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965 Stack Radiation Monitoring System

 965 Stack Continuous Air Radiation Monitoring System

965 Stack Radiation Monitoring System

The Model 965 Stack Monitor is a single-channel radiation monitoring system capable of operating over the range of 10 to 107 CPM. The system monitors gamma radiation and provides indication when the radiation level decreases below a fail threshold, exceeds a warn set point, exceeds a high set point, or exceeds an overrange set point. The overrange feature provides two significant benefits. First, it prevents the system from displaying an on-scale, but inaccurate, reading should the detector become saturated. Second, it lessens the risk of damaging the detector by disabling it during an overrange condition. Relay outputs are available to activate alarm annunciators. Analog outputs are available for trend display on a strip chart recorder or computer. In addition, the monitoring system has an integral check source to verify operational integrity.

The system consists of a Model 943-36CS Gamma Scintillation Detector and a Model 942A Universal Digital Ratemeter (UDR).


  • Gamma Scintillation Detector with built-in radioactive check source
  • Monitors radioactivity in exhaust stacks or ducts, and in positron emission tomography (PET) applications
  • Airborne 15O monitor
  • For use with Model 942A UDR or Model 960 electronics
  • Stack/duct flow monitoring capability
Key Features

  • Count Range: 107 CPM
  • Energy response: 15% from 70 keV to 3 MeV
  • No external power needed at detector location
  • Preamplifier integral with detector
  • Ratemeter may be remotely located up to 1500 feet
  • Single cable between ratemeter and detector
  • 8 µCi 36Cl check source
  • Replaces high maintenance off-line monitoring system
  • Deadtime correction < 1% at 107 CPM
  • User adjustable alarm setpoints
  • Seismically tested with high reliability
  • Stack flow monitoring and release calculation
  • Specifications, Gamma Detector


The 965 Stack Monitoring system is designed to be used in any size or shaped stack. Since the detectors are mounted directly in the stack, there is no need for an expensive or high maintenance off-line monitoring system. This monitor can be used as a single channel, stand-alone, or grouped together as a multi-channel monitoring system.

The standard UDR is factory-modified to include three option boards to allow for computer communications, an analyzer to count 15O (or other selected isotopes) only, and flow compensation to measure stack effluent releases.

Specifications, Gamma Detector

The Model 943-36CS Gamma Scintillation Detector consists of a scintillation crystal, a photomultiplier tube, a preamplifier assembly and an integral check source.

The Model 943-36CS detector is designed to be sensitive to gamma radiation. The scintillation material, photomultiplier tube and preamplifier are contained within a cylindrical housing.

The preamplifier provides pulse conditioning and cable driving capabilities to match the input characteristics of the instruments used to monitor the detector output.

The Model 943-36CS Gamma Scintillation Detector can be used with Universal Digital Ratemeters or with the 960 Digital Radiation Monitoring System (DRMS). Ratemeters are used in systems where individual control room readouts are employed, while the 960 DRMS is used when a complete digital process control system is supplied.

Specifications, Universal Digital Ratemeter
The Model 942A UDR, when connected to a Model 943 Series Scintillation Detector, comprises a monitoring system which operates over a seven decade range. The UDR provides display, control, and annunciation functions for the monitoring system, and will display readings in the range of 10 to 107 CPM.

Standard features for the instrument consist of a five digit display of the radiation value and a multicolored bargraph indicator which covers the entire range of the UDR. The bargraph will change color in the event of an alarm condition (green for normal, amber for warning and red for high). Front panel alarm indicators and rear panel relay outputs for alarm annunciation are also included. Front panel pushbuttons are provided to apply power, display alarm limit set points, acknowledge alarms, and activate the check source.

Analog outputs of 0 to 10 VDC (1) and 4 to 20 mA (2) are provided for recording and computer monitoring. The outputs may also be used to drive a remote meter or a local (i.e. near the detector) indicator.

All electronics required to interface with a Model 943 Series detector are included within the Model 942A UDR. The electronics consist of a high voltage power supply, low voltage DC power supply and the hardware/software required for UDR operation. The system also includes an overrange indicator to preclude the possibility of on-scale readings when the radiation field is beyond the range of the detector.

 2.5 in Ø x 16 in long (63.5 x 406.4 mm)
 5 lb (2.27 kg)
Housing material
 Stainless steel
Check source housing
 PVC plastic
Operating temperature:  32º to 122ºF (0º to 50ºC)
Storage temperature:  32º to 122ºF (0º to 50ºC)
Relative humidity:  0 to 95% non-condensing
End window material
 Stainless steel
Crystal characteristics
Material:  NaI (Tl)
Full width half max:  < 9%
Configuration:  1.5 x 1 in
Energy response range:  70 keV to 3 MeV
Electrical characteristics
Photomultiplier tube:  2 inch Ø, 10-stage, integral crystal
Maximum count rate:  107 CPM
Output pulse polarity:  Negative
Output impedance:  50 ohms
Rise time:  < 60 ns (preamp alone)
Maximum field cable length:  1500 ft (457 m)
Maximum pulse amplitude:  - 6 V (terminated into 50 ohms)
Connector type:  MHV high voltage
Power requirements  Detector: 1400 VDC max @ 500 µA
Preamplifier: ± 15 VDC @ 50 mA

Specifications (Universal Digital Ratemeter)
Main display
 5 digits with backlighted radiation units display and floating decimal point. 3 digits plus exponent for data entry/display
Bargraph display (dynamic range)
 3 segments per decade, tricolor, indicating channel status. 10 to 107 CPM
Alarm indicators
 HIGH (red LED), WARN (amber LED), FAIL (red LED) and RANGE (red LED)
Setpoints:  HIGH-High Alarm limit, WARN-Warn Alarm limit
Check source:  Activates check source and associated green LED indicator. Momentary non-latching pushbutton operation
Alarm acknowledgement:  Alarm acknowledgment causes alarm indicators to go to a steady on state after acknowledgment
Power ON/OFF:  Alternate action pushbutton for AC power to unit
Relay outputs (fail-safe operation)
High alarm:  1 set. DPDT rated 5 A @ 120 VAC (one set 120 VAC powered for use with optional remote alarm)
Warn alarm:  2 sets. DPDT rated 5 A @ 120 VAC
Fail alarm:  2 sets. DPDT rated 5 A @ 120 VAC; Contact rating for all relays is 5 A @ 28 VDC
High-voltage output
 1400 VDC max @ 0.5 mA
Check source power
 ± 15 VDC @ 20 mA
Analog outputs
 4 to 20 mA (2) (500 ohms max) and 0 to 10 VDC (1 k-ohm min), logarithmic. May be scaled for any one decade (min) to the full range of the unit (max)
Alarm acknowledgement input
 Optically isolated DC input
Detector input
 Digital pulse, up to 1500 feet from UDR, 50 ohm input impedance
Detector accuracy (electronic)
 ± 1% digit (± 1% of the displayed value), exclusive of the detector energy response
 5.64 (w) x 13.73 (d) x 3.47 in (h); (14.33 x 34.87 x 8.81 cm)
 4 lb (1.8 kg)
 120 VAC ± 10%, 50/60 Hz, 28 W
Heat loading
 Approximately 96 BTU/hr
Operating temperature:  32° to 122°F (0° to 50°C)
Storage temperature:  32° to 122°F (0° to 50°C)
Relative humidity:  0 to 95%, non-condensing
 Model 948-1 Rack Chassis, designed to mount 3 UDRs in a 19 inch wide cabinet
Model NameDescription
965Stack Monitor

Miscellaneous Accessories
948-1Rack Chassis (part# 948-1)

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