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Model 940-1 Off-Line Gaseous Effluent Monitor

Off-Line Gaseous Effluent Monitor

Model 940-1

Victoreen 940-1 Particulate, Iodine, & Noble Gas Monitoring Systems are collaboratively configured with our customers in order to meet required specifications. The collaborative nature of our engineering team ensures that layout, sensitivity, seismic, regulatory, or other difficult requirements are adhered to in order to solve our customer's problems.

Data Sheet

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Key Features

  • Universal Digital Ratemeter with dynamic range up to 107 CPM
  • Scintillation type detectors
  • Optimized sampling geometry for maximum sensitivity
  • Rugged open frame skid construction for ease of maintenance
  • Positive displacement type pumping system
  • Automatic pressure compensation for gas density
  • Class 1E qualification available


The Code of Federal Regulations requires assurance that radioactive materials within airborne effluents do not exceed maximum permissible concentrations (MPC) as set forth in the United States Nuclear Regulatory Commission (USNRC) radiation protection standards. This simply means that any effluent that could possibly contain radioactivity must be monitored. Besides the legal implications, sound industrial hygiene practices require that personnel be protected against the possibility of exposure to excessive radiation from any source. Off-line gas monitors are frequently used in conjunction with particulate monitors. This is particularly the case with a stack or duct where effluent is released into the environment. Used in this manner, the particulate monitor serves as a pre-filter for the gaseous monitor and also as a monitor for airborne radioactive particulates. Where an off-line gas monitor is used independently, without the aid of a particulate monitor, a separate filter assembly is installed to prevent contaminated particulate buildup inside the sensitive volume. The off-line effluent monitor incorporates its own pumping system to insure a positive displacement of the effluents being monitored. Off-line effluent monitoring is normally utilized where optimum geometry is desired to gain maximum sensitivity. Scintillation detectors are used because of their sensitivity and reliability.

  • Off-line airborne effluent monitoring skid
  • Measures and reports airborne radioactive releases from stacks and ducts
  • Quantifies airborne particulate, radioiodine and gaseous effluents
  • Compatible with Model 943 Series detectors and Model 942A Series digital ratemeters or Model 960 Series electronics


The sample is withdrawn from the process stack/duct via isokinetic nozzles (when required), through customer’s sample line to the inlet of the sampling skid. The sample passes through the particulate and iodine filters, then through the gas sample volume to the pumping system and back to the process stack/duct. The sample flow is controlled by a manual set point, or ratioed to stack/duct flow for The detector output signal is transmitted to the Universal Digital Ratemeter. The particulate ratemeter displays gross particulate counts, the iodine ratemeter displays iodine counts as determined by the preset window of the single channel analyzer, and the gas ratemeter displays gross noble gas counts, compensated for changes in pressure at the volume chamber. These ratemeters also provide output alarm contacts for Alert, High Radiation, Channel Fail, and when required Rate Of Rise for fixed filter application. A Low Flow alarm is also available for the sample stream. Check source actuation is manual from the ratemeter, with alarms muted when in the check source mode.


Model Name


940-1 Off-Line Airborne Effluent Monitor, includes: Open-frame sampling skid, with the following components mounted, plumbed and wired:Gas sampler, fixed volume, with 4 pi lead ielding, Model 841-334 Particulate/Iodine samplers, as required, with 4 pi lead shielding Scintillation type detectors, as required Pressure transmitter upstream of gas sampler for automatic compensation of count rate for gas density Mass flow controller for isokinetic sample flowrate control Positive displacement pumping system Valving and plumbing, as required Isokinetic gas nozzle assembly for the stack/duct (when required) Universal Digital Ratemeters, local or remote mounting
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