overhoff RS400-HTO Manual

OPERATION/MAINTENANCE MANUAL
PORTABLE TRITIUM MONITOR
MODEL RS400-HTO
with Alkaline Battery Option
OVERHOFF TECHNOLOGY CORPORATION
1160 US ROUTE 50, MILFORD, OHIO, USA

SAFETY NOTICE
This Tritium Monitor has been designed and tested in accordance with EN 61010-1. To ensure that
the monitor is used safely, follow all safety and operating instructions in this manual. If the monitor is
not used as described in this manual, the safety features of the monitor might be impaired.
xDo not use the monitor unless it is fully assembled, housed inside the case secured with the
screw fasteners it was supplied with.
xTurn off the power and remove the plug connection from the AC power converter before
removing batteries.
xMake sure the battery covers are properly closed and secured.
xRemove the battery from the monitor if the monitor is to be stored for long periods.
xThis instrument has not been designed for indiscriminate opening or disassembly of the internal
parts. The bias voltage batteries are always connected to the ionization chamber cans, even
when the instrument is switched OFF. The electronics contains highly sensitive
semiconductors which are destroyed by even the slightest electrostatic discharge
xNot suitable for use in wet locations
xNot suitable for use in explosion hazard environments
xRefer to instruction label when connecting to the external jack for supplementary power input.
DO NOT EXCEED 3.5VDC! Use only the AC power converter that was supplied with the
monitor.
SYMBOLS
The following international symbols are used with this manual and equipment:
Important Safety Information in Manual
DC
(
direct current
)

TABLE OF CONTENTS
SECTION PAGE
1.0. INTRODUCTION 1
2.0. TECHNICAL SPECIFICATIONS 2
3.0. CIRCUIT DESCRIPTION 4
4.0. CONFIGURATION 6
5.0. OPERATION 7
6.0. CALIBRATION 10
7.0. MAINTENANCE 12
8.0. SERVICE 13
9.0. WARRANTY 13
10.0. REPLACEABLE PARTS 14
FIGURE 1, FRONT PANEL CONTROLS 15
FIGURE 2, HOSE BARB CONNECTION 16
FIGURE 3, OUTPUT CONNECTIONS 17
DRAWING, J2 OUTPUT CABLE
DRAWING, FUNCTIONAL BLOCK DIAGRAM
DRAWING, GENERAL ARRANGEMENT MODEL RS400-HTO
WITH OPTIONAL ALKALINE BATTERIES
WIRING DIAGRAM, MODEL RS400-HTO
WITH OPTIONAL FOR ALAKINE BATTERIES

Page 1
1.0. INTRODUCTION
The Model RS400-HTO portable tritium monitor is a small, high sensitivity, hand held, battery
operated fully gamma compensated survey meter with an RS232 serial data output. The
instrument case is constructed of light weight aluminum. A handle is attached for hand held survey
use. The instrument will measure tritium in its elemental and oxide form or can be configured to
measure oxide form only.
Note: This special version of the Model RS400-HTO has the Alkaline Battery Option.
1.1. PHYSICAL DESCRIPTION
The Model RS400-HTO uses four identical ionization chambers arranged in a cruciform pattern.
Two ionization chambers, with a total volume of 400 cc, are used for measurement; the other two
chambers serve for gamma compensation.
The sample stream is drawn through the ionization chambers by means of a small rotary vane
pump, which is always plumbed at the outlet of the furthest down stream ionization chamber.
Attaching a good quality particulate filter ahead of the instrument sampling inlet prevents entry of
dust particulates.
A large easy to read liquid crystal digital panel meter with a range from 1 to 19,999 μSv/hr is used
for measurement display.
Other units of measurement, such as MPCa, MBq/m3and μCi/m3or others may be specified by
the user at time of requesting a unit. The instrument exhibits a basic sensitivity of the order of 2
μSv/hr, which it is able to attain due to the fact that it is immune to response to both radon and
cosmic ray noise.
A pair of “D” size batteries supplies power. While it is recommended that Alkaline cells be used,
the instrument will also operate with any type of D-cell batteries, although operating duration
maybe vary. Onset of battery depletion is signaled by illumination of an LED located next to the
meter face. An external power supply can be used by attaching to a small receptacle the side of
the instrument case. The same LED also signals red when the high voltage power supply (HVPS)
used for ionization chamber bias has a malfunction.
DO NOT SUBSTITUTE, use only the recommended external power supply
A ten-position alarm level stepped attenuator, adjustable over partial scale (2 to 1,000 μSv/hr) is
located on the front panel. An OFF position is included. An acoustic signaler emits a steady tone
if the measurement exceeds the set point. An intermittent tone is heard if the sample air flow has
been interrupted. The acoustic alarm is silenced by a “MUTE” push button. The alarms are non-
latching.
External connections for RS232 serial data output has been provided.
For measurements of tritium in the presence of other radioactive gases by means of ionization
chambers appears, at first glance, to be impossible. However, recognizing that tritium oxide is
water, a tritium specific measurement is attained throughtheuse of differentialionization chambers
with an HTO removal dryer interposed between the two ionization chambers. Since all radioactive
components, with the exception of the tritium component is present in both the upstream and
downstream ionization chamber, the net (subtracted) ionization current is now proportional only to
the tritium oxide.
For example: A cartridge filled with disposable desiccant can be interposed between the
measurement and compensation ionization chambers will yield a net measurement response only
to tritium oxide; HTO + other nuclide - (other nuclide) = HTO
Gas flow connections are made externally to the instrument by appropriate attachment of flexible
plastic hose. See Figure 2.

Page 2
2.0. TECHNICAL SPECIFICATIONS, MODEL RS400-HTO
MEASUREMENT DISPLAY 4 1/2 digit LCD
MEASUREMENT RANGE 1 to 19,999 μSv/hr
NOTE: Conversion factor according to ICRP-68 Table C1
where: 1 μSv/h = 3.09E4 Bq/m3= 0.835 μCi/m3
SENSITIVITY 2-3 μSv/hr h (2 μCi/m3)
ACCURACY ±10%
GAMMA COMPENSATION multiple chambers in a cruciform pattern to reduce errors due
to external gamma radiation Gamma response less than 0.2
μSv/hr per mR/hr for any field direction.
RESPONSE RATE 30 seconds to reach 90% of final reading,
NOISE LEVEL ± 2 μSv/hr 1 S.D. (10 second electronic time constant)
ZERO STABILITY ±2 μSv/hr after 3 minutes (or less) warm-up
ALARM (ACOUSTIC) 1. ten position stepped attenuator set point for signal alarm
2 to 1,000 μSv/hr, steady tone. OFF position included.
2. low flow produces an intermittent tone
3. Mute switch silences audible tone
ALARM (VISUAL) LEVEL: red LED; when tritium level exceeds set point
FLOW: yellow flashing LED; low pump flow
LOW BAT: red LED; D-cell batteries need to be replaced
-AND-
HVPS: red LED illuminates to indicate a malfunction
with the high voltage power supply (HVPS)
used to bias the ionization chambers
EXTERNAL CONNECTIONS miniature DIN plug with RS232 serial data output for tritium
measurement, and alarm status
DUST FILTERS in line disposable cartridge, Pall P/N 12082
SAMPLING SYSTEM 6 hose barb ports are located on the
front panel
PUMP miniature internal pump for 3 to 5 volume changes per minute

Page 3
TECHNICAL SPECIFICATIONS, MODEL RS400-HTO, continued
IONIZATION effective volume: 400 cm3
CHAMBER VOLUME port to port volume: 440 cm3
POWER Alkaline Battery Option
Requires two “D” size batteries Alkaline type with
external jack for supplementary power input
ENVIRONMENTAL 0°C to +40°C
20 to 90 % R.H. Non-Condensing
CASE light weight aluminum
SIZE AND WEIGHT 7.6" L, 5.2" W, 6.9" H excluding handle,
6.5 lbs (3 kg)
ACCESSORIES
•2 “D” size batteries, Alkaline type, removed from battery
compartments during shipment
•Sniffer hose
•Dust filter
•2.3 meter long cable for RS232 serial data. Mini-DIN plug
for J2 output connector at one end with DB9 plug for serial
connection on other end
•Power converter
100-240 VAC, 50/60 Hz, .25 A to 3.3 Vdc @ 1.2 A
5.5 mm O.D. x 2.1 mm I.D. Plug
Center pin is positive
DO NOT SUBSTITUTE, use only the recommended
power supply
ADDITIONAL ACCESSORY ITEMS FOR RS400–HTO VERSION:
•2 each, desiccant column for HT-HTO measurement;
while one is being used the other may be regenerated
•1 each, dust filter P/N 12082, a second dust filter for the
inlet to the downstream chambers when using the
desiccant
•2 each, mounting clips for desiccant column, location to
suit customer
•Additional sniffer hose and fittings for making all hose
connections to the desiccant columns

Page 4
3.0. CIRCUIT DESCRIPTION
3.1. IONIZATION CHAMBERS
In its simplest form, an ionization chamber is an enclosed volume with two electrodes. Voltage is
applied between the electrodes, generating an electric field, which will segregate and collect
electric charges, which are created by nuclear events occurring inside the chambers. Nuclear
events may consist of ionization of air molecules by external or internal alpha, beta or gamma
radiation.
The RS400 monitors are designed to measure tritium. Activity of tritium decay is such that a
concentration of 1 μCi/m
3
in a volume of one liter will generate an ionization current of about 0.95
x 10
-15
amperes. This is a very weak current.
Alpha pulses from naturally occurring radon, are much more energetic, they can produce short
current bursts of up to 10
-13
coulombs during decay, and therefore appear as large noise "spikes"
which can seriously impair tritium measurement.
Gamma radiation also has a strong effect. In practice, a gamma radiation field of 1 mR/hr will
create the same amount of ionization as 90 μCi/m
3
of tritium.
A tritium monitor, in order to measure to low concentrations, must be able to respond only to tritium
and be immune to alpha or gamma radiation. For this purpose, a second ionization chamber
system has been included to balance out any ionization current contribution from external gamma
radiation.
In theRS400 instruments,the four ionizationchambersare arrayedin a cruciformpattern, ensuring
almost perfect gamma compensation in all directions and evenfor high gradient non-uniform fields.
The ionization chamber polarizing voltage is supplied by an electronic high voltage power supply.
The surfaces of the ionization chambers have a thin coat of paint for insulation, but it is best to
avoid touching them.
3.2. ELECTROMETER
Also knownas atransimpedanceamplifier, it serves the purpose of converting the extremely feeble
ionization current into a voltage suitable for further signal processing and measurement display.
The heart of the electrometer consists of a specially selected dual ultra high impedance
semiconductor device which has been chosen both for ultra low internal current leakage as well
as long term d.c. stability. The semiconductors used in the RS400 instruments are suitable for
measurement of currents as low as10
-16
amperes.
In the RS400 instruments, the electrometer is directly attached to the ionization chamber cluster
and is protected by a rectangular metal cover.
CAUTION: This instrument has not been designed for indiscriminate opening or
disassembly of the internal parts. Electrostatic charge from the bias voltage on the
ionization chamber cans will be present even when the instrument is switched OFF.
The detector pre-amp contains highly sensitive semiconductors which are destroyed
b
y
even the sli
g
htest electrostatic dischar
g
e.

Page 5
3.3. SIGNAL PROCESSING AMPLIFIER
A single printed circuit board attached directly to the front face of the instrument contains all power
supply and signal processing electronics.
Proprietary circuitry is used for the recognition and elimination of transient signals due to radon or
high-energy cosmic ray pulses. The RS400 instruments, with digital display, use a dedicated
internal circuit to disable the pulse rejection circuit when the measured signal reaches
approximately 80-100 μSv/hr.
An OFFSET control is furnished in order to adjust the reading to zero in case of offsets caused by
tritium contamination of the chambers or otherwise.
A front panel control has been provided for adjustment of the set point (level) at which the acoustic
alarm is desired to sound. The acoustic signaler has the second function of alerting the user that
sample gas flow is impeded.
All power supplies are regulated. A warning LED on the front panel will illuminate red when the
battery terminal voltage has dropped to about 2.2 V. This signals that the batteries should be
replaced – WITHIN 1 HOUR AFTER THE WARNING LED ILLUMINATES. It will also illuminate
when the high voltage power supply (HVPS) operates outside of specified voltage range.
Two plug and jack connections are found on the sides of the instrument. One is for an external
power, and the other is the RS-232 cable connection to a personal computer.

Page 6
4.0. CONFIGURATION
4.1. EXTERNAL FEATURES
The front panel features include:
1. the digital panel meter, 1 to 19,999 μSv/hr
2. function control knob
3. alarm level control knob, 2 to 1,000 μSv/hr
4. red LED; dual function; low battery, indicates when the D-cell batteries need to be
replaced and indicates red if the high voltage power supply (HVPS) has a malfunction
5. signal level alarm LED
6. low flow alarm LED
7. acoustic signaler
8. mute push-button
9. calibration potentiometer (under phillips head screw)
10. offset potentiometer (small knob)
11. six sample hose barbs
12. two D-cell battery compartments
Side features include:
13. jack for external charger, 3 to 3.3Vdc, 1.2A-3A, DO NOT SUBSTITUTE, use only the
recommended power supply
14. 8-pin mini-din receptacle for RS232
15. GAMMA CHECK label for position of check source, refer to section 6.0.
16. snap holder for dust filter
4.2. HOSE CONNECTIONS
The instrument may be operated in either of two modes. In the first mode, the instrument will
respond to any radioactive gas passing through the instrument as well as tritium. In the second
mode, it will respond only to HTO, even in the presence of other radioactive gases. The external
plumbing (hose attachments) is selected to suit the mode in use.
FIRST MODE (refer to Figure 2) Measures total tritium plus any noble gases when present
A sniffer hose is attached to a small in line dust filter, which is directly attached to the “IN” hose
barb. The other measurement chamber hose barb is routed to the inlet of the pump by means of
a short piece of hose. Connecting a short loop of hose to each hose barb closes off the
compensation chambers hose connections.
SECOND MODE (refer to Figure 2) Measures HTO only with noble gas compensation
In this mode, the exhaust from the measurement chambers is connected to a desiccant cartridge.
The exhaust end of the desiccant cartridge is connected to a second dust filter and then to the inlet
of the compensation chamber. The other compensation chamber hose barb is routed to the inlet
of the pump by means of a short piece of hose. Inthis mode, thesamplestreampassesfirstthrough
the measuring (upstream) chambers, and then through the desiccant cartridge, it continues through
the compensation (downstream) chambers and finally exits via the pump.
Note 1: Never Operate The Instrument Without A Dust Filter In The Sample Stream
Note 2: The Instrument Must Be In Thermal Equilibrium With Its Surroundings.
Note 3: To Avoid Erratic Response, The Pump Must Always Be Placed Downstream Of
The Last Ionization Chamber In The Sample Path.

Page 7
5.0. OPERATION
Ensure that a dust filter is connected in line ahead of this instrument flow inlet in use. The following
steps are necessary and sufficient to operate the instrument:
1. Set measurement alarm level to desired value.
2. Rotate mode switch to “MEASURE”. The “low flow” LED will flash, since the pump is inactive.
The “mute” switch will silence the intermittent tone if desired.
Allow 30 seconds for the instrument to be ready to sample. Allow an additional two to three
minutes for the instrument to stabilize. Readjust (if necessary) by turning OFFSET control knob
to achieve a zero reading on the meter
NOTE: The rotation direction for the adjustment is clockwise for change in a positive
direction. Use very small amounts of rotation, the display will not react
immediately because there is a 30 second time constant.
The instrument is now ready for use. In this mode the ionization chambers are active, but the pump
is not. The instrument is in a so-called “standby mode” ready to sample the instant the mode
switch is advanced to the next position.
3. Rotate the mode switch to the sample position. Now, the pump is operating and the low flow
indication will be eliminated.
If it is desired to operate the instrument continuously on an external power supply, only a source
of 3.3VDC, 1.2-3A current capacity should be used. Attaching the external power plug will
automatically disconnect the D-cell batteries.
NOTE: If the audible alarm is an intermittent tone, sample flow through the chambers is
below specification. This could be an obstructed sampling hose or other
It is IMPERATIVE that the sample stream be free from dust, dirt or moisture. Not only will the
instrument show erratic behavior, but also it may cease to function entirely. If moisture is ingested,
then continued pumping to evaporate and expel the moisture can be attempted. If this fails, the
instrument must be returned to the factory for service.
Condensation can occur if an instrument is brought from a cold environment into warmer
surroundings.
Furthermore, temperature changes to the instrument, both lower to higher as well as higher to
lower will create transient currents in the electrometer which can appear as large phantom
measurement signals.
The instrument must be allowed to thermally equilibrate to its surroundings prior to use. When
there is an OFFSET due to thermal disequilibrium, use the following procedure:

Page 8
OFFSET COMPENSATION:
1. Switch the instrument into the measure model.
2. After approximately three minutes. The instrument should indicate 0000 on the digital panel
meter. An offset of 5-7 μSv/hr is typical for situations due to temperature changes. This offset
should disappear as thermal equilibrium is attained.
3. Adjust the “offset” compensation potentiometer as required. The location is shown in Figure 1.
NOTE: The rotation direction for the adjustment is clockwise for change in a
positive direction. Use very small amounts of rotation, the display will not
react immediately because there is a 30 second time constant.
GENERAL OPERATION NOTES:
The following information is provided to the user to ensure stable and accurate performance.
The monitor can be located on any flat surface, such as a table top, or, it can be mounted to a wall
bracket or shelf, or on a small moveable cart. In all cases, the instrument must be protected
against vibration, shock, moisture and dirt.
ELECTRICAL GROUNDING
The electrical and electronic equipment grounding is often considered only from the viewpoint of
hazard and safety. Indiscriminate or excessive grounding may actually enhance the potential of
danger and disturb the proper internal operation of the instrument. The electronic circuitry,
including logic, adjustment controls, local and remote displays, are centrally and all inclusively
grounded at the ionization chamber module. The circuit system common line is electrically
connected to the metal frame or housing of the electrometer module. When signal outputs are
connected to remote displays, computer interfaces, or similar devices, it is necessary that no
significant ground potential differences exist between the monitor and other equipment. If
significant potential ac or dc differences exist, shifts in the instrument “zero” can appear.
THE FOLLOWING IS RECOMMENDED
1. Make all interconnections. Normally the instrument operates on (2) “D” cell batteries. If it is
desired, the instrument can operate continuously by connecting to the AC power converter
provided. Use only the AC converter that is provided. Activate the instrument. Allow ten
minutes “warm-up”. Adjust zero if needed.
2. Attach remote connections (devices) and verify absence of change in zero.
If zero has changed, check for ground loops and spurious ac or dc potential differences from one
location to the other.
NOT SUITABLE FOR USE IN WET LOCATIONS
NOT SUITABLE FOR USE IN EXPLOSION HAZARD ENVIRONMENTS

Page 9
RS232 OUTPUT
The RS232 interface serves the purpose of transmitting data to any digital computer via a standard
2 wire RS232 link.
The data includes:
The tritium measurement level, status for level and flow alarms, alphanumeric information
representing location and identification for the instrument.
With a personal computer use Hyper Terminal or another suitable application to view the data.
The COM Port setting should be 9600 baud, 1 start bit, 8 data bits, parity = none, 1 stop bit, and
flow control = none. The tritium monitor is capable of transmitting data only. The data is illustrated
below. There are eight fields with single spaces between the fields. The data string is terminated
with “\r\n”.
The data string appears as shown below followed by an explanation of each field.
:A0F1 000421 uSv/h.. 004199 L0H0 0090 1.10 00000523
Field 1 (A0F1):
: = start character
A = “Alarm” (high tritium alarm)
0 (no alarm) or 1 (alarm)
F = “Flow Alarm”
0 (flow is OK) or 1 (low flow – blocked filter, bad pump, or blockage)
Field 2 (000421): Tritium value
Field 3 (uSv/h..): Tritium unit of measure
Field 4 (004199): Serial number of instrument
Field 5 (L0H0): L = “Low voltage power supply alarm”
0 (voltage is OK) or 1 (voltage is low)
H = “High voltage power supply alarm”
0 (voltage is OK) or 1 (voltage is low)
Field 6 (0090): Approximate percentage of battery remaining (90%)
Field 7 (1.10): Microcode version
Field 8 (00000523): Sequence number

Page 10
6.0. CALIBRATION
6.1. METHOD
Tritium monitors employing ionization chambers, such as the 400 series portable instruments may
be calibrated with either of two methods.
The first method consists of injecting a known activity of tritium gas; the second method uses
external gamma radiation of known field strength.
To ensure traceability to National Standards, the first method must be employed. This method is
time consuming, and is quite difficult to perform with precision. This first method is, however,
useful as a “type” test, and can serve as a basic accurate calibration from which the gamma
response (the second method) can be cross-correlated.
The second method uses an external gamma field. In this instance, the polarization of the
compensation ionization chambers is reversed to coincide with that of the measurement ionization
chambers.
In this condition, the effect of externalgamma radiation now adds rather then cancels, and a known
gamma field should produce a predetermined measurement indication.
6.2. GAS CALIBRATION
Since the instrument is essentially linear, a relatively high concentration can be used for most
accurate results. Values between 100 – 1,000 μSv/hr are convenient, but any other values from
20 – 5,000 μSv/hr can be used.
Themanufacturer ofthe gas calibrator generallyprovides instructions forthe use ofgas calibrators,
and these should be followed.
Some general hints can be given.
It is important that the calibration sample be well circulated through the entire calibration system
loop.
Adequate time should be allowed for the system pressure and temperature to come to
equilibrium, and that no excess pressure is built up.
The inclusion of a previously calibrated "master" or "reference" tritium monitor in the sampling loop
is highly recommended.
The calibration can actually be repeated for several levels of tritium activity. This is not done to
verify the linearity of the tritium monitor (which is highly linear) but to ensure that the calibration
process itself is free from subtle errors.

Page 11
6.3. GAMMA CALIBRATION
If the unit has previously been calibrated with tritium gas, then it is sufficient to use a gamma
radiation source to produce a response when placed at a specified location relative to the
instrument under test. Lead shielding is advised since the compensation chambers will cancel the
measurement. It is best to shield both of the compensation chambers plus one of the
measurement chambers. Use a minimum of ½” thick lead. For the highest value response, the
gamma source should be directed through the bottom of the case to minimize interaction with the
compensation chambers. If the gamma source is long lived, no chronological correction is needed.
To verify calibration at a future date, the original gamma source must be used. Records must be
kept to identify relative location of the source and the expected result. Be sure that temperature
and pressure variations are taken into account.
If calibration by either of these methods is performed, and the instrument response is somewhat
different from the expected value, then small adjustments can be made by turning the calibration
potentiometer with a small screwdriver. The calibration potentiometer is accessed by removing
the small Phillips head screw on the front panel located above the label CAL.
Large changes in calibration are evidence of malfunction. The factory should be consulted
immediately.
OVERHOFF TECHNOLOGY CORPORATION
Telephone [phone]
Facsimile [phone]
Email: [email protected]
6.4. GAMMA CHECK
If a tritium monitor has previously been calibrated by any other method, gas or gamma, a low
intensity gamma radiation source check can be used as a quick verification of monitor
performance. On the left side of the instrument case towards the front which is the defined location
for “GAMMA CHECK”. When using the identical gamma check source, at the defined spot, it
should always produce the same instrument response, provided, of course, temperature and
pressure variations are taken into account. This source check may be performed at a frequency
of your choice, it could be daily, weekly or monthly. We recommend a low intensity gamma check
source of the type which is commonly intended for G-M counters or other survey instruments. For
example; a 10 micro Curie, Cesium-137 check source should be sufficient for a monitor reading of
100-200 μSv/hr.
IMPORTANT: Do not adjust the calibration when performing a gamma check.

Page 12
7.0. MAINTENANCE
Overhoff 400 series portable instruments have been designed for many years of trouble free
service. Very little maintenance is required, but some periodic attention may be necessary,
especially if the instrument is to be used in adverse environments.
Pump life is in excess of 1000 hours of actual use; ensuring that the instrument is operated only
with dust filters in line preserves its life.
When not in use, the monitor should be stored in a cool dry environment.
OPERATOR MAINTENANCE
The following operational checks may be performed at daily, weekly or monthly intervals to suit.
Inspect dust filter for excessive dust build up. Check the flow rate. Does the pump have sufficient
flow such that the Low Flow Alarm is not indicated when 10ft of the sniffer hose is connected to
the inlet of the dust filter?
GAMMA CHECK, If a tritium monitor has previously been calibrated by any other method, gas or
gamma, a low intensity gamma radiation source check can be used as a quick verification of
monitor performance. On the side of the instrument case towards the front which is the defined
location for “GAMMA CHECK”. When using the identical gamma check source, at the defined
spot, it should always produce the same instrument response, provided, of course, temperature
and pressure variations are taken into account. This source check may be performed at a
frequency of your choice, it could be daily, weekly or monthly. We recommend a low intensity
gamma check source of the type which is commonly intended for G-M counters or other survey
instruments. For example; a 10 micro Curie, Cesium-137 check source should be sufficient for a
monitor reading of 100-200 μSv/hr.
IMPORTANT: Do not adjust the calibration when performing a gamma check.
Manipulate the alarm set point to verify correct functioning of the alarm.
If the instrument is suspected of DRIFT, the zero reading may be verified. This should be done by
an instrument engineer or technician.
SUPERVISORY MAINTENANCE
The following tasks are the responsibility of the supervisory engineering staff.
1. Calibration verification is to be performed at yearly intervals, or as otherwise specified.
2. Response checks (in case of need for cursory verification of the operational status of the
ionization chambers and of the whole system), of the system may be tested by using a low
strength gamma radiation check source. This must be done under the strict supervision of a
health physicist. The gamma source is brought into proximity of each ionization chamber and
the response is observed.
FACTORY MAINTENANCE
A determination that the system appears to have suffered a functional failure should require that
the factory be notified (telephone [phone], facsimile [phone]). Engineering
assistance via telephone or facsimile, will be supplied by the manufacturer OVERHOFF
TECHNOLOGY CORPORATION.
Should it appear to be necessary to return the instrument to our factory, authorization for the return
must be obtained from Overhoff Technology Corporation prior to shipping. In-freight charges will
be borne by the customer.

Page 13
7.1. D-CELL BATTERY REPLACEMENT
The Model RS400-HTO with optional Alkaline batteries uses (2) “D” size Alkaline batteries. The
batteries will need to be replaced within an hour after the low battery light illuminates.
NOTE: Remove the batteries before shipment or inactive storage of more than 30 days
This instrument contains components that are easily destroyed if the case is opened and
handled without proper precaution. If damage occurs, the repair will not be covered under
warranty. Avoid touching the ionization chambers and the PC Board Assemblies to reduce
the risk of damage.
8.0. SERVICE AND SUPPORT
This instrument contains highly sensitive semiconductors which are destroyed by even the
slightest electrostatic discharge if the case is opened and the instrument is handled without proper
precaution.
Special training can be given to qualified technical personnel who are entrusted with instrument
service and repair responsibility.
Warranty is void if maintenance or repair (other than that which is listed in this manual) is
performed by an unauthorized repair facility.
OVERHOFF TECHNOLOGY CORPORATION
Telephone [phone]
Facsimile [phone]
Email: [email protected]
9.0. WARRANTY
All instruments built by Overhoff Technology Corporation are warranted to perform as claimed.
Defective components or workmanship of the instrument will be corrected free of charge for parts
or labor within a period of one year from delivery. Nonperformance of the instrument as a result of
negligence on behalf of the customer is not covered by this warranty.
Should it appear to be necessary to return the instrument to our factory, authorization for the
return must be obtained from Overhoff Technology Corporation prior to shipping. In-freight
charges will be borne by the customer.

Page 14
10.0. REPLACEABLE PARTS
The following parts and components are disposable items and may be obtained from Overhoff
Technology Corporation or from any original supplier:
Battery, "D” size, alkaline P/N EN95,(qty 2 req’d)
Dust Filter P/N 12082
Ionization Chamber Can P/N 1020686
Pump P/N 50084
Hose Barb, Sample Inlet Brass, P/N 22BH-4-2
Hose Barb, Sample Outlet Brass, P/N 230-4-2
Panel Meter P/N DMO-742W
AC power converter P/N KTPS05-03315U-VI-P1
Input: 100-240 VAC, 47-63Hz, 0.25A
Output: 3.3 Vdc @ 1.2A,
Output Plug: 5.5 mm O.D. x 2.1 mm I.D. Plug Center pin is positive
DO NOT SUBSTITUTE, use only the recommended power supply
Fuse, 2 Ampere P/N MDL-2
RS232 Cable P/N J2-RS400-2M (2.3 meter length cable is standard, a maximum
length of 15 meters is available)
Desiccant Cartridge Drierite P/N 26800
Mounting Clips for above Drierite P/N 26809
Replacement Desiccant Drierite P/N 23005 ( 5 lb jar)