Model FP400


  • Portable tritium air monitor with fast and accurate response
  • Fast, sensitive, and stable response, requiring just 12-15 seconds to reach 90% of final reading
  • Cruciform gamma compensation (220cc volume)
  • Sensitivity: 5 µCi/m3, 0.2 MBq/m3
  • Range: 1 to 19,999 µCi/m3 or 0.1 to 1,999.9 MBq/m3 (DAC, MPCa, and µSv/h also available)
  • Audible and visual alarm indicators for low flow, low battery, and signal level
  • High voltage power supply malfunction alarm
  • Alpha pulse suppression, radon rejection
  • Offset potentiometer control included
  • CE Marked


The Model FP400 is a “fast purge” version of the Model 400SBDyC.  Includes four small 110cc ionization chambers and a faster pump (2-4 LPM) to provide a quicker response rate, requiring just 12-15 seconds to reach 90% of the final reading.   The cruciform chamber geometry provides nearly perfect gamma compensation regardless of photon energy, flux gradient, or flux direction.  Two ion chambers are used for measurement (220cc total) and two for gamma compensation (220cc total).  Useful for applications which require low-level sensitivity and extremely fast and stable response.  In comparison, the Model 400SBDyC utilizes four 200cc ionization chambers and a pump rated for 1.5 – 2 LPM.

Power is supplied by a pair of “D” size alkaline or NiMH rechargeable batteries.  Onset of the battery depletion is signaled by illumination of an LED located next to the meter face.  This same LED will also signal red when there is a malfunction with the high voltage power supply.  A nine-position alarm level stepped attenuator, adjustable over partial scale (2 to 1,000 µCi/m3) is located on the front panel.  A steady tone is emitted by an acoustic signaler if the measurement exceeds the alarm set-point (illuminates red LED), or if the sample airflow has been interrupted and is too low (illuminates yellow LED).  The alarms are non-latching.

Zero adjustment is unnecessary, the electrometer is completely temperature stable and shows zero drift from 0° C to 50° C due to special design and careful selection of an ultra-high impedance semiconductor with low internal current leakage and long-term DC stability.  The FP400 can reliably measure currents as low as 10-16 amperes and the span calibration is permanently stable.  The ionization chamber polarizing voltage is supplied by an electronic low-noise regulated dual high-voltage power supply (±80VDC).  The FP400 includes proprietary radon recognition and elimination circuitry to provide accurate, fast, and drift-free measurement.

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