Download ST350 Radiation Counter

Page 1
SPECTECH
ST350 Radiation Counter
Operating and Service Manual
November 1994
Spectrum Techniques
Model ST350 RADIATION COUNTER
The ST350 Radiation Counter brings new dimensions to Nuclear
Science instruction and Health Physics training. By incorporating a specialized
microcontroller, many of the features previously found only in multiple
products are now combined in a single inexpensive instrument.
The classical nuclear scaler function has now been extended to include
a timer, preset counter, digital ratemeter with alarm, computer interface and a
battery option for field applications. When constant counting statistics are
required, the preset count mode can be extremely useful and the digital
ratemeter is ideal for contamination survey work. An alarm level may be set to
any pre-selected value and if the count rate exceeds this level, the audible alarm
is sounded warning of a high activity condition.
High voltage is fully variable from 0 to +1200 volts, allowing
operation with many types of GM tubes. The supply is fully regulated and
controlled by the processor for digital accuracy and readout on the display.
Extra large LED's are used for the digital display for clear visual readout under
widely differing ambient light conditions with leading zero suppression for
clarity.
Classroom demonstrations and nuclear experiments may now be run
directly from an IBM-PC compatible computer using the on-line serial
DATALINK built into the ST350 and the standard RADEM emulation
software. All functions of the Radiation Counter are accessible and may be
controlled from the computer, including the high voltage setting for the GM
tube using the optional LABLINK software. The Radiation Counter-PC
software supplied produces computer screen displays of all functions including
analog emulation of the ratemeter mode. Real-time data is automatically
transferred to the computer and stored in spreadsheet compatible files. Data
analysis and graphical presentation is now possible using many common
spreadsheet programs bringing new techniques to Nuclear Science education.
Optional batteries may be installed in the ST350 making the instrument
fully portable. An AC to DC line converter/charger is supplied for continuous
benchtop operation with or without the batteries installed.
Page 2
Specifications.
Page 3
Operation.
Input:
BNC connector. Accepts standard Geiger tubes.
High voltage:
0 to +1200 volts, digitally selectable in 25 volt
increments.
Display:
6-decade LED, 1 in. numerals. Displays counts,
preset counts, time, preset time, CPM, CPS, alarm
level, and high voltage.
Modes:
Audio:
Count for preset time, count for preset count,
counts/min., counts/sec., set alarm level 0-999999
cps, set high voltage 0-1200v,and remote.
Piezo alerter if countrate exceeds preset level.
Data Link:
DB-9 male connector accepts RS-232 serial cable.
Power:
Input 7.5 volt DC, at 500mA from AC line/charger.
Specify 110-120, 220-240 VAC at time of order.
Battery option requires installation of 4 x C size
NiCd rechargeable batteries (not supplied).
Dimensions:
12 in. W, x 8 in. H, x 4.5 in. D.
Software supplied:
ST350 Radiation Counter-PC emulation software.
DOS program runs on most IBM compatible PC's
including CGA, EGA, VGA, SVGA, and Hercules
graphics systems. Real-time display of simulated
analog ratemeter with auto-ranging, digital
ratemeter in CPM or CPS, count, elapsed time,
preset count, preset time, high voltagesetting,
acquisition time, and run number. Data is loaded
into spreadsheet compatible files for transfer.
Bi-directional LABLINK offers full control of all
functions including preset count, preset time,
countrate in CPM or CPS, alarm level, high
voltage, start, stop, reset, and data transfer.
Requires EGA or VGA graphics. All operations
may be run directly from the computer with
spreadsheet compatibility.
CAUTION
Never operate the ST350 Radiation
Counter with the GM probe disconnected. Dangerous voltages can exist at
the probe connector so ensure the instrument is in the OFF position and the high
voltage is set to zero before disconnecting or reconnecting the GM probe.
General.
The ST350 Radiation Counter may be operated with or without the
optional rechargeable batteries installed by connecting the AC power supply/
charger module supplied. If batteries are installed, it may be necessary to supply
an initial overnight charge before operating away from the power source.
A LOW BATTery indicator is included to alert the operator before the
batteries become fully exhausted and the instrument ceases to function. If this
indicator is illuminated, discontinue use until the unit has been reconnected to
the charger. To maintain good battery life and condition, rechargeable batteries
should be discharged and fully recharged periodically.
Detectors.
Geiger-Mueller tubes produce electrical pulses when ionizing radiation
events occur within their sensitive volume. For proper operation, these detectors
should be run at a predetermined operating voltage specified by the manufacturer or derived empirically. To improve sensitivity to alpha and beta particle
radiation, many GM tubes have extremely thin entrance windows which require
considerable care in handling. Do not remove protective caps unless necessary
and never touch the window.
The ST350 is designed to accommodate many types of GM probes and
includes a fully adjustable high voltage power supply to cover a wide range of
applications. The high voltage level may be displayed on the digital readout by
moving the FUNCTION switch to the HIGH VOLTAGE position. Adjustments
to the high voltage may now be made using the UP/DOWN buttons in 25 volt
increments.
Page 4
Operating Modes and Controls.
Each mode may be selected by the DISPLAY FUNCTION switch.
DISPLAY OFF. Turns off the digital display to conserve power. Mainly used
when operating on internal battery power. The ST350 continues to operate in
the last mode selected.
COUNTS. This is the normal operating mode where the display registers the
number of radiation events detected by the GM tube. Before starting a count, a
preset count value or preset time may be entered using the UP/DOWN buttons.
If this feature is selected, once started the unit will continue to count until the
preset count or preset time level is reached. Preset count mode can be very
useful when constant counting statistics are required.
TIME. If the operator wishes to count radiation events for a predetermined
time, select this position and with the unit in the STOP mode enter the required
counting time in seconds using the UP/DOWN buttons. When a preset time is
entered the preset count mode is reset and disabled
RATEMETER. This mode provides a digital display of the instantaneous
count rate. It can be very useful for survey applications particularly when used
in conjunction with the ALARM feature.
ALARM SET. An alarm level in counts per second may be preloaded into the
ST350. Whenever the incoming count rate exceeds this level, an audible alarm
will sound. To select this feature set the FUNCTION switch to ALARM SET
and enter the required level using the UP/DOWN buttons. The ST350 may now
be set to other modes with the alarm level retained.
HIGH VOLTAGE. This position of the function switch displays the value of
the high voltage setting for the GM tube. The high voltage may be adjusted in
25 volt increments using the UP/DOWN buttons between 0 and 1200 volts.
REMOTE. The REMOTE feature is used with the optional LABLINK computer control software. In this mode all front panel control is transferred to the
computer screen. The LED indicators and numerical display will continue to
show mode information being selected by the computer. When using the
standard RADEM emulator software supplied with the ST350, the function
switch may be set to any position.
Page 5
Operation.
Basic operation of the model ST350 Radiation Counter is straightforward and intuitive.
First set the high voltage to the recommended value for the GM tube
using the HIGH VOLTAGE function and the PRESETS buttons.
If no other presets are required, return the function switch to the
COUNT position. Operation may now be controlled with the START, STOP,
and RESET buttons. Setting the function switch to COUNTS will display the
number of radiation events detected by the GM tube, or selecting TIME will
display the acquisition time in seconds.
To count for a preset time, select TIME on the function switch and
enter the required counting time in seconds using the UP/DOWN buttons. Once
set this time will remain until changed with the PRESET. Set the function switch
to COUNTS, press RESET and start the count with the COUNT button. The
count may be interrupted before the preset time is reached by pressing the STOP
button and continued with the COUNT button. Once the preset time is reached
the counter will stop accumulating data. At this point it is only necessary to
press COUNT to restart the next cycle as the preset will automatically be
restored and the count register reset to zero.
Using the preset count mode is similar to the preset time. Set the
function switch to COUNTS and load the preset count value with the UP/
DOWN buttons and press COUNT to start accumulating events. The acquisition
time or the event register may be selected for display using the function switch.
The STOP button may be used to interrupt a count without losing current data.
Once the preset value has been reached, counting will stop automatically. To
recycle simply press COUNT.
In the RATEMETER mode CPS or CPM may be selected using the
UP/DOWN buttons.
Convenient indicator lights show the currently selected mode to assist
operation. An ACTIVITY indicator is also included which monitors incoming
events independent of the selected mode even in the stopped condition.
Page 6
Page 7
GM Plateau.
The correct operating voltage for the Geiger-Mueller tube may be
determined experimentally using a small radioactive source such as Cs-137 or
Co-60. A properly functioning tube will exhibit a "plateau" effect, where the
counting rate remains nearly constant over a range of applied voltage. Place the
radioactive source close to the window of the GM probe and slowly increase the
high voltage until radiation events just begin to be detected. Now increase the
voltage in 25 volt steps recording the counting rate at each increment. The rate
should remain fairly constant over a range of voltage and then increase rapidly
as the high voltage is further raised indicating that the tube is entering the
breakdown region. Do not continue to operate the tube in this breakdown
condition but reduce the high voltage and make a plot of the counting rate
versus the applied voltage. The recommended operating voltage may now be
determined as the center of the plateau region.
Resolving Time.
Geiger-Mueller tube exhibit dead time effects due to the recombination
time of the internal gas ions after the occurrence of an ionizing event. The actual
dead time depends on several factors including the active volume and shape of
the detector and can range from a few microseconds for miniature tubes, to over
1000 microseconds for large volume devices.
When making absolute measurements it is important to compensate for
dead time losses at higher counting rates. If the resolving time of the detector is
known, the true counting rate may be calculated from the measured rate using
the following expression:
n= m/1-mt
where n is the true counting rate, m the measured rate, and t the detector
resolving time.
If the detector resolving time is unknown, it may be determined
experimentally using two radioactive sources. Maintaining constant counting
geometry is important throughout the experiment. A special source split into
two halves is available for making the measurement, but good results may be
obtained by careful positioning of two standard check sources. With the high
voltage correctly set for the GM tube, position the two sources (a+b) side by
side to obtain a count rate of at least 10,000 CPM. Accurately record the
countrate as R(a+b). Remove source (b) and record the count rate as R(a).
Carefully replace source (b) to its original position, remove source (a) and
record the count rate of source (b) as R(b). The resolving time is given by
R(a)+R(b)-R(a+b)
T=
2R(a).R(b)
The resolving time of the ST350 RADIATION COUNTER is very
short and is not a significant factor compared to that of the GM tube.
Page 8
Page 9
Serial Data Link.
Your ST350 Radiation Counter contains a unique Data Link making it
possible to connect the instrument to a personal computer for recording events.
Data transfers are via a RS-232C serial link and requires connection through a
standard 9-pin cable to the computer COM 1 or COM 2 port. The ST350
RADEM Emulation Software may be run directly from the floppy disk supplied,
or copied onto a hard drive if preferred.
To run the software, enter the command line RADEM.EXE. The
program will self configure to the graphics system in use. Select the appropriate
COM port.
At the completion of a preset time, the counting data together with
elapsed time and the computer time of day clock is automatically stored in a
data file which is displayed on the screen as a table. A new count may be
restarted by simply pressing the return key, at which time the data register and
elapsed time will automatically be reset, and the next run started. The counting
may be interrupted at any time and resumed using the return key without loss of
data providing the data is not stored in the data file. To store data in the manual
mode, stop the counting and press the space bar. This action will cause the
registers to reset when counting is restarted.
The ST350 software includes a recycle mode which can be very useful
when performing radioactive decay such as half life experiments or absorption
studies. Use the F1 key to select the required time for each count and the F2 key
to set the number of measurements. Once started, the ST350 will now
automatically store the data at the completion of each counting sequence, reset
the registers, and continue for the number of runs selected.
Data File is a unique and powerful feature of SPECTECH products.
Count and time data is stored in a tab separated temporary file which is
displayed as a table. This may be stored as a .TSV file on the disk at the
completion of a series of measurements. The file is compatible with many
popular spreadsheet programs and may be directly transferred in the spreadsheet
for analysis and viewing. At the end of a series of measurements use the ESC.
key to prompt for file storage. If no filename extension is given the system will
default to .TSV. To simply print the contents of the temporary data file, use the
ALT_P keyboard command.
Your system will now be configured for 9600 Baud data transfer and ready for
use.
Software Emulator.
The ST350 software emulator greatly expands the capability of the
counter by providing large screen displays combined with multi-mode
operation. Three basic modes are included.
Operation of the software is straightforward and requires little explanation.
The analog ratemeter mode provides a large screen display of the
instrument meter which can be very useful for classroom demonstrations of
basic radioactivity. Use the spacebar to switch the display between CPM and
CPS, and the up/down arrows to change the range. For more precise readings,
the digital ratemeter mode may be preferred for some measurements.
When operating in the scaler mode, all radiation events detected by the
GM tube will be recorded during the pre-selected time. Use F1 to initialize the
PRESET TIME mode and enter the required counting time in seconds. Entering
zero or blank will allow the unit to operate in a manual mode. The scaler is
started and stopped using the return key and the elapsed counting time is
displayed in seconds.
Page 10
Applications.
In its basic configuration, battery operation, audible alarm and the
ability to interchange GM probes allows the ST350 to be used for a variety of
applications some of which are listed below.
Surface contamination measurement.
Personnel monitoring.
Page 11
Maintenance.
CAUTION
Dangerous voltages can exist inside the
ST350 from the high voltage power supply.
Before removing the cover ensure the
instrument is in the OFF position and the
high voltage is set to zero. Only qualified
technicians should attempt any repairs.
Plotting a GM plateau.
Radiation background measurement.
Natural radioactivity.
GM resolving time.
Detector efficiency.
Radiation absorption studies.
Backscattering.
Inverse square law.
Isotope half life.
Radiation properties.
Counting statistics.
Low level environmental measurements of naturally occurring
radioactivity may be performed more effectively by surrounding the detector
assembly with 1-2" of lead. This will have the effect of reducing the detector
background, thus improving the lower limit of detection.
Your ST350 has been built with care using quality parts and should not
require any routine service. In the unlikely event of a malfunction, the unit may
be returned to the factory for repair. We will gladly supply a cost estimate if the
warranty period has expired.
Battery installation is straightforward and involves removing the rear
cover which is held in place by four screws. Ensure the instrument is in the
OFF position and the high voltage set to zero! Replacement requires standard
C size Nickel-Cadmium batteries, preferably with a 2000 mAh rating.
A complete list of parts is included for your convenience. Please
contact our customer service department for pricing and availability. In many
instances substitute parts may be used providing they meet or exceed the
original specifications.
Page 12
Page 13
LabLink Communication Software
Your ST350 Radiation Counter is supplied with a computer
communication and control software package named LabLink. Command and
data transfers are via the standard RS 232C serial port, and requires connection
to the computer COM 1 or COM 2 port. LabLink transfers full control of the
ST350 to the computer system and when operating in this mode the function
switch must be set to the REMOTE position and all front panel controls will be
inoperative.
To run LabLink insert the program disk supplied into drive A, type
A:LABLINK and the following screen will appear.
Before commencing a count, ensure the high voltage is set to the
correct value by accessing the PRESETS menu bar and selecting the HIGH
VOLTAGE function. Others presets such as TIME and COUNT may also be set
through this menu.
As with the RADEM software, most operations may be accessed
through the menu bar and are intuitive. Several different VIEW modes are
possible including ratemeter and counter/timer with CPM or CPS selection
For performing plateau measurements, the high voltage may be set to
increase automatically at the completion of each count and the data stored in the
Data File. Use the MODE menu to select this feature.
The contents of the Data File may be stored as a .TSV file on disk
using the FILE menu and can be imported directly into many common
spreadsheets for subsequent manipulation and analysis. Use the spreadsheet to
perform statistical analysis and produce graphical presentations of the data.
Manufactured by:
Spectrum Techniques, Inc.
106 Union Valley Road
Oak Ridge, TN 37830
USA.
Tel: (865)-482-9937
Fax: (865-483-0473
www.spectrumtechniques.com
[email protected]
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W
R78
U14:C
1N4148
1.00K
GND
.1
3.3M
R75
R77
10K
1K
Q11
8
R71
GND
VDD
WR
CS
DB0
RFB DB1
DB2
OUT1 DB3
OUT2 DB4
DB5
DB6
GND DB7
VREF
GND
13
12
11
10
9
8
7
6
5
4
GND
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
B
2N3904
E
7432
5
R76
4
U10:B
10K
ST 350 COUNTER
Size
GND
Number
A1
TLC7524CN
C29
Date
.1
F
G
Rev
4
G03501
8/16/95
Filename
E
6
Title
DACCS
6
WR*
WP19
C
GND
D
E
+5V
.001
R69A
120K
MPSA13
1
C30
100K
C26
R60
22M
C33
C31
1N4148
+5V
B
1M
WP16
R65
12
14
R73
51K
1
1.00K*
100K
Q10
3K
Q8
D18
R56
1M
C
100
GND
GM TUBE
22M
C
+5V
GND
R58
R59
WP15
B
+
1
1
1N4148
R62
5
4
MC3405P
100
6
D12
R51
D19
A
B
ACTIVITY
2K
1
47K
22M
C24 .01/1000V
U14:A
1
R68
.01
R19
.01/1000V
LM555CHC
C28
C25
D54
C
GND
.1
GND
R53
Q9
R55
3.9K
3
R49
1
3
1M
C20
C22
1M
C25C
1
U15
R57
R48
INSTALL FOR 350W ONLY
XFORMER
VCC
R47
470pF/2000V
R80
8
1N4148
C22A
.01/1000V
WP14
P2
.01/1000V
D22
1
INSTALL FOR 350W ONLY
C21
C34
WP12
1
K
C27
3
+5V
SEGG
U13
GND
1Q
2Q
3Q
4Q
5Q
6Q
7Q
8Q
SEGF
74LS138
U10:A
OC
C
SEGE
DACCS
1
.1
SEGD
ROMCS
3
78C10
SEGC
10
2
U12
SEGB
5
GND
A
6
4
5
7432
C19
5
+5V
GND
GND
A
B
C
R18
10
U7
1
2
3
AB13
AB14
AB15
10
6
1K
47pF
DS1
7
R43
C18
13
12
11
10
9
15
14
a
b
c
d
e
f
g
A
B
C
D
74LS373
8
R42
C
W
DS2
9
1K
47pF
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
BI/ RBO
RBI
LT
7
1
2
6
SA0
SA1
SA2
SA3
10
1K
2.4576
4
5
3
11
R41
7406
C17
BKG
+5V
+5V
12
R39
8
DS3
RTS
13
1K
U6:D
510
510
U4
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
GND
R37
51K
DS4
VPP
PGM
E
G
10
9
8
7
6
5
4
3
25
24
21
23
2
A0
A1
A2
A3
A4
A5
A6
A7
AB8
AB9
AB10
AB11
AB12
GND
1K
GND
1
27
20
22
ROMCS
RD*
R33
510
510
R11
SEGA
GND
C16
10uF
510
R35
E
R10
R16
C14
3
GND
NMI
INT1
RESET
MODE0
MODE1
WR
RD
ALE
PD7
PD6
PD5
PD4
PD3
PD2
PD1
PD0
PF7
PF6
PF5
PF4
PF3
PF2
PF1
PF0
AN7
AN6
AN5
AN4
AN3
AN2
AN1
AN0
12MHz
2
W
PA7
PA6
PA5
PA4
PA3
PA2
PA1
PA0
PB7
PB6
PB5
PB4
PB3
PB2
PB1
PB0
PC7/CO1
PC6/CO0
PC5/CI
PC4/TO
PC3/TI/INT2
PC2/SCK
PC1/RXD
PC0/TXD
STOP
AVREF
AVCC
AVSS
X1
X2
VCC
VSS
510
3
C
C
W
8
7
6
5
4
3
2
1
16
15
14
13
12
11
10
9
24
23
22
21
20
19
18
17
63
42
43
33
31
30
64
32
3
CNT
7406
2
GATE
RES
STP
COUNT
SA3
SA2
SA1
SA0
BKG
CLED
DS6
DS5
DS4
DS3
DS2
DS1
+
-
MODE0
GND
COUNT
U6:A
510
DS5
RESET*
3
SW2
510
E
R9
U8
10uF
2
1
R7
510
E
R8
U11
NMI*
R79
C13
GND
ALARM
E
+5V
R21
2K
7406
1
5
+
R81
2K
1
S1
BUZZER
E
R6
DS6
R17
10K
+5V
1
5
6
B
2N3906
-
2K
4
C2-
B
2N3906
4
Q7
R15
TXD
9
C2+
C11
WP18
T1OUT
B
2N3906
C
Q6
2
R14
2K
3
C1-
WP9
.1
1
B
2N3906
C
Q5
RES
R13
2K
C9
C1+
C
Q4
STP
R12
2K
1
6
B
2N3906
+5V
COUNT
R5
2K
+5V
1
C
Q3
7408
E
2K
TX DATA
C
Q2
2N3906
R4
2
1
7432
I1
BATT
WP5
10K
1
2
7
8
9
10
11
13
14
SEGC
SEGG
SEGB
6
EXT
I5
I6
G
GND
4
MC3405P
S
F12N10L
LBO
3
12
13
D
R1
+5V
11
U2
A
K
Q1
WP2
D3
10uF
U10:D
A
100uH
C1
CHARGER IN
7432
Power Switch
U1
[REV4 08-01-00]
ST350.S01
Drawn by
Sheet
H
1
R.S.S
of
1