Download Model DTC-500_1972

User’s Manual
Model DTC-500
Cryogenic Termperature
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 U S . 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
consequential damages in connection with furnishing, performance, or use of this material.
Obsolete Manual
1972
Table o f Contents
Section
I.
II.
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
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 Installation
2.6 Repackaging f o r Shipment
5
5
5
5
7
7
2.1
III.
IV.
V.
VI.
Page
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
Theory o f Operation
4.1 Introduction
4.2 Detailed Description
( a ) Regulated Power Supplied
(b) Diode Constant Current Supply
( c ) S e t P o i n t Voltage Supply and Divider
(d) V a r i a b l e Gain Amplifier
(e) Automatic Reset C i r c u i t , Bounding C i r c u i t
( f ) Output Power Amplifier
(g) Manual Heater Current Control
(h) Heater Current Metering and Limiting
9
9
13
13
16
17
17
18
21
22
22
25
25
25
26
27
27
27
28
Maintenance and Trouble Shooting
5.1 I n t r o d u c t i o n
5.2 T e s t Equipment and Accessories
5 . 3 General Remarks
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
5.5 O p e r a t i o n a l Checks
5.6 Normal O p e r a t i n g Voltages and Gains
5 . 7 C a l i b r a t i o n o f S e t Point Voltage
5 . 8 C a l i b r a t i o n o f Sensor Current
5.9 Parts List, P r i n t e d C i r c u i t Board Component
Locator and Schematic
29
29
29
30
30
31
32
32
Appendixes
40
33
i
iv
SECTION I
General I n formation
1.1 I n t r o d u c t i o n
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 i s designed t o accept a v o l t a g e signal from a t e m p e r a t u r e
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 s e t 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 t e m p e r a t u r e
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 o f thermal system
parameters.
The o u t p u t power a m p l i f i e r i s 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. In view o f t h e h i g h 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
b e planned t o limit 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
Power boosters 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
t e n watts.
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 of t h e DTC-500 C o n t r o l l e r i s as a
constant temperature r e g u l a t o r f o r laboratory 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 i n c r e m e n t a l
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 of 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 temperature 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 b e 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 s e t 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 i s z e r o , t h e output
v o l t a g e o f t h e t e m p e r a t u r e s e n s o r i s a c c u r a t e l y o b t a i n e d . 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 give
i t s temperature.
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 with 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 :
Sensor
-
Sensor I n p u t
-
f o u r terminal connection, c o n s t a n t
current, potentiometric
10 microamperes
I n p u t Line Voltage
-
115V o r 220V, 50-60 Hz
Power Consumption
-
30VA
C i r c u i t Design
-
Solid S t a t e
Weight
-
15 pounds
Dimensions
- 5¼"
C o n t r o l l e r Range
Heater Output
S e n s o r Current
1°K t o 400°K nominal
10-3 t o 10 watts, 0-1 Amp, 0-10 Volts
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 diodes, single-ended o r
f l o a t i n g model
h i g h , 19" wide, 11½ deep, r a c k
mounting
-
3 Amps/millivolt i n t o 10 ohm r e s i s t o r
a t maximum s e t t i n g
Set Points
-
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
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 0.1 mV g r a d u a t i o n s ,
0.1% l i n e a r i t y
Repeatability
-
±10 m i c r o v o l t s (0.01°K o r b e t t e r )
Automatic Reset
-
3 t o 100 second v a r i a b l e time
constant, o r off
Gain
Temperature Control :
2
Manual Output Control Range
-
10 t u r n p o t e n t i o m e t e r c o n t r o l ,
0 t o f u l l range c u r r e n t
He ate r Current Ranges
Heater Resistance f o r
Max Power
C o n t r o l l e r P r o p o r t i o n a l Gain
-
10 mA, 30mA, 100M, 300mA, 1 A
-
10 Ohms
3 Amps/mV i n automatic mode
(nominal)
Temperature Readout :
( 2 Sensor connections, 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 temperature s e n s i n g only s e n s o r )
Accuracy
-
E x c i t a t i o n Current
-
E x c i t a t i o n Current Regulation
Sensor C a l i b r a t i o n Chart
1.4
-
e q u i v a l e n t t o 100 m i c r o v o l t s (0.1°K
worse c a s e ) ± c a l i b r a t i o n e r r o r o f
sensor
10 microamperes
0.05%
must b e s u p p l i e d by manufacturer
of s e n s o r i n use.
Major Assemblies Supplied
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, Operating and S e r v i c e Manual
(2)
2 , Five p i n p l u g s f o r temperature 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 set p o i n t c a b l e
Temperature s e n s i t i v e diodes are n o t s u p p l i e d as p a r t o f t h e DTC-500 C o n t r o l l e r .
1.5
Accessory Equipment and Custom Options A v a i l a b l e
The following accessory equipment and custom o p t i o n s are 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 of 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)
E x t r a 5 and 7 p i n connectors.
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 set 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 of 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 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 of 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 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 laboratory
calibration service f o r
c o r r e l a t i n g diode o u t p u t v o l t a g e w i t h d i o d e temperature. See
sensors 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 B o o s t e r s f o r h e a t e r power requirements i n e x c e s s of 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 information 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 o f t h e Model DTC-500 Cryogenic Temperature
C o n t r o l l e r . Included are 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 groundi n g requirements, i n s t a l l a t i o n information 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 instrument 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 b e free from mars and s c r a t c h e s , 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 instrument should be 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 use 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 m a t e r i a l s . I f t h e r e i s damage t o t h e i n s t r u ment i n t r a n s i t , be s u r e t o f i l e a p p r o p r i a t e claims with 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 . I n 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 Cryotronics
warranty i s given on page i i .
2.3
Power Requirements
Before connecting 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) is 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 be used. Examine t h e power l i n e f u s e , FU1, (Key No 1 3 , Page 11)
t o i n s u r e t h a t i t 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 = Amp, 230V = 0.4 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 60 112.
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 personnel , t h e National E l e c t r i c a l Manufacturers '
Assocation (NEMA) recommends and some l o c a l codes r e q u i r e instrument
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
three-conductor 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 i s 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 be rack mounted i n c l o s e proximity
t o o t h e r equipment i n dead a i r spaces. However, t h e h e a t from such a d j a c e n t
equipment should not 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 tempera t u r e i n excess o f 5O°C (122°F). As w i t h any p r e c i s i o n i n s t r u m e n t , i t should
not be 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 diode and h e a t e r element
are given i n Figure 2 . 1 ( a ) and ( b ) . The use 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 loops. I f thermal c o n s i d e r a t i o n s d i c t a t e , t h e a l t e r n a t e w i r i n g scheme shown i n Fig. 2 . 1 (c) may be used f o r t h e diode.
The h e a t i n g element should be 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
o f t h e h e a t e r c u r r e n t being conducted i n t o t h e d i o d e s e n s o r l e a d s . E l e c t r i c a l
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 temperature 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 F U 2 , (Key No. 15, Pg. 11) f o r p r o p e r value.
( 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 . ) This f u s e p r o t e c t s
t h e output a m p l i f i e r from damage i n case o f 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 cause damage t o t h e instrument and i n v a l i d a t e s t h e instrument
warranty.
2.6
Repackaging f o r Shipment
Before r e t u r n i n g an instrument 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 preclude 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 i s elsewhere. I f 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 instrument a f t e r t h e s e t e s t s , 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 instrument, 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
instrument i t s e l f ( n o t 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 address
(2)
Instrument Model and S e r i a l Number
(3)
Mal f u n c t i o n 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 instrument 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 with paper o r nylon t a p e . A f f i x mailing 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 instrument i n w a t e r
p r o o f p a p e r o r 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 instrument 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 . Place 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.
8
SECTION I I I
Operating I n s t r u c t i o n s
3.1
Introduction
This 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 techniques. These i n s t r u c t i o n s
are p r e d i c a t e d upon t h e instrument 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 F i g . 2 . 1 (a) i n p a r t i c u l a r
must b e 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
is assumed t o b e connected t o t h e "Heater" t e r m i n a l s as shown i n F i g . 2.1 ( b ) .
3.2
C o n t r o l s , I n d i c a t o r s and Connectors
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 a r e keyed t o t h e e n t r i e s i n
Table 3.1.
Table 3.1
NO. KEY
1
2
FUNCTION
NAME
SET POINT
0 - 0.1
-
VOLTS
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 adjust
s e t 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 .
Kelvin-Varley d i v i d e r , s e l e c t s most
s i g n i f i c a n t d i g i t s o f setpoint voltage.
3
VOLTS
SET POINT
0 t o .9 VOLTS
4
GAIN 1
5
AUTO- RESET
OFF, MIN. - MAX.
Adjusts gain o f amplifier f o l l o w i n g
i n t e g r a t o r . (See Fig. 3.3) E f f e c t i v e l y determines time c o n s t a n t o f
i n t e g r a t o r between 3 and 100 seconds.
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
readout o f s e n s o r A v o l t a g e . MAN. B
p e r m i t s readout o f s e n s o r B voltage;
-
100
S e l e c t o r s w i t c h o f Kelvin Varley
divider 0.1 volt per step
Adjusts o v e r a l l c o n t r o l l e r gain
( F i g u r e 3.3)
between 330 and 33,000.
9
Table 3.1 ( c o n t . )
NAME
FUNCTION
7
MAN. RESET
When mode s e l e c t o r s w i t c h (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 mits 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 l i m i t e r . Use
o f 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.
9
POWER
A. C.
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
s c a l e d e f l e c t i o n corresponds t o MAX.
HEATER
switch ( ) s e t t i n g .
NO. KEY
l i n e s w i t c h (ON/OFF)
.
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 s e t 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 i s non- l i n e a r
for large errors of e i t h e r sign.
13
115 /2 30V
50-60 HZ
A. C.
14
¼A
A. C.
l i n e f u s e (FU1).
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
(Five p i n ,
Sensor A c a b l e r e c e p t a c l e .
Amphenol t y p e 126-217 Plug)
18
SENSOR B
Sensor R c a b l e r e c e p t a c l e . ( F i v e p i n ,
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 e x t e r n a l d i v i d e r
f o r comparison w i t h s e n s o r v o l t a g e .
Front p a n e l s e t 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 s w i t c h 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 set on "INTERNAL"s i n c e i t s l o c a t i o n
on t h e rear 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 out t h e i n s t r u m e n t .
S. B.
l i n e voltage s e l e c t o r s l i d e
switch
See p a r a . 2 . 3
10
11
12
T a b l e 3.1
(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 h i g h s i d e and Black
i s t h e low s i d e ) .
22
GROUND
C h a s s i s ground t e r m i n a l
NO. KEY
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 as a c r y o g e n i c thermometer t o measure t h e t e m p e r a t u r e
of 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 follows:
(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 WAN. A".
(3)
"MAN. RESET" (Key
(4)
"MAX. HEATER-AMP."
(5)
"GAIN" (Key No. 4) t o minimum s e t t i n g ,
(6)
"AUTO RESET" (Key No. 5) t o o f f .
No. 7) t o zero.
(Key No, 8) t o 0.01.
(7) "POWER'' 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 off 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 is t o t h e l e f t , t h e
s e t p o i n t voltage i s l e s s than t h e sensor voltage. If t h e d e f l e c t i o n i s 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 the left. 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 ) to 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 , so 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 d e t e r m i n i n g t h e s e t p o i n t v o l t a g e , r e f e r t o t h e diode 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 diode i s i n u s e as d e s c r i b e d i n paragraph
3 . 4 . To maintain 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 d e s i r e d 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 b l o c k 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 s e t 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 be 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
s h o u l d 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 s h o u l d s t a r t 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 g a i n i s i n c r e a s e d . As t h e sample h o l d e r temperature 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 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 value 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 gain u n t i l an incremental change
i n gain 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" gain 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 . As
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
with 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.
As 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 maintain t h e
sample a t t h e lower temperature r e q u e s t e d . The NULL METER should r e a d zero
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 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 . The
NULL meter s h o u l d d e f l e c t t o t h e l e f t and t h e HEATER CURRENT meter should
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 will d e c r e a s e toward
i t s new s t e a d y s t a t e v a l u e . A s t h e NULL meter c e n t e r s , t h e HEATER CURRENT
should s t a b i l i z e a t 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
temperature.
A s k e t c h o f 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 temperature 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 are p r o p e r l y a d j u s t e d . (This s t a t e ment presupposes t h a t t h e sample h o l d e r may be a c c u r a t e l y modeled as a simple
R-C t y p e time c o n s t a n t c i r c u i t . )
I f o s c i l l a t i o n o r overshoot a r e observed when changing t h e s e t p o i n t
v o l t a g e i n small i n c r e m e n t s , reduce t h e G A I N and AUTO RESET 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.
3.6
Manual 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
MAN. A o r MAN. B, a c o n s t a n t c u r r e n t may b e 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
switch s e t t i n g .
3.7
Temperature Readout Mode (Sensor B)
I n some a p p l i c a t i o n s , t h e t e m p e r a t u r e 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 i t i s d e s i r e d t o measure t h e temperature 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 tempera 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 only t h e
t e m p e r a t u r e i s t o b e measured. Sensor B must be c a l i b r a t e d .
Assume t h a t t h e t e m p e r a t u r e a t Sensor A has 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 temperature c o n t r o l mode a s 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
17
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 hold t h e temperature s t e a d y i n t h e MAN A p o s i t i o n . Then
switch 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 zero t h e NULL meter. This r e a d i n g i s used t o determine
t h e temperature o f Sensor B. After t a k i n g t h e Sensor B v o l t a g e r e a d i n g ,
r e s e 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 t h e d e s i r e d temperature
c o n t r o l p o i n t and then 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 is 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 of 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 o f time.
3.8
Remote Temperature Programming
Remote temperature 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 o f J should be
equal t o 515 ohms. The remote s e t p o i n t connection diagram i s shown i n
Figure 3.5.
Equivalent S e t P o i n t Network
Shield
Figure 3.5
18
A number o f e x t e r n a l temperature programming networks a r e shown i n
Figure 3 . 6 .
TRIM
Figure 3 . 6
The following i s a s u g g e s t e d procedure f o r designing e x t e r n a l temperature
s e t point control c i r c u i t r y :
1.
Determine t h e range of 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 :
a,)
Temperature c o n t r o l range
19
c.)
Fixed temperature s e t 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 c o n t i n u o u s l y v a r i a b l e t e m p e r a t u r e s e t
points.
A d d i t i o n a l 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 i n t e n d e d
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 of 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 of t h e c o r r e c t v a l u e t o
develop a drop o f 3 v o l t s , it i s s u g g e s t e d 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 approximately 20 ohms p e r 0 . 1 v o l t s
and a s h u n t i n g r e s i s t o r (R1 i n F i g . 3 . 6 a) used f o r p r e c i s i o n
trimming.
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 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 s e t p o i n t
v o l t s s w i t c h and 10 t u r n d i a l as f o l l o w s :
a.)
Connect a p r e c i s i o n 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 A-B of t h e s e n s o r A i n p u t p l u g J (amphenal 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 of t h e s e n s o r as shown i n
Fig. 3 . 7 , and t u r n 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 t o Manual A p o s i t i o n .
Shield
Figure 3 . 7
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 e q u a l t o 10 x 10-6 x R v o l t s ,
t h u s a 100K 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
reformer "TEMPERATURE SET POINT'' s w i t c h on t h e r e a r of 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 zero e r r o r when
t h e i n t e r n a l temperature s e t p o i n t s w i t c h on t h e f r o n t p a n e l i s a t
1.000 v o l t s . I n c r e a s e t h e gain t o maximum and a d j u s t t h e 10 t u r n
d i a l a t t h e i n t e r n a l s e t p o i n t c o n t r o l if 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 s w i t c h on t h e
r e a r 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 R on t h e
e x t e r n a l set p o i n t programming instrument s o t h a t t h e n u l l meter r e a d s
zero.
The external 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 . In t h a t c a s e , a p r e c i s i o n
r e s i s t a n c e d i v i d e r may b e used f o r R i n t h e s e n s o r i n p u t c o n n e c t o r ,
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 b e s h i e l d e d
20
and the shields connected to pin H of the sensor A input connector
(J1). Similarly, the leads and box housing the externally programmable
temperature resistance network should be shielded through pin H
of external set point plug (J3).
3.9
Grounding
The chassis is grounded by the 3 lead power cable t o the electrical
supply common ground. The common lead of the controller circuitry ("Lo"
terminal of the heater output - Key 21, Fig. 3.2) is externally connected
to the chassis ground terminal. Although the grounding of the controller
common is normal operation practice, the common "Lo" terminal may be
disconnected from chassis ground if doing so helps to eliminate accidental
ground loops within the system.
21
SECTION IV
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 of 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 Figure 3.3 and Figure 5 . 2 a s an a i d i n t h e following 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 c u r r e n t t o flow through t h e s e n s o r diode. The set 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 ( o r
e r r o r ) s i g n a l i s a m p l i f i e d i n a v a r i a b l e gain amplifier s t a g e ( o p e r a t i o n a l ampliThe amplified 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
f i e r A2 i n Fig. 5 . 1 ) .
a p p l i e d t o (1) a gain o f 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 output o f 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 gain a m p l i f i e r whose gain
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 gain 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
gain o f 2 0 a m p l i f i e r are a s s o c i a t e d with 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 Q 1
and f i e l d e f f e c t t r a n s i s t o r 4 2 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 output 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 2 . Operational a m p l i f i e r
A4 and t r a n s i s t o r s 4 3 and 44 i n Fig. 5.1 comprise t h e power a m p l i f i e r . The output
o f t h e power a m p l i f i e r i s 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 by p r o v i d i n g a thermal
s i g n a l 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.
T o i l l u s t r a t e t h e automatic temperature c o n t r o l a c t i o n , suppose t h e s e n s i n g
diode i s c o l d e r t h a n t h e programmed temperature s e t t i n g . The diode 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 g r e a t l y
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 raises
t h e diode temperature and reduces i t s v o l t a g e . As t h e diode temperature 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 temperature 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
diode t o maintain 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 i s used t o reduce t h i s e r r o r t o zero. The automatic reset
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 output 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 continues 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 response t o t h e i n t e g r a t o r s i g n a l .
Eventually t h e e r r o r i s d r i v e n t o zero 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
value. 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 of h e a t e r c u r r e n t r e q u i r e d t o maintain
t h e e r r o r a t z e r o , 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 temperature coincidence between
t h e diode and t h e s e t p o i n t temperature. 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 zero t o one,
*"Feedback Control System Analysis and Synthesis" by John J . D ' A Z Z O and Constantine
H. Houpis, McGraw-Hill Book Co., N e w York, 1966, P g . 397.
22
23
FIGURE 4.2
SIMPLIFIED EQUIVALENT CIRCUIT OF
AUTOMATIC RESET AMPLIFIER
24
4.3
Detailed Description
(a)
Regulated Power S u p p l i e s
There are f i v e , e s s e n t i a l l y i d e n t i c a l , r e g u l a t e d power s u p p l i e s i n t h e
instrument. They are d e s i g n a t e d as PS-1 through PS-5 i n Figure 5.1. Each
supply uses an i n t e g r a t e d uA723 t y p e P r e c i s i o n Voltage Regulator as i t s main
component. A d e t a i l e d drawing o f one o f t h e s u p p l i e s i s given i n F i g . 4 . 1 .
A d e s c r i p t i o n o f t h i s supply should s u f f i c e f o r a l l t h e o t h e r s .
The secondary v o l t a g e of t r a n s f o r m e r T 1 appearing a t t e r m i n a l s 1 4 and 15
i s r e c t i f i e d by diode r e c t i f i e r b r i d g e CR1-4 and f i l t e r e d by c a p a c i t o r C 1 .
This u n r e g u l a t e d v o l t a g e i s a p p l i e d t o t h e uA723 power supply l e a d s 1 2 and 7 .
The r e f e r e n c e v o l t a g e op-amp i n t h e uA723 produces a s t a b l e , 7 . 1 v o l t r e f e r e n c e
v o l t a g e a t p i n 6. This v o l t a g e i s e x t e r n a l l y coupled t o t h e non-inverting i n p u t
t o t h e r e g u l a t o r op-amp. (pin 5 ) by r e s i s t o r R 1 . The value o f R i s chosen t o
be equal t o t h e p a r a l l e l combination o f R3 and R4 t o minimize o f f s e t e r r o r s .
R e s i s t o r s R3 and R4 sample a f r a c t i o n o f t h e o u t p u t v o l t a g e and apply i t t o
t h e i n v e r t i n g i n p u t , p i n 4. The r e g u l a t o r op-amp a t t e m p t s t o maintain t h e
p o t e n t i a l at p i n s 4 and 5 equal t o one a n o t h e r i n s p i t e o f v a r i a t i o n s i n t h e
l i n e v o l t a g e and load c u r r e n t . The output c u r r e n t i s passed through R2. Automatic
c u r r e n t l i m i t i n g i s accomplished by c u r r e n t sampling r e s i s t o r R 2 and t h e c u r r e n t
s h u t down t r a n s i s t o r connected t o p i n s 2 and 3. I f t h e c u r r e n t through R 2 i s
e x c e s s i v e , t h e r e s u l t i n g v o l t a g e developed a c r o s s R2 causes t h e t r a n s i s t o r t o
conduct, d i v e r t i n g base c u r r e n t from t h e s e r i e s p a s s t r a n s i s t o r .
(b)
Diode Constant Current Supply
R e f e r r i n g t o Fig. 5.1, power s u p p l i e s PS-1 and PS-2, and o p e r a t i o n a l
a m p l i f i e r 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 of t h e o p e r a t i o n a l a m p l i f i e r A1, t h e diode
c u r r e n t i s forced t o flow through r e s i s t o r R26 developing 4.99V a t 10 uAmps.
The wiper o f p o t e n t i o m e t e r R23 i s p o s i t i o n e d S O t h a t an equal v o l t a g e i s developed
between t h e w i p e r o f R23 and t h e j u n c t i o n of CR-22A and R24. With t h e wiper s o
a d j u s t e d , any v a r i a t i o n i n t h e diode c u r r e n t w i l l r e s u l t i n a d i f f e r e n t i a l e r r o r
v o l t a g e . When a m p l i f i e d and a p p l i e d t o t h e cathode o f t h e s e n s o r diode, t h i s
s i g n a l will b e o f such a p o l a r i t y as t o d r i v e t h e diode c u r r e n t back towards i t s
design v a l u e o f 10 uAmps.
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 Point Voltage Supply and Divider
F l o a t i n g power supply PS-3 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-13. 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 CR-13 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, R117, R28, R29, R33 and R34. The s e t 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 R28.
The f l o a t i n g s e t 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 s e t p o i n t v o l t a g e 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.
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(d)
Variable Gain A m p l i f i e r
The v a r i a b l e g a i n a m p l i f i e r shown i n F i g . 3 . 3 , w i t h a g a i n range o f 7 . 5 t o
750 , 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 amplifier A2. The i n p u t
r e s i s t o r i s R32 and t h e feedback element c o n s i s t s o f R35 and R41 and p o t e n t i o m e t e r
R37 and R38 and r e s i s t o r s R39, R40 and R 4 1 .
Diodes CR-26, 2 7 , 2 8 , 29 o r R39 and R40 comprise a s o f t - l i m i t e r 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 r e s i s t a n c e 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 o f a m p l i f i e r A2 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 . As t h e e r r o r
amplitude i n c r e a s e s , e i t h e r diode CR-35 o r CR-36 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 l i n e a r 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 60% o f f u l l scale.
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( e ) 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 , i n t e g r a t o r , v a r i a b l e gain a m p l i f i e r (Av o f 1 t o
1 0 0 ) , and t h e c o n s t a n t gain o f 20 a m p l i f i e r shown i n F i g . 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 of t h e s t a g e i s given i n
Fig. 4 . 2 .
A p p l i c a t i o n o f 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
z e r o 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 o f t h e s t a g e . The c o n s t a n t gain of
20 amplifier i n Fig. 3.3 is r e p r e s e n t e d by t h e term R57/R45 while t h e v a r i a b l e
gain 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 + R57/Re)/R45C20 i n t h e e q u a t i o n i n Fig. 4 . 2 .
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 capac i t o r C20 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 C20. 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 C17 is o f
such a p o l a r i t y as 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-33
conducts reducing t h e e f f e c t i v e gain o f t h e s t a g e 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 occurs if t h e e r r o r s i g n a l a t t h e base 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-30 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 42 i s c u t - o f f (approximately -9V) at t h e g a t e . As t h e base o f Q1 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 i t s source-drain impedance t o
a c t as 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 C20. This 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 t y p e zero a c t i o n .
The switch S3 i s open 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 .
(f)
Output Power Amplifier
The processed e r r o r s i g n a l appearing a t TP18 is 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 s e r i e s 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 w i t h op-amp A4, R65 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 R62 s o 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 R65/R62 o r approximately 3.5.
A t r a t e d output c u r r e n t o f one ampere, t h e v o l t a g e appearing a t TP20 i s -10.5
v o l t s . Use o f 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 will 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.
Winding 5-6-7 on t r a n s f o r m e r T1, diodes CR-22 and CR-23 and c a p a c i t o r C16
c o n s t i t u t e s t h e power supply f o r t h e s e r i e s p a s s elements 4 3 and 44.
Power s u p p l i e s PS-4 and PS-5 are s u p p l i e s f o r o p e r a t i o n a l a m p l i f i e r s A 2 ,
A3 and A4, t r a n s i s t o r 41 and FET 42.
(g)
Manual He a t e r Current Control
When t h e mode s e l e c t o r switch is set t o e i t h e r MAN A o r MAN B p o s i t i o n ,
switch s e c t i o n S1-F connects t h e i n p u t o f t h e power a m p l i f i e r s t a g e t o t h e wiper
27
o f p o t e n t i o m e t e r R54. 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 -10 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 R54 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 .
(h)
t i e a t e r 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 output c u r r e n t i s determined by t h e s e r i e s combinat i o n o f t h e h e a t e r element r e s i s t a n c e and one of t h e group of r e s i s t o r s R206
through R209. T h i s s e r i e s combination i s 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
IMA c u r r e n t meter and R66.
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 attempt t o achieve 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 resistance 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 warranty and i s l i k e l y t o damage t h e o u t p u t power
amplifier circuit.
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SECTION V
Maintenance and Troubleshooting
5.1
Introduction
T h i s 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 s c h e m a t i c 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
T e s t Equipment and Accessories
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 high 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 c o n n e c t o r
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 of 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 it 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
of 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 of 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 c r y o g e n i c system
before t e s t i n g t h e c o n t r o l l e r proper.
(1)
(2)
(3)
(4)
(5)
Some s u g g e s t e d checks a r e :
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 loss of 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 blocks 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 high 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 be avoided.
Examine h e a t e r element f u s e FU2.
I f 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 is m a l f u n c t i o n i n g 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
29
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 m a t e r i a l s 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 b o a r d , t h e r e
is always t h e r i s k of l i f t i n g a c o n n e c t i o n 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 is 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 last 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 b o a r d , 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 b o a r d , unscrew t h e b o l t s from t h e bottom o f t h e case
which attach 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 r e a r 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 is s t r e s s e d , it 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 watts) 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
heat 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 a p p l y 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 o f 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 wick 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 a r e a w i t h warm 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 c o n n e c t o r p l u g with 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
p l a c e a t e n watt, t e n ohm
t e s t p l u g . Remove t h e h e a t e r element l e a d s
r e s i s t o r across the heater output terminals.
and
Ten microamperes flowing through t h e test 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
is 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 .
30
W h i l e 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 z e r o towards i t s maximum.
T h e 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 with t h e advance o f t h e
MAN RESET c o n t r o l .
With t h e MAW 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 of t h e p o s i t i o n s .
Zero t h e n u l l meter with 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 . Turn t h e
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 switch t o AUTO A .
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 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. 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 r i s e
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 will g r a d u a l l y rise towards f u l l s c a l e 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 i s determined by t h e AUTO RESET time c o n s t a n t
s e t t i n g . The r a t e 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 .
AUTO RESET and GAIN c o n t r o l s t o mid-scale 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. The HEATER CURRENT meter should gradu a l l y d e c r e a s e from f u l l s c a l e 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 zero 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.
I f 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 a r e given i n
Section 5.6.
5.6
Nominal Voltages and Gains
The following v o l t a g e measurements were made with an RCA S e n i o r Voltohmist
meter. A 1%, 75K 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 w a t t 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 4 , C7, C10 and C13 i n
power s u p p l i e s PS-1 through PS-5 nominally 24 v o l t s with nominal l i n e v o l t a g e .
The output v o l t a g e which appears between t e r m i n a l s 3 and 7 o f t h e uA723
i n t e g r a t e d c i r c u i t s i s 15 v o l t s . The sampling r e s i s t o r s a r e p r o p o r t i o n a l
s o t h a t t h e p o t e n t i a l between p i n 4 and p i n 7 i s approximately 7 v o l t s .
Reference diodes CR-37 and CR-13 a r e 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 C16 i n PS-6 v a r i e s between
approximately 1 4 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 l o a d 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 o u t p u t .
31
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
o f Q1.
The o u t p u t power a m p l i f i e r s t a g e may be checked 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 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 R54 ( t e r m i n a l s
6 t o 7) i s 3.4 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 he 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 o f R51 and ground. The
v o l t a g e a t t h e o u t p u t o f a m p l i f i e r A 4 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 base e m i t t e r drops o f Q3 and 44.
With t h e AUTO RESET c o n t r o l i n t h e o f f 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 s w i t c h 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 g a i n
o f a m p l i f i e r s A3 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 scale 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
o f t h e incremental output 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 gain. The nominal cascade g a i n of
t h e last two s t a g e s i s 40.
Gain checks should be performed by f i r s t z e r o i n g t h e NULL meter w i t h t h e
SET POINT VOLTAGE VERNIER. A small v o l t a g e change i s 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 Point Voltage
The instrument 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 mV and r e s i d u a l
b a s e l i n e r e s i s t a n c e o f t h e 10 t u r n p o t e n t i o m e t e r R28. Should i t b e d e s i r a b l e
t o check o r r e c a l i b r a t e t h e s e t 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
d i s c o n n e c t e d and t h e "TEMPERATURE SET POINT" switch 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 be measured a c r o s s p i n s E-D
o f t h e s e n s o r connectors J1 o r J 2 without opening t h e core. Voltage measurements
s h o u l d be t a k e n with 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 i n s t r u m e n t . 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 , remove t h e
cover and a d j u s t trimmer R33 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 should
be w i t h i n 3.0000 ±100 uV.
5.8
C a l i b r a t i o n of 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
± 1 0 nanoamperes. To check t h e s e n s o r c u r r e n t without removing t h e case 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 of not l e s s t h a n .01% t o l e r a n c e
should b e connected t o p i n s A-B of 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" s w i t c h on t h e r e a r p a n e l should be
switched t o "REMOTE".
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 e q u a l t o 10 microamperes times t h e v a l u e o f t h e
r e s i s t o r . T y p i c a l l y , a 100K ±.01% r e s i s t o r should read 1.0000 w i t h i n 100 microv 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 drop 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 b e measured, a f t e r removing t h e c a s e cover and a d j u s t i n g trimmer
R23 on t h e c i r c u i t board.
32
5.9
Parts List, Component L o c a t i o n Diagram and S c h e m a t i c
Table 5.1
PARTS LIST
R1
R2
R3
R4
R5
R6
R7
R8
R9
R10
R11
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22
R23
R24
R25
R26
R27
R28
R29
R30
R31
R32
R33
R34
R34A
R35
R36
R37
R38
R39
R40
R41
R42
3.6K
1/4W
10%
6 . 2 ohms
1/4W
5%
8.2K
1/8W
1%
7.5K
1/8W
1%
3.6K
1/4W
10%
6 . 2 ohms
1/4W
5%
8.2K
1/8W
1%
7.5K
1/8W
1%
3.6K
1/4W
10%
1/4W
5%
6 . 2 ohms
8.2K
1/8W
1%
7.5K
1/8W
1%
1.24K
1/8W
1%
3.6K
1/4w
10%
5%
6.2 ohms
1/4W
1/8W
1%
8.2K
7.5K
1/8N
1%
3.6K
1/4W
10%
6 . 2 ohms
1/4W
5%
8.2K
1/8W
1%
7.5K
1/8W
1%
7.5K
1/8W
1%
5K TRIMPOT, HELIPOT
58PR5000
30.9K
1/8W
1%
1/8W
1%
50K
499K
1/8W
.1%
100K
1/4W
5%
100 ohms 1 0 TURN POT.
HELIPOT 7226
TRIM RESISTOR
3.48K
1/8W
1%
4 70
1/8W
1%
100K
1/4W
5%
10 TRIMPOT, HELIPOT
78PR10
5 79
1%
1/4W
(NOMINAL)
(NOMINAL)
(NOMINAL)
(NOMINAL)
(NOMINAL)
(NOMINAL)
(NOMINAL)
(NOMINAL)
22 MEG
1/4W
560
1/4W
10K POTENTIOMETER
100
1/8W
100
1/4W
10K
1/4W
20K
1/4W
5%
5%
( G A I N CONTROL)
1%
5%
5%
5%
(NOMINAL)
33
R43
R44
R45
R46
R47
R48
(NOMINAL)
R50
R51
R52
R53
R54
R55
R56
R57
R58
R59
R60
R61
R62
R63
R64
R65
470
1/4W
330K
1/4W
8.65K
1/8W
18K
1/4W
100K
1/4W
1.5K
1/4W
12K
1/4W
33K
1/4W
680K
1/4W
1/4W
2 . 7 PEG
1 K TEN TURN POT
3.83K
1/8W
2.7K
1/4W
1 MEG
1/4W
1.2K
1/4W
1 MEG POT
1K
1/4W
10K
1/4W
16.2K
1/4W
50K
1/8W
12K
1/4W
56K
1/4W
R101-104
R105-106
R107-117
17.61
1/8W
TRIMMING RESISTORS
45.7
1/8W
R200
R201
R202
R203
R204
R205
R206
R207
R208
R209
430
54.9
16.9
5.0
1.65
4.995
1000
324
90
23.33
R49
1/8W
1/4W
1/8W
1/8W
1/2W
1W
1/4W
1/2W
2W
5W
5%
5%
1%
5%
5%
5%
5%
5%
5%
5%
(MANUAL RESET)
1%
5%
5%
5%
(AUTO RESET CONTROL)
5%
5%
1%
1%
5%
5%
.05%
.05%
1%
1%
1%
1%
1%
1%
1%
1%
1%
1%
(NOMINAL)
SET POINT
VOLTAGE D I V I D E R
ASSEMBLY
HEATER CURRENT
RANGE AND
METER SWITCH
ASSEMBLY
34
c1
c2
c3
c4
c5
C6
c7
C8
C9
c10
c11
c12
C13
C14
c15
C16
C17
C18
C19
c20
c21
c22
220 MFD, 6 3 VDC, E l e c t r o l y t i c
31 pf:
Mica
DM10
OPTIONAL 25 MFD, 25 VDC, E l e c t r o l y t i c
220 MFD, 63 VDC, E l e c t r o l y t i c
91 pF
Mica
DM10
OPTIONAL 25 MFD, 25 VDC, E l e c t r o l y t i c
220 MFD, 63 VDC, E l e c t r o l y t i c
9 1 pF
M i ca
DM10
OPTIONAL 25 MFD, 25 VDC, E l e c t r o l y t i c
220 MFD, 6 3 VDC, E l e c t r o l y t i c
9 1 pF
Mica
DM10
OPTIONAL 25 MFD, 25 VDC, E l e c t r o l y t i c
220 NFD, 63 VDC, E l e c t r o l y t i c
9 1 pF
Mica
DM10
OPTIONAL 25 MFD, 25 VDC, E l e c t r o l y t i c
2500 MFD, 25 VDC, E l e c t r o l y t i c
. 2 2 MFD, 100 VDC, Mylar
. 6 8 MFD, 50 VDC, Mylar
. 2 2 MFD, 50 VDC, M y l a r
100 MFD, 15 VDC, T a n t a l u m
470 pF, 100 VDC, Mica
. 0 1 MFD, 50 VDC, Mylar
CR1-12
CR13
CR14-21
CR22
CR23
CR24
CR25
CR26
CR27
CR28
CR29
CR30
CR31
CR32
CR33
CR34
CR35
CR36
CR37
S I L I C O N RECTI F I ER
REFERENCE DIODE
SILICON RECTIFIER
SILICON RECTIFIER
SILICON R E C T I F I E R
S I L I C O N PROTECTION DIODE
S I L I C O N PROTECTION DIODE
S I L I C O N DIODE
S I L I C O N DIODE
10 V. REFERENCE DIODE
10 V. REFERENCE DIODE
S I L I C O N DIODE
3.9 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
A1
A2
A3
A4
OPERATIONAL
OPERATIONAL
OPERATIONAL
OPERATIONAL
REFERENCE DIODE
AMPLIFIER
AMP L I F I E R
AMPLIFIER
AMP L I F I E R
IN4002
IN4571A
IN4002
IN1612
IN1612
411
411
411
411
IN961
IN961
411
DZ 7011
411
IN841
411
IN358
IN358
IN4571A
5825
5823
5825
5824
35
REG.,
REG.,
REG.,
REG.,
REG.,
6W7723393
6W7723393
6W7723393
6W7723393
6W7728393
M1
M2
M3
M4
M5
VOLT.
VOLT.
VOLT.
VOLT.
VOLT.
Q1
Q2
Q3
Q4
2N3638
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 SWITCH, SWITCHCRAFT 4 6 2 5 6 L F
TEMP. S E T P O I N T SELECTOR SWITCH, SWITCHCRAFT 4 6 2 0 6 L
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
HEATSINK ( C R 6 ) , WAKEFIELD ENG., MODEL 6 9 5 - B
HEATSINK ( C R 7 ) , WAKEFIELD ENG. , MODEL 6 9 5 - B
J1
J2
J3
J4
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 B I N D I N G P O S T , E . F . JOHNSON, 111-0113-001
HEATER B I N D I N G 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
F E T TRANSISTOR
36
T1
POWER TRANS FORMER
PL1
P I L O T L I G H T ASSEMBLY, I N D U S T R I A L DEVICES 1040A87
MT1
MT2
NULL METER
-100-0-100 uAmp.
CURRENT METER
0-1 Milliamp.
DL1
DL2
10 TURN D I A L FOR R28, H E L I P O T
10 TURN D I A L FOR R 5 4 , H E L I P O T
T-25-29
2607
2607
37
38.
39.