Range: 1 to 19,999 µCi/m3
Useful as a room or stack monitor
The Model 357RM is a low-cost, general purpose stationary tritium air monitor, designed for continuous duty. The 357RM tritium monitor has been a work-horse for over 30 years. The system has proven to be user-friendly, accurate, and reliable. It is ideal for measuring airborne tritium concentration in rooms, stacks, exhausts, glove boxes, and similar environments.
The 357RM includes the essential components required for the accurate measurement of tritium in air: dual 2 L ionization chambers with coaxial gamma compensation, long life pump with HEPA filter (99.99% efficiency at 0.1 micron) and flowmeter, alpha pulse suppression, and a single adjustable alarm set-point with audible and visible alarm. The HEPA filter component is located on the front panel for easy inspection and service. The unit is suitable for 48 cm rack-mount or table-top use.
- Continuous Duty Tritium Air Monitor
- Coaxial gamma compensation (2L volume) with virtually no offset in fields up to 20 mR/h and built-in ion-trap
- Sensitivity: 1 µCi/m3, 1 MPCa, or 0.04 MBq/m 3
- Range: 1 to 19,999 µCi/m3 , 0.1 to 1,999.9 MBq/m 3\, DAC, and MPCa, 0.01 to 199.99 MBq/m3
- Single adjustable alarm set-point
- Audible and visual alarm indicators for signal level, low flow (optional)
- Alpha pulse suppression, radon rejection
- Long-term zero stable, span calibration is permanently stable due to special electrometer design
357RM Options:
- Low flow alarm with alarm indicator on the front panel and relay contacts on the rear panel
- Plate-out proof wire grid ion chambers to reduce tritium/gamma contamination by up to 1000x
- HTO only measurement and noble gas compensation
- Choice of one additional data output: RS-232, 4-20mA, or Ethernet
- Remote display unit
- Mounted on wheeled stainless-steel cart for portability
The Model 357RM includes a standard 0-10 VDC analog output found on all our stationary instruments and can support one additional data output (choice of: RS-232, RS-485, 4-20mA, or Ethernet). It has a simple alarm system consisting of a single independent signal alarm and a toggle switch with three alarm modes: on, off, and reset. The signal alarm activates the acoustic signal and will continue to operate until manually reset, even if the displayed signal has receded below the setpoint. A remote alarm unit can be added that includes a latching or timing circuit to easily mute and re-set the alarm. Relay interface connections are included on a terminal block at the rear of the enclosure. An optional low flow alarm with a front panel alarm indicator can also be added.
Proprietary circuitry provides recognition and cancellation of undesirable noise spikes attributed to airborne radon. Unique plate-out proof wire-grid ion chambers are available in place of the standard solid-wall chambers which will reduce tritium contamination by three orders of magnitude by decreasing the true surface area of the chamber.
If requested, the HTO gas ports can be installed on the compensation chamber for noble gas or other radioactive gas compensation.
The only maintenance required for the 357RM is periodic service of the pump and replacement of the dust filter. The sensitivity, accuracy, and noise level of the Model 357RM is superior to competitive instrumentation by an order of magnitude.
Calibration of the 357RM tritium monitor can be accomplished by three different methods:
- Tritium gas calibration: Injecting tritium gas into the ionization chambers to produce an accurately predictable concentration and adjusting the calibration potentiometer accordingly. Overhoff offers factory calibration services and also provides tritium gas calibrators for the customer to calibrate on-site.
- Gamma calibration using a gamma source: Using a certified gamma range or source, tritium monitors can be calibrated using the relationship that 1mR/hr yields the same ionization current as 90 µCi/m 3 of tritium.
- Electrical equivalence method: All Overhoff ionization chamber – electrometer modules carry a BNC receptacle to which a precisely calibrated ultra-high resistor can be attached. Using Ohm’s law and knowing the volume of the ion chamber, you can calculate the current value and expected panel meter display and adjust the calibration potentiometer as required. Calibration resistors are available for purchase.
Range
Available in the following ranges:
a) 1 to 19,999 μCi/m3, MDA is 1 μCi/m3
b) 0.01 to 199.99 MBq/m3, MDA is 0.04 MBq/m3
c) 0.1 to 1,999.9 DAC where 1 DAC=10μCi/m3
d) 1 to 19,999 μSv/h, MDA is 1 μSv/h
Extra-sensitive option: e) 0.1 to 1,999.9 μCi/m3 , MDA is 1 μCi/m3
Display
Digital Meter, 4 ½” digit LED
Accuracy
±10 % of reading, ±1 μCi/m3, whichever is greater
Stability and Drift, Long Term
±1 μCi/m3, ambient temperature
Noise
±1 μCi/m3, 2 sigma, with 20 second time constant
Gamma Compensation
second ionization chamber of equal volume, coaxially mounted, serves to cancel effects of external gamma fields
Response Rate
Two linear time constants
20 seconds for measurements below 80 μCi/m3
3 seconds for measurements above 80 μCi/m3
Alarm System
single alarm, with set point adjustable from 1 to 1,000 μCi/m3
Indicator
acoustic signaler, red LED
Ionization Chamber Volume
measuring: 1,600 cm3
total wetted: 2,000 cm3
Ion Trap
Kanne Type, coaxial integral
Ports
hose barb fittings for 3/16″ I.D. vinyl tubing
Flowmeter
0-10 LPM adjustable rotameter
Dust Filter and Pump
high efficiency respirator type cartridge.
long life continuous duty oscillating piston positive displacement pump
Environmental
storage: -40° C to +60° C
Operating: 0° C to +50° C
0 to 95 % R.H. non-condensing
Power
115 VAC or 240VAC, 50/60 HzPHYSICAL CABINET19 “ rack mount, aluminum sheet metal
Dimensions
8.8 in [223mm] H x 19.0 in [483mm] W x 6.0 in [406mm] D
Weight
40 lbs. [18.2Kg]
Options
-Plate-out proof wire-grid chamber to reduce tritium contamination
-For HTO only measurement: Gas ports for noble gas compensation
-Low flow alarm
–Choice of one data output:
RS232, USB, Ethernet, 4-20mA, or logarithmic output
