r s , "Sensor A" l o c a t e d a t t h e t e m p e r a t u r e
c o n t r o l p o i n t and "Sensor B" a t t h e second p o i n t where o n l y t h e temperature
is t o be measured. Sensor B must be c a l i b r a t e d .
17
Assume t h a t t h e t e m p e r a t u r e a t Sensor A h a s been s t a b i l i z e d by o p e r a t i n g
t h e c o n t r o l l e r i n t h e c o n s t a n t t e m p e r a t u r e c o n t r o l mode as d e s c r i b e d i n
S e c t i o n 3.5.
By o b s e r v i n g t h e s t e a d y HEATER CURRENT r e a d i n g , one may s w i t c h
t o t h e MAN. A mode as d e s c r i b e d i n S e c t i o n 3.6 and e s t a b l i s h t h i s same c u r r e n t
by a d j u s t i n g t h e MAN RESET p o t e n t i o m e t e r . By a l t e r n a t i n g between t h e AUTO A
and MAN. A modes, t h e MAN RESET p o t e n t i o m e t e r may b e trimmed s u f f i c i e n t l y
a c c u r a t e l y t o h o l d t h e t e m p e r a t u r e s t e a d y o v e r a b r i e f p e r i o d i n t h e MAN. A
p o s i t i o n . Then s w i t c h t o t h e MAN. B p o s i t i o n and q u i c k l y a d j u s t t h e SET POINT
VOLT s w i t c h and p o t e n t i o m e t e r t o z e r o t h e NULL meter. T h i s r e a d i n g i s used
t o determine t h e t e m p e r a t u r e o f Sensor B. After t a k i n g t h e S e n s o r B v o l t a g e
r e a d i n g , reset t h e SET POINT VOLT s w i t c h and p o t e n t i o m e t e r t o t h e d e s i r e d
t e m p e r a t u r e c o n t r o l p o i n t and t h e n r e t u r n t o AUTO A c o n t r o l mode.
I f t h e r e i s a p p r e c i a b l e n u l l e r r o r upon r e t u r n i n g t o t h e AUTO A mode
o f c o n t r o l , t h e adjustment o f t h e MAN RESET c o n t r o l should b e r e f i n e d and
t h e measurement of t h e Sensor B v o l t a g e r e p e a t e d .
S i n c e t h e system i s o p e r a t i n g "open loop" o r i s "coasting" i n both t h e
MAN. A and MAN. B mode o f c o n t r o l p o s i t i o n s , no adjustments o r changes should
be made i n t h e c r y o s t a t system which would i n t r o d u c e t r a n s i e n t s d u r i n g t h i s
p e r i o d of time
.
3.8
Remote Temperature Programming
Remote t e m p e r a t u r e c o n t r o l can be achieved by r e p l a c i n g t h e i n t e r n a l
Kelvin-Varley v o l t a g e d i v i d e r w i t h an e x t e r n a l r e s i s t i v e d i v i d e r connected t o
J 3 and s w i t c h i n g t h e "TEMPERATURE SET POINT'' t o t h e "REMOTE" p o s i t i o n . To
i n s u r e maximum accuracy, t h e t o t a l r e s i s t a n c e between p i n s E-D of J 3 should be
e q u a l t o 615 ohms. The remote set p o i n t connection diagram is shown i n
Figure 3.5.
Equivalent S e t P o i n t Network
Shield
Figure 3.5-Remote Temperature Programming
18
A number of e x t e r n a l temperature programming networks are shown i n Figure 3 . 6 .
Figure 3.6-Programming Networks
The f o l l o w i n g i s a suggested procedure f o r d e s i g n i n g e x t e r n a l temperature
set point control c i r c u i t r y :
1.
Determine t h e range o f d e s i r e d temperature c o n t r o l v o l t a g e .
2.
Choose t h e most s u i t a b l e c o n t r o l c i r c u i t f o r your a p p l i c a t i o n :
-
100%
a,)
Temperature c o n t r o l range
b.)
Limited temperature c o n t r o l range
c.)
Fixed temperature set p o i n t s s e l e c t e d i n s t e p s .
d.)
Most f l e x i b l e arrangement allowing f o r s e l e c t e d
s t e p s and continuously v a r i a b l e temperature s e t
points.
19
Additional v a r i a t i o n s o f t h e above may be t a i l o r e d t o f i t t h e intended
application.
3.
To i n s u r e t h a t t h e t o t a l r e s i s t a n c e between p i n s E & D o f t h e
e x t e r n a l programming v o l t a g e d i v i d e r be o f t h e c o r r e c t value t o
develop a drop o f 3 v o l t s , it is suggested t h a t t h e d i v i d e r
c a l c u l a t i o n be based on more t h a n 210 ohms p e r 1 v o l t and a
s h u n t i n g r e s i s t o r (RT i n F i g . 3.6) used f o r p r e c i s i o n t r i m m i n g
t o 3 v o l t s between p i n s E-D.
The 3.0 v o l t s between p i n s E-D can be measured w i t h a p r e c i s i o n
f l o a t i n g v o l t m e t e r , with t h e s e n s o r c i r c u i t open, i.e. s e n s o r
p l u g s d i s c o n n e c t e d , o r c a l i b r a t e d with t h e DTC-500 i n t e r n a l
set p o i n t v o l t s switch and 10 t u r n d i a l a s f o l l o w s :
a.)
Connect a p r e c i s i o n known r e s i s t o r R (any v a l u e between
50K-250K) t o t h e p i n s AE and BD o f t h e s e n s o r A i n p u t
p l u g J1 (amphenol t y p e 126-217 o r e q u i v a l e n t ) i n p l a c e
o f t h e s e n s o r as shown i n F i g . 3.7, and t u r n t h e s e n s o r
selector s w i t c h on t h e f r o n t panel t o Manual A p o s i t i o n .
Figure 3.7-Programming Voltage
The v o l t a g e drop a c r o s s r e s i s t o r R i s equal t o 10 x 10-6 (amperes)
X R (ohms) v o l t s , t h u s a 100 K ohm r e s i s t a n c e would r e s u l t i n a
1 v o l t drop. With t h e "TEMPERATURE SET POINT" switch on t h e rear
o f t h e i n s t r u m e n t , i n "INTERNAL" p o s i t i o n , t h e n u l l meter w i l l i n d i c a t e
z e r o e r r o r when t h e i n t e r n a l temperature set p o i n t switch on t h e f r o n t
p a n e l is a t 1.000 v o l t s . I n c r e a s e t h e g a i n t o maximum and a d j u s t t h e
10 t u r n d i a l o f t h e i n t e r n a l set p o i n t c o n t r o l i f n e c e s s a r y f o r t h e
n u l l meter t o i n d i c a t e zero. Move t h e r e f e r e n c e s e t p o i n t switch on
t h e rear p a n e l t o e x t e r n a l p o s i t i o n and a d j u s t t r i m r e s i s t o r RT on t h e
e x t e r n a l set p o i n t programming instrument so t h a t t h e n u l l meter reads
zero.
The e x t e r n a l programming network i s now matched t o t h e i n t e r n a l r e f e r e n c e
s o u r c e . Although one p o i n t c a l i b r a t i o n as d e s c r i b e d above i s s u f f i c i e n t ,
it may be d e s i r a b l e t o check s e v e r a l p o i n t s . I n t h a t c a s e , a p r e c i s i o n
r h e o s t a t may be used f o r R a t t h e s e n s o r i n p u t connector, however,
t h e l e a d s as well as t h e d i v i d e r r e s i s t o r should be s h i e l d e d .
20
and t h e s h i e l d s connected t o p i n H of t h e s e n s o r A i n p u t c o n n e c t o r
( J 1 ) . S i m i l a r l y , t h e l e a d s and box housing t h e e x t e r n a l l y programmable
t e m p e r a t u r e r e s i s t a n c e network should be s h i e l d e d through p i n H
of e x t e r n a l s e t p o i n t p l u g (J3).
3.9
Grounding
The c h a s s i s i s grounded by t h e 3 l e a d power c a b l e t o t h e e l e c t r i c a l
supply common ground. The common l e a d o f t h e c o n t r o l l e r c i r c u i t r y ("LO"
t e r m i n a l of t h e h e a t e r o u t p u t - Key 21, F i g . 3.2) i s e x t e r n a l l y connected
t o t h e c h a s s i s ground t e r m i n a l . Although t h e grounding o f t h e c o n t r o l l e r
common i s normal o p e r a t i o n p r a c t i c e , t h e common "Lo" t e r m i n a l may be
d i s c o n n e c t e d from c h a s s i s ground i f doing s o h e l p s t o e l i m i n a t e a c c i d e n t a l
ground loops w i t h i n t h e system.
21
SECTION I V
Theory o f Operation
4.1
Introduction
This s e c t i o n c o n t a i n s t h e t h e o r y o f o p e r a t i o n o f t h e DTC-500 C o n t r o l l e r
and a f u n c t i o n a l c h a r a c t e r i z a t i o n o f t h e c o n t r o l l e r i n Laplace t r a n s f o r m
n o t a t i o n t o a i d t h e thermal system d e s i g n e r i n system s t a b i l i t y a n a l y s i s .
4.2
General D e s c r i p t i o n
Refer t o F i g u r e 3 . 3 and F i g u r e 5 . 2 as an a i d i n t h e f o l l o w i n g d i s c u s s i o n .
With r e f e r e n c e t o Figure 3 . 3 , a p r e c i s i o n c o n s t a n t c u r r e n t s o u r c e causes 10
microamperes o f DC c u r r e n t t o flow through t h e s e n s o r d i o d e . The s e t p o i n t
v o l t a g e s o u r c e ( o r bucking v o l t a g e ) i s s u b t r a c t e d from t h e diode v o l t a g e and
t h e d i f f e r e n c e (or e r r o r ) s i g n a l i s amplified i n a v a r i a b l e gain a m p l i f i e r s t a g e
( o p e r a t i o n a l a m p l i f i e r A2 i n Fig. 5 . 1 ) . The a m p l i f i e d e r r o r i s d i s p l a y e d on
t h e NULL meter and a l s o a p p l i e d t o (1) a g a i n of 20 a m p l i f i e r , (2) an i n t e g r a t o r
c i r c u i t and ( 3 ) a bound o r clamping c i r c u i t . The bounding c i r c u i t d i s a b l e s
t h e i n t e g r a t o r f o r l a r g e e r r o r s . The o u t p u t of t h e i n t e g r a t o r i s a m p l i f i e d by
a v a r i a b l e g a i n a m p l i f i e r whose g a i n i s s e t by t h e AUTO RESET p o t e n t i o m e t e r .
The g a i n range i s from 1 t o 100. The i n t e g r a t o r , bounding c i r c u i t , p o s t
i n t e g r a t o r v a r i a b l e g a i n a m p l i f i e r and c o n s t a n t g a i n o f 20 a m p l i f i e r are
a s s o c i a t e d w i t h o p e r a t i o n a l a m p l i f i e r A3, t r a n s i s t o r Q1 and f i e l d e f f e c t
t r a n s i s t o r 42 i n Figure 5.1.
The processed e r r o r s i g n a l d r i v e s t h e o u t p u t power
a m p l i f i e r c i r c u i t whose v o l t a g e g a i n i s 4 . O p e r a t i o n a l a m p l i f i e r A4 and t r a n s i s t o r s
43 and 44 i n Fig. 5.1 comprise t h e power a m p l i f i e r . The o u t p u t o f t h e power
a m p l i f i e r is metered by t h e HEATER CURRENT i n d i c a t o r and passed t o t h e h e a t e r
element. Closed looped c o n t r o l a c t i o n i s achieved through t h e thermal p a t h
between t h e h e a t e r element and t h e temperature s e n s i n g diode.
To i l l u s t r a t e t h e a u t o m a t i c t e m p e r a t u r e c o n t r o l a c t i o n , suppose t h e s e n s i n g
d i o d e i s c o l d e r t h a n t h e programmed t e m p e r a t u r e s e t t i n g . The d i o d e v o l t a g e w i l l be
g r e a t e r t h a n t h e s e t p o i n t v o l t a g e which r e s u l t s i n an e r r o r v o l t a g e . The
a m p l i f i e d e r r o r s i g n a l causes a c u r r e n t t o flow i n t h e h e a t i n g element which r a i s e s
t h e diode t e m p e r a t u r e and r e d u c e s i t s v o l t a g e . As t h e diode t e m p e r a t u r e approaches
t h e s e t p o i n t t e m p e r a t u r e , t h e e r r o r s i g n a l i s reduced and less power i s s u p p l i e d
t o t h e h e a t e r element. A t some small t e m p e r a t u r e e r r o r ( o r o f f s e t ) t h e power
s u p p l i e d t o t h e h e a t e r element i s j u s t s u f f i c i e n t t o h e a t t h e sample h o l d e r and
d i o d e t o m a i n t a i n a s t e a d y b u t s l i g h t l y lower temperature. The AUTOMATIC RESET
f e a t u r e o f t h e c o n t r o l l e r is used t o reduce t h i s e r r o r t o z e r o . The automatic
r e s e t c i r c u i t i n t e g r a t e s t h e e r r o r and t h i s accumulated s i g n a l d r i v e s t h e o u t p u t
power a m p l i f i e r . The i n t e g r a t o r s i g n a l c o n t i n u e s t o grow as long as an e r r o r
e x i s t s . The h e a t e r c u r r e n t c o n t i n u e s t o i n c r e a s e i n r e s p o n s e t o t h e i n t e g r a t o r
s i g n a l . E v e n t u a l l y , t h e e r r o r is d r i v e n t o z e r o and t h e i n t e g r a t o r s i g n a l
assumes a c o n s t a n t v a l u e . T h i s s i g n a l i s p r e c i s e l y t h e v a l u e o f h e a t e r c u r r e n t
r e q u i r e d t o m a i n t a i n t h e e r r o r a t zero. The i n t e g r a t o r c a p a c i t o r s t o r e s o r
"remembers" t h i s s i g n a l as t h e a p p r o p r i a t e h e a t e r c u r r e n t l e v e l t o maintain
t e m p e r a t u r e c o i n c i d e n c e between t h e diode and t h e s e t p o i n t t e m p e r a t u r e . I n
c o n t r o l t h e o r y * terminology, t h e AUTO RESET c i r c u i t raises t h e system t y p e number
from z e r o t o one.
*"Feedback Control System Analysis and S y n t h e s i s " by John J . D ' A Z Z O and
C o n s t a n t i n e H. Houpis, M c G r a w - H i l l Book Co., New York, 1966, Pg. 397.
22
FIGURE 4.1
SIMPLIFIED EQUIVALENT CIRCUIT OF
AUTOMATIC RESET AMPLIFER
23
4.3
Detailed Description
Regulated Power S u p p l i e s
There are f o u r r e g u l a t e d supply v o l t a g e s i n t h e instrument.
are d e s i g n a t e d as P/S-1 through P/S-4 i n Figure 5.1.
(a)
They
Reference Current
R e f e r r i n g t o Fig. 5.1, power supply P/S-1 and U 1 p r o v i d e s ±15 Volts DC
t o t h e o p e r a t i o n a l a m p l i f i e r c o n s t a n t c u r r e n t s o u r c e as well as i t s c u r r e n t
r e f e r e n c e f o r 10 microamperes b i a s c u r r e n t .
(b)
Diode Constant Current Supply
Power supply P/S-1 and o p e r a t i o n a l amplifier A 1 C o n s t i t u t e t h e main
components i n t h e diode c o n s t a n t c u r r e n t supply. Due t o t h e high i n p u t
impedance o f t h e o p e r a t i o n a l a m p l i f i e r A l , t h e diode c u r r e n t i s f o r c e d t o
flow through r e s i s t o r R5 developing 4.99V a t 10 microamperes. The v o l t a g e
a c r o s s R5 i s t h e r e f o r e equal t o t h e v o l t a g e a t t h e i n v e r t i n g i n p u t (-)
t e r m i n a l o f A 1 w i t h a v o l t a g e o f 4.99V a p p l i e d t o t h e n o n - i n v e r t i n g (+)
i n p u t o f A 1 by t h e r e f e r e n c e c i r c u i t o f R 1 , R2, R 3 , R4 and CR5. The c u r r e n t
through R5 (4.99 K) w i l l maintain t h e r e g u l a t e d c u r r e n t through s e n s o r t o
10 microamperes.
The e n t i r e c o n s t a n t c u r r e n t supply system was designed t o be f u l l y f l o a t i n g
s o t h a t t h e cathode o f t h e s e n s o r diode might b e r e t u r n e d t o common.
(c)
S e t P o i n t Voltage Supply and Divider
F l o a t i n g power supply P/S-2 p r e r e g u l a t e s t h e v o l t a g e used t o supply
r e f e r e n c e diode CR-12. The doubly r e g u l a t e d v o l t a g e appearing between t i e p o i n t
(TP) 5 and t h e cathode o f C R - 1 2 i s a p p l i e d t o a 3 s t a g e Kelvin-Varley v o l t a g e
d i v i d e r c o n s i s t i n g o f R101-Rl19, R 1 2 , R12A, R16, and R17. The set p o i n t v o l t a g e
p r o p e r c o n s i s t s of t h e p o t e n t i a l developed between t i e p o i n t 5 and t h e wiper o f
p o t e n t i o m e t e r R119.
The f l o a t i n g set p o i n t v o l t a g e power supply and Kelvin-Varley v o l t a g e
d i v i d e r c o n s t i t u t e a p o t e n t i o m e t e r loop. When t h e set p o i n t v o l t a g e p r o p e r e q u a l s
t h e s e n s o r diode v o l t a g e , no e r r o r s i g n a l appears a t t h e i n p u t t e r m i n a l s o f
p r e a m p l i f i e r A2.
(d)
Amplifier Supply Voltages
R e f e r r i n g t o Fig. 5.1, power supply P/S-3 p r o v i d e s ±15 Volts DC t o t h e
c i r c u i t r y i n c l u d i n g o p e r a t i o n a l amplifiers A 2 , A3, and A4, e t c .
(e)
V a r i a b l e Gain Amplifier
The v a r i a b l e gain a m p l i f i e r shown i n Fig. 3.3, w i t h a gain range o f 5 t o
The i n p u t
r e s i s t o r i s R8 and t h e feedback element c o n s i s t s of R10, R 1 1 , R13, and R15 o r
R10, R 1 1 , R14, and R15.
509, i s r e a l i z e d by c h o p p e r - s t a b i l i z e d o p e r a t i o n a l a m p l i f i e r A 2 .
24
Diodes CR-13, 1 4 , 15, 16 and R9 comprise limiter c i r c u i t r y . Large
s i g n a l s cause forward b i a s e d diodes t o conduct which i n t u r n reduces t h e
e f f e c t i v e feedback resistance and a m p l i f i e r g a i n , and p r e v e n t s t h e a m p l i f i e r
from s a t u r a t i n g .
The o u t p u t of a m p l i f i e r A 2 d r i v e s t h e n u l l meter and subsequent s t a g e A3.
For small e r r o r s , t h e meter r e a d i n g i s p r o p o r t i o n a l t o t h e e r r o r . A s t h e e r r o r
amplitude increases, e i t h e r d i o d e CR-17 o r CR-18 conducts c a u s i n g t h e meter
r e a d i n g t o b e l o g a r i t h m i c . Cross-over from linear t o n o n - l i n e a r d e f l e c t i o n occurs
a t approximately 70% o f f u l l scale from c e n t e r .
(f)
Automatic-Reset C i r c u i t , Bounding C i r c u i t
The bound c i r c u i t , v a r i a b l e gain i n t e g r a t o r , and t h e c o n s t a n t gain
a m p l i f i e r shown i n Fig. 3.3 are r e a l i z e d by o p e r a t i o n a l a m p l i f i e r A3, b i p o l a r
t r a n s i s t o r Q 1 and f i e l d e f f e c t t r a n s i s t o r Q2 i n Fig. 5.1. A s i m p l i f i e d
e q u i v a l e n t c i r c u i t o f t h e s t a g e i s given i n Fig. 4.1.
Application of t h e p r i n c i p l e t h a t t h e summing j u n c t i o n c u r r e n t s must add t o
zero y i e l d s t h e o v e r a l l t r a n s f e r f u n c t i o n of t h e s t a g e . The c o n s t a n t gain
a m p l i f i e r i n Fig. 3.3 is r e p r e s e n t e d by t h e term R32/R23 w h i l e t h e v a r i a b l e
g a i n a m p l i f i e r following t h e i d e a l i n t e g r a t o r i s r e p r e s e n t e d by t h e term
(1 + R32/Re)/R23C16 i n t h e e q u a t i o n i n Fig. 4.1.
The bounding c i r c u i t d i s a b l e s t h e i n t e g r a t i n g f u n c t i o n f o r l a r g e e r r o r s
when r a p i d c o r r e c t i v e a c t i o n is d e s i r e d . The memory a c t i o n o f i n t e g r a t i n g
c a p a c i t o r C16 causes t h e c o n t r o l l e r t o be s l u g g i s h i n such t r a n s i e n t o p e r a t i o n s .
The method o f d i s a b l i n g t h e c a p a c i t o r depends upon t h e s i g n o f t h e e r r o r and t h e
p o l a r i t y o f t h e v o l t a g e a c r o s s C16. I f t h e v o l t a g e a c r o s s c a p a c i t o r C5 i s of
such a p o l a r i t y a s t o make TP19 p o s i t i v e with r e s p e c t t o TP17, diode CR-25
conducts reducing t h e e f f e c t i v e gain o f t h e stage and d i s c h a r g i n g t h e c a p a c i t o r .
The second mode o f bounding o c c u r s i f t h e error s i g n a l a t t h e b a s e of Q 1
becomes e x c e s s i v e l y n e g a t i v e . Q 1 i s normally b i a s e d by CR-19 s o t h a t f i e l d e f f e c t
t r a n s i s t o r Q2 is c u t - o f f (approximately -9V) a t t h e gate. A s t h e base o f Q 1
becomes more n e g a t i v e , Q 1 conducts c u r r e n t , i n c r e a s i n g t h e c o l l e c t o r v o l t a g e
toward zero. The reduced b i a s on FET Q2 causes its s o u r c e - d r a i n impedance t o
a c t a s a shunt r e s i s t o r a c r o s s c a p a c i t o r C16. T h i s s h u n t i n g e f f e c t d i s c h a r g e s
t h e C a p a c i t o r and c o n v e r t s t h e i d e a l i n t e g r a t o r a c t i o n t o a type z e r o a c t i o n .
The s w i t c h S3 i s c l o s e d when t h e AUTO RESET c o n t r o l is i n t h e o f f p o s i t i o n .
(g)
Output Power Amplifier
The processed e r r o r s i g n a l appearing a t TP18 i s g r e a t l y a m p l i f i e d i n power
by op-amp A4, Q3, and Q4 b e f o r e b e i n g a p p l i e d t o t h e h e a t e r element. T r a n s i s t o r s
Q3 and Q4 c o n s t i t u t e a Darlington series p a s s element i n a c u r r e n t a m p l i f i e r
c i r c u i t . They are i n s i d e t h e feedback loop a s s o c i a t e d with op-amp A4, R46 b e i n g
t h e feedback r e s i s t o r . The i n p u t r e s i s t o r f o r t h e op-amp i s R37 so t h a t t h e
v o l t a g e gain o f t h e power a m p l i f i e r c i r c u i t i s R46/R37 or approximately 3.5.
A t r a t e d o u t p u t c u r r e n t o f one ampere, t h e v o l t a g e appearing at TP20 i s -10.5
v o l t s . Use of a h e a t e r r e s i s t a n c e i n excess of t e n ohms w i l l reduce t h e a v a i l a b l e
h e a t e r c u r r e n t below t h e r a t e d maximum value of 1 ampere. (See a p p l i c a t i o n n o t e s
i n Section VI.)
25
Winding 5-6-7 on t r a n s f o r m e r P/S-4, diodes CR-28 and CR-29 and c a p a c i t o r
C18 c o n s t i t u t e s t h e power s u p p l y f o r t h e series p a s s elements Q3 and Q4.
(h)
Manual Heater Current Control
When t h e mode s e l e c t o r s w i t c h i s set t o e i t h e r MAN A o r MAN B p o s i t i o n ,
s w i t c h s e c t i o n S1-F connects t h e i n p u t of t h e power a m p l i f i e r s t a g e t o t h e
wiper o f p o t e n t i o m e t e r R38. Varying t h e wiper p o s i t i o n from z e r o t o i t s
maximum w i l l vary t h e v o l t a g e a t TP20 from z e r o t o approximately -10.5 v o l t s .
The h e a t e r element c u r r e n t i s t h u s v a r i e d p r o p o r t i o n a t e l y t o t h e s e t t i n g o f
R38 and t h e maximum h e a t e r c u r r e n t s w i t c h (S4) p o s i t i o n .
(i)
Heater Current Metering and L i m i t i n g
The h e a t e r element c u r r e n t i s measured by t h e h e a t e r c u r r e n t ammeter,
shunted by r e s i s t o r R201 through R205 as a p p r o p r i a t e f o r t h e c u r r e n t range
s e l e c t e d . The f u l l scale o u t p u t c u r r e n t i s determined by t h e series
combination o f t h e h e a t e r element r e s i s t a n c e and one o f t h e group o f r e s i s t o r s
R206 through R209. T h i s s e r i e s combination is connected a c r o s s t h e nominal
-10.5 v o l t o u t p u t o f t h e power a m p l i f i e r . Approximately .5 v o l t s appears
a c r o s s t h e Heater Current Meter (M1) and R200 and i t s a p p r o p r i a t e s h u n t
resist o r .
Under no circumstances s h a l l t h e r a t i n g of f u s e FU2 be i n c r e a s e d above
one ampere i n an a t t e m p t t o a c h i e v e a power d i s s i p a t i o n o f t e n watts i n a
h e a t e r element whose r e s i s t a n c e i s less t h a n t e n ohms. Such a s u b s t i t u t i o n
i n v a l i d a t e s t h e i n s t r u m e n t w a r r a n t y and i s l i k e l y t o damage t h e o u t p u t power
amplifier circuit.
26
SECTION V
Maintenance and Troubleshooting
5.1
Introduction
This s e c t i o n c o n t a i n s i n s t r u c t i o n s f o r m a i n t a i n i n g and c a l i b r a t i n g
t h e c o n t r o l l e r , nominal v o l t a g e v a l u e s and g a i n s , c i r c u i t schematic diagram,
p r i n t e d c i r c u i t board component diagram and p a r t s l i s t .
5.2
Test Equipment and A c c e s s o r i e s
An RCA S e n i o r Voltohmist vacuum t u b e v o l t m e t e r o r an e q u i v a l e n t h i g h i n p u t
impedance d i g i t a l v o l t m e t e r ; a t e n ohm, t e n watt r e s i s t o r t o s i m u l a t e t h e h e a t e r
element; and a p r e c i s i o n r e s i s t o r connected t o s i m u l a t e t h e d i o d e i n a connector
assembly wired a c c o r d i n g t o Fig. 2.1 ( c ) a r e normally s u f f i c i e n t f o r t e s t i n g
and c a l i b r a t i n g t h e DTC-500 C o n t r o l l e r .
5.3
General Remarks
Upon i n i t i a l i n s t a l l a t i o n , t h e s i n g l e most p r o b a b l e cause o f system malf u n c t i o n i s an improperly connected t e m p e r a t u r e s e n s i n g diode. I f i t i s
impossible t o z e r o t h e n u l l meter a t any s e t t i n g of t h e s e t p o i n t v o l t a g e
c o n t r o l s , c a r e f u l l y examine t h e c a b l e / d i o d e assembly t o i n s u r e t h a t t h e d i o d e
p o l a r i t y i s c o r r e c t , t h a t t h e s e n s o r i s plugged i n t o t h e "SENSOR A" r e c e p t a c l e
and t h a t t h e "TEMPERATURE SET POINT/INTERNAL/REMOTE" s l i d e s w i t c h a t t h e r e a r
o f t h e c a s e is i n t h e INTERNAL p o s i t i o n .
Because of t h e h i g h l y r e l i a b l e s o l i d s t a t e d e s i g n o f t h e c o n t r o l l e r , it
i s most u n l i k e l y t h a t t h e c o n t r o l l e r w i l l be a s o u r c e o f d i f f i c u l t y . For t h i s
r e a s o n , it i s a d v i s a b l e t o examine o t h e r p o r t i o n s of t h e cryogenic system
b e f o r e t e s t i n g t h e c o n t r o l l e r p r o p e r . Some s u g g e s t e d checks a r e :
(1)
(2)
(3)
(4)
(5)
Open o r s h o r t e d s e n s o r and h e a t e r l e a d s , p a r t i c u l a r l y i n t h e v i c i n i t y
o f t h e sample h o l d e r i f i t i s s u b j e c t t o f r e q u e n t dis-assembly.
Leakage p a t h s between h e a t e r and s e n s o r l e a d s g i v i n g r i s e t o
e l e c t r i c a l feedback i n a d d i t i o n t o thermal feedback.
Premature l o s s o f c r y o g e n i c f l u i d due t o thermal s h o r t s i n dewar,
i c e b l o c k s i n l i n e s , sample h o l d e r immersed i n cryogen, sample
h o l d e r i n vapor whose t e m p e r a t u r e is above t h e c o n t r o l l e r s e t p o i n t
temperature, e t c .
Excessive thermal p a t h phase l a g s w i l l cause t h e c o n t r o l loop t o
be u n s t a b l e a t h i g h g a i n s e t t i n g s . P h y s i c a l s e p a r a t i o n between
t h e diode and h e a t e r , p a r t i c u l a r l y by p a t h s o f small thermal
c r o s s - s e c t i o n should b e avoided.
Examine h e a t e r element f u s e FU2.
If i t i s i n d i c a t e d t h a t t h e c o n t r o l l e r i s malfunctioning a f t e r performing
t h e t e s t s t o be d e s c r i b e d below, i t i s recommended t h a t t h e i n s t r u m e n t be
r e t u r n e d t o t h e f a c t o r y f o r r e p a i r . The components used i n t h e i n s t r u m e n t a r e
27.
c o s t l y and may b e permanently damaged i f s u b j e c t e d t o i n a p p r o p r i a t e t e s t
v o l t a g e s o r e x c e s s i v e s o l d e r i n g i r o n h e a t . Although premium materials and
t e c h n i q u e s have been used t o f a b r i c a t e t h e instrument c i r c u i t board, t h e r e
i s always t h e r i s k o f l i f t i n g a connection pad o r c r a c k i n g t h e board when
u n s o l d e r i n g a component.
5.4
S e r v i c i n g P r i n t e d C i r c u i t Boards
I t i s suggested t h a t components be unsoldered f o r t r o u b l e s h o o t i n g only
as a l a s t r e s o r t s i n c e ample i n f o r m a t i o n i s a v a i l a b l e a t t h e numbered t e r m i n a l
p i n s . Attempt t o i n f e r component c u r r e n t s by v o l t a g e t e s t s r a t h e r t h a n removing
a l e a d and s e r i e s i n g i t w i t h an ammeter. A l l v o l t a g e s a r e a v a i l a b l e f o r
measurement from t h e t o p s i d e o f t h e p r i n t e d c i r c u i t board. T h e r e f o r e , t h e
board need o n l y be removed when it i s n e c e s s a r y t o r e p l a c e a component. To
remove t h e p r i n t e d c i r c u i t board, unscrew t h e b o l t s from t h e bottom o f t h e case
which a t t a c h t h e board t o t h e s t a n d - o f f s t u d s .
Swing t h e rear of t h e board up, u s i n g t h e f r o n t edge as a p i v o t . Be s u r e
t o c l e a r t h e l i n e cord r e t a i n e r and f u s e h o l d e r s . Be s u r e t o s u p p o r t t h e board
i n t h e r a i s e d p o s i t i o n . If t h e board i s s t r e s s e d , i t may break o r develop
h a i r l i n e cracks i n t h e printed wiring.
Use a low h e a t (25 t o 50 w a t t s ) s m a l l - t i p , f r e s h l y t i n n e d s o l d e r i n g i r o n .
Use small d i a m e t e r , r o s i n c o r e s o l d e r . Remove a component l e a d by a p p l y i n g
h e a t t o t h e l e a d , o b s e r v i n g t h e s o l d e r melt and t h e n p u l l i n g t h e l e a d through
t h e board from t h e t o p s i d e . Never apply t e n s i o n t o p r i n t e d w i r i n g from t h e
bottom s i d e .
Thoroughly c l e a n a l l of t h e o l d s o l d e r from t h e mounting h o l e b e f o r e i n s e r t i n g a new component w i t h t h e u s e of a w i c k o r d e s o l d e r i n g s u c t i o n d e v i c e .
Shape t h e new component and i n s e r t i n mounting h o l e . Do n o t u s e h e a t . o r f o r c e
t o i n s e r t t h e new component. I f t h e l e a d s w i l l n o t go through t h e h o l e , f i l e t h e
l e a d o r c l e a n t h e h o l e more thoroughly. Once mounted p r o p e r l y , apply h e a t t o l e a d
and w i r i n g pad s i m u l t a n e o u s l y and r e s o l d e r . Clean excess f l u x from t h e connection
and a d j o i n i n g area w i t h w a r m water and weak d e t e r g e n t i f need be. (Contamination
i n some areas o f t h e board can s e r i o u s l y degrade t h e h i g h i n p u t impedance o f t h e
o p e r a t i o n a l a m p l i f i e r s .)
5.5
O p e r a t i o n a l Checks
Replace t h e s e n s o r d i o d e connector p l u g w i t h a t e s t p l u g made up a c c o r d i n g
t o Fig. 2 . 1 ( c ) . S u b s t i t u t e a p r e c i s i o n r e s i s t o r f o r t h e s e n s o r d i o d e i n t h e
t e s t p l u g . Remove t h e h e a t e r element l e a d s and p l a c e a t e n watt, t e n ohm
r e s i s t o r across t h e heater output terminals.
Ten microamperes flowing through t h e t e s t r e s i s t o r should develop a
p o t e n t i a l o f 1.00 v o l t s a c r o s s a 100 K ohm r e s i s t o r . With t h e gain s e t a t maximum
p o s i t i o n and t h e mode s e l e c t o r s w i t c h i n p o s i t i o n MAN A (assuming t h e t e s t p l u g
i s i n SENSOR A r e c e p t a c l e ) , a t t e m p t t o n u l l t h e e r r o r w i t h a s e t p o i n t v o l t a g e
i n t h e v i c i n i t y o f 1.0 v o l t s . The n u l l meter should swing smoothly as t h e s e t
p o i n t v o l t a g e v e r n i e r i s v a r i e d i n t h e v i c i n i t y of t h e n u l l .
28
While s t i l l i n t h e MAN A p o s i t i o n , s e t t h e MAXIMUM HEATER AMP switch
a t 1 amp. Vary t h e MAN. RESET p o t e n t i o m e t e r from zero towards i t s maximum.
The c u r r e n t meter should i n c r e a s e l i n e a r l y along w i t h t h e advance of t h e
MAN RESET c o n t r o l . With t h e MAN RESET c o n t r o l s e t t o g i v e mid-scale h e a t e r
c u r r e n t meter d e f l e c t i o n , r o t a t e t h e MAX HEATER AMP s w i t c h through a l l o f
i t s p o s i t i o n s . The h e a t e r c u r r e n t meter i n d i c a t i o n should remain approximately
a t mid-scale i n a l l o f t h e p o s i t i o n s .
Zero t h e n u l l meter w i t h t h e set p o i n t v o l t a g e c o n t r o l s . Turn t h e
AUTO RESET and G A I N c o n t r o l s t o mid-scale p o s i t i o n . S e t t h e MAX HEATER
CUR. s w i t c h t o 1 amp. P o s i t i o n t h e mode c o n t r o l s w i t c h t o AUTO A. Abruptly
r o t a t e t h e set p o i n t v o l t a g e v e r n i e r c o u n t e r clockwise s u f f i c i e n t l y t o cause
a -10 u n i t d e f l e c t i o n o f t h e NULL meter t o t h e l e f t . The h e a t e r c u r r e n t meter
d e f l e c t i o n w i l l c o n s i s t of two components. The f i r s t i s a r a p i d s t e p rise
due t o t h e s t e a d y n u l l e r r o r and a second, g r a d u a l l y r i s i n g component due t o
t h e AUTO RESET c i r c u i t i n t e g r a t i n g t h e s t e a d y e r r o r . The h e a t e r c u r r e n t
meter w i l l g r a d u a l l y rise towards f u l l scale d e f l e c t i o n . The r a t e a t which
t h e h e a t e r c u r r e n t rises is determined by t h e AUTO RESET time c o n s t a n t
s e t t i n g . The rate i s a minimum i n t h e counterclockwise p o s i t i o n and a
maximum i n t h e f u l l y clockwise p o s i t i o n .
Abruptly r o t a t e t h e s e t p o i n t v o l t a g e v e r n i e r clockwise t o cause +10
u n i t s d e f l e c t i o n o f t h e NULL meter t o t h e r i g h t . The HEATER CURRENT meter
should g r a d u a l l y d e c r e a s e from f u l l scale d e f l e c t i o n t o zero. The r a t e a t
which t h e c u r r e n t meter goes t o z e r o i s i n p a r t determined by t h e bounding
c i r c u i t . I t s n o n - l i n e a r b e h a v i o r accounts f o r t h e asymetry i n t h e temperature
v e r s u s time c h a r a c t e r i s t i c s as shown i n Fig. 3.4.
If t h e i n s t r u m e n t responds t o t h e t e s t s o u t l i n e d above as i n d i c a t e d ,
e i t h e r t h e t r o u b l e l i e s elsewhere i n t h e system o r t h e malfunction i n t h e
c o n t r o l l e r i s o f a s u b t l e n a t u r e . A s an a i d i n t r o u b l e s h o o t i n g i n t h e
l a t t e r case, t y p i c a l v o l t a g e s and g a i n s under s p e c i f i e d c o n d i t i o n s are given
i n S e c t i o n 5.6.
5.6
Nominal Operating Voltages and Gains
The following v o l t a g e measurements were made w i t h an RCA S e n i o r Voltohmist
meter. A 1%,75 K ohm r e s i s t o r was used t o s i m u l a t e t h e diode and a 10 ohm,
10 watt r e s i s t o r was used i n p l a c e o f a h e a t e r element.
The v o l t a g e a c r o s s t h e i n p u t f i l t e r c a p a c i t o r s C 1 , C 2 , C9, C10 and C 1 1
i n power s u p p l i e s P/S-1 through P/S-3 are nominally 24 v o l t s w i t h t h e o u t p u t
v o l t a g e s appearing a c r o s s c a p a c i t o r s C14, C13, C8, C14, and C15 being
±15 v o l t s , +15 v o l t s , and ±15 v o l t s r e s p e c t i v e l y .
Reference diodes CR-5 and C R - 1 2 are r e v e r s e b i a s e d a t 6 . 4 v o l t s .
The v o l t a g e appearing a c r o s s c a p a c i t o r C18 and P/S-4 v a r i e s between
approximately 14 and 20 v o l t s , depending upon t h e h e a t e r element c u r r e n t . A t
no load t h e v o l t a g e i s 20 v o l t s , d e c r e a s i n g t o 1 4 v o l t s a t 1 ampere output.
29
The emitter o f Q 1 is b i a s e d t o +0.5V t o compensate f o r t h e t u r n on
v o l t a g e of Q1.
The o u t p u t power a m p l i f i e r stage may be checked by p l a c i n g t h e mode
selector s w i t c h i n t h e MAN A p o s i t i o n . The p o t e n t i a l a c r o s s R38 ( t e r m i n a l s
6 t o 7) i s 3.2 v o l t s . The v o l t a g e a t t e r m i n a l 20 should be approximately
3.5 times t h e v o l t a g e s e l e c t e d between t h e s l i d e r of R38 and ground. The
v o l t a g e a t t h e o u t p u t of a m p l i f i e r A4 i s about one v o l t more n e g a t i v e t h a n
t h e v o l t a g e a t t e r m i n a l 20 because o f t h e b a s e emitter drops of 43 and 44.
With t h e AUTO RESET c o n t r o l i n t h e off p o s i t i o n ( i n t h e switch d e t e n t )
and t h e MAX HEATER CUR switch i n t h e 1 amp. p o s i t i o n , t h e t o t a l v o l t a g e gain
of a m p l i f i e r s A 3 and A4 may be i n f e r r e d . The CURRENT METER corresponds t o
a 10 v o l t f u l l s c a l e v o l t m e t e r i f a 10 ohm h e a t e r element i s used. Comparison
of t h e incremental o u t p u t v o l t a g e change t o t h e corresponding incremental
NULL meter e r r o r change w i l l y i e l d t h e g a i n . The nominal cascade g a i n o f
t h e l a s t two s t a g e s i s 60.
Gain checks should be performed by first z e r o i n g t h e NULL meter with t h e
SET POINT VOLTAGE VERNIER. A small v o l t a g e change is made i n t h e v e r n i e r
d i a l s e t t i n g and t h e r e s u l t i n g changes i n t h e NULL meter and CURRENT meters
observed.
5.7
C a l i b r a t i o n o f S e t P o i n t Voltage
The i n s t r u m e n t has been c a r e f u l l y c a l i b r a t e d t o w i t h i n 100 m i c r o v o l t s
p l u s a r e s i d u a l base l i n e r e s i s t a n c e of t h e 10 t u r n p o t e n t i o m e t e r R119.
Should it be d e s i r a b l e t o check or r e c a l i b r a t e t h e set p o i n t r e f e r e n c e
v o l t a g e , t h e s e n s o r should be disconnected and t h e "TEMPERATURE SET POINT"
s w i t c h on t h e back p a n e l be i n t h e "INTERNAL'' p o s i t i o n . The r e f e r e n c e v o l t a g e
may b e measured between p i n E o f J1 and p i n D o f J3 w i t h o u t opening t h e case cover.
Voltage measurements should b e taken w i t h a high p r e c i s i o n p o t e n t i o m e t r i c
instrument. I f r e c a l i b r a t i o n i s i n d i c a t e d , a f t e r allowing a minimum o f
20 minutes warm-up t i m e , a d j u s t trimmer R12 s o t h e v o l t a g e between t e r m i n a l
p i n s 5 and 3 i s 3.0000 ±100 uV.
5.8
C a l i b r a t i o n o f Sensor Current
The s e n s o r c u r r e n t has been f a c t o r y c a l i b r a t e d t o 10 microamperes
±10 nanoamperes. To check t h e s e n s o r c u r r e n t without removing t h e c a s e cover,
a c o n v e n i e n t l y a v a i l a b l e p r e c i s i o n r e s i s t a n c e o f n o t less than .01% t o l e r a n c e
should be connected t o p i n s A-B o f t h e s e n s o r connector s o c k e t ( J 1 o r J 2 ) , and
t h e s e n s o r s e l e c t o r switch on t h e f r o n t p a n e l switched t o t h e a p p r o p r i a t e s e n s o r
i n p u t (A o r B ) . The "TEMPERATURE SET POINT" switch on t h e r e a r p a n e l should be
switched t o "REMOTE", and remote p l u g (20) be disconnected.
A high q u a l i t y p o t e n t i o m e t r i c v o l t m e t e r connected t o t h e p r e c i s i o n r e s i s t o r
should measure a v o l t a g e equal t o 10 microamperes times t h e value o f t h e r e s i s t o r .
T y p i c a l l y , a 100 K ±.01% r e s i s t o r should r e a d 1.0000 w i t h i n 100 m i c r o v o l t s . I f
r e c a l i b r a t i o n is i n d i c a t e d , t h e v o l t a g e a c r o s s t h e p r e c i s i o n r e s i s t o r s can be
r e c a l i b r a t e d a f t e r removing t h e case cover and a d j u s t i n g trimmer R 3 on t h e
c i r c u i t board.
30
5.9
Parts L i s t , Component Location Diagram and Schematic
Table 5 . 1
PARTS LIST
R1
R2
R3
R4
R5
R6
R7
R8
R9
R10
R11
R12
R12A
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22
R23
R24
R25
R26
R27
R28
R29
R30
R31
R32
R33
R34
R35
R36
R37
R38
R39
R40
R41
R42
1%
7.87K
1/8W
10.3K
1/8W
1%
1 K H e l i t r i m 78 PR 1 K
(Current Adjust)
40.1K
1%
499K
1/8W
1%
470
1/4W
5%
100K
1/4W
5%
100K
1/4W
5%
511
1/4w
5%
2K
1/4W
5%
2.2M
1/4W
5%
10 ohm Helitrim 78 PR 10 (Gain C o n t r o l )
10
1/8W
1%
25K POTENTIOMETER (Gain C o n t r o l )
25K
1/4W
5%
300
1/8W
1%
(TRIM-NOMINAL)
698 (NOMINAL) 1/8W
1%
1.47K
1/8W
1%
10
1/4W
5%
10
1/4W
5%
464
1/8W
1%
8.68K
1/8W
1%
332K
1/8W
1%
(TRIM-NOMINAL)
470
1/4W
5%
(TRIM-NOMINAL)
100K
1/4W
5%
18K
1/4W
5%
680K
1/4W
5%
1/4W
5%
2.7M
2.4K
1/4W
5%
1M
1/4W
5%
1 Meg POTENTIOMETER (AUTO RESET)
1K
1/4W
5%
1.2K
1/4W
5%
1.2K
1/4W
5%
15K
1/8W
1%
1K
10 TURN. POT. (MANUAL RESET)
3.92K
1/8W
1%
1/4W
5%
33K
12K
1/4W
5%
1/4W
5%
1.5K
31
R43
R44
R45
R46
R101-104
R105-106
R107-117
R118
R119
R200
R201
R202
R203
R204
R205
R206
R207
R208
R209
(OPTIONAL)
51K
1/4W
12K
1/4W
56K
1/4W
200
1/8W
TRIMMING RESISTORS
1/8W
48.7
TRIMMING RESISTORS
100 ohm
475
1/8W
54.9
1/4W
16.9
1/8W
4.99
1/8W
1.64
1/2w
0.4925
1w
1000
1/4W
1/2w
324
90
2w
23.33
5w
c1
100 MFD, 50 VDC, E l e c t r o l y t i c
100 MFD, 50 V, E l e c t r o l y t i c
10 MFD, 25 V, Tantalum
10 MFD, 25 V, Tantalum
0.25 MFD, 50 V, Mylar
0.68 MFD, 50 V, Mylar
0.16 MFD, 50 V, Mylar
10 MFD, 25 V, Tantalum
100 MFD, 50 VDC, E l e c t r o l y t i c
400 MFD, 50 VDC, E l e c t r o l y t i c
400 MFD, 50 V , E l e c t r o l y t i c
0.0015 MFD, 50 V, Mylar
0.0015 MFD, 50 V, Mylar
2.7 MFD, 25 V, Tantalum
2.7 MFD, 25 V, Tantalum
100 MFD, 1 5 V, Tantalum
0.0056 MFD, 25 V, Ceramic
2500 MFD, 25 V, E l e c t r o l y t i c
0.027 MFD, 50 V, Mylar
c2
c3
c4
c5
C6
c7
C8
c9
c10
c11
c12
C13
C14
C15
C16
C17
C18
c19
5%
5%
.05%
.05%
SET POINT
VOLTAGE D I V I D E R
ASSEMBLY
HEATER CURRENT
RANGE AND
METER SWITCH
ASSEMBLY
1%
1%
1%
32
CR1-4
CR5
CR6-7
CR8-11
CR12
CR13
CR14
CR15
CR16
CR17
CR18
CR19
CR20-23
CR24
CR25
CR26
CR27
CR28
CR29
SILICON RECTIFIER
REFERENCE DIODE
S I L I C O N PROTECTIVE DIODE
RECTIFIER
REFERENCE DIODE
S I L I C O N PROTECTION DIODE
S I L I C O N PROTECTION DIODE
ZENER DIODE, 10 V
ZENER DIODE, 10 V
GERMANIUM PROTECTION DIODE
GERMANIUM PROTECTION DIODE
S I L I C O N DIODE
RECTIFIER
ZENER DIODE, 4 V
S I L I C O N DIODE
S I L I C O N DIODE
S I L I C O N DIODE
SILICON RECTI F I ER
SILICON RECTIFIER
A1
A2
A3
A4
OPERATIONAL
OPERATIONAL
OPERATIONAL
O P E RATIONAL
AMPLIFIER
AMPLIFIER
AMPLIFIER
AMPLIFIER
u1
u2
u3
VOLT. REG.,
VOLT. REG.,
VOLT. REG.,
RC 4195 ON
78 M15 HC
MC 1468 R
Q1
Q3
Q4
2N4249
2N5459
2N4234
2N4901
S1
S2
S3
S4
S5
S6
S7
MODE SELECTOR SWITCH
S E T P O I N T SWITCH ASSEMBLY
PART O F POTENTIOMETER R 5 5
HEATER CURRENT METERING SW. ASSEMBLY
POWER SW., A.H. & H. 8 1 0 2 4 - G B
L I N E VOLTAGE SELECTOR S W I T C H , SWITCHCRAFT 4 6 2 5 6 L F
TEMP. S E T P O I N T INTERNAL, REMOTE SELECTOR SWITCH, SWITCHCRAFT 4 6 2 0 6 L
Q2
IN4004
IN4571A
411
IN4004
IN4571A
411
411
1n358
1n358
1n645
IN4004
1n814
411
1n645
IN1612
IN1612
5825
5823
5825
5824
33
FU1
FU2
FUSE HOLDER, L I T T L E F U S E 342004
FUSE HOLDER, L I T T L E F U S E 342004
HS1
HS2
HS3
HEATSINK, WAKEFIELD ENG., MODEL 6 9 0 - 3 - B A
H E A T S I N K . ( C R 2 8 ) , WAKEFIELD ENG., MODEL 6 9 5 - B
HEATSINK ( C R 2 9 ) , WAKEFIELD ENG., MODEL 6 9 5 - B
J1
J5
J6
5 P I N SENSOR SOCKET, AMPHENOL 126-218
5 P I N SENSOR SOCKET, AMPHENOL 126-218
7 P I N REMOTE S E T P O I N T , AMPHENOL 126-198
HEATER BINDING P O S T , E . F . JOHNSON, 111-0113-001
HEATER BINDING P O S T , E . F . JOHNSON, 111-0103-001
C H A S S I S GROUND P O S T , E . F . JOHNSON, 111-0103-001
T1
POWER TRANSFORMER
NE
P I L O T L I G H T , I N D U S T R I A L DEVICES 1 0 4 0 A 8 7
M1
M2
NULL METER
-100-0-100 M i c r o A m p
CURRENT METER
0-1 M i l l i A m p
DL1
DL2
10 TURN D I A L FOR R 3 8 , H E L I P O T 2607
10 TURN D I A L FOR R 1 1 9 , H E L I P O T 2607
J2
J3
J4
T-25-29
34
35
36