Model 400AC


  • High-performance portable tritium air monitor with upgraded features
  • Gamma compensation ON/OFF toggle switch for easy gamma source calibration
  • Automatic recalibration software
  • Cruciform gamma compensation (400cc volume) with virtually no offset in fields up to 10 mR/h
  • Sensitivity: 2 µCi/m3, 0.1 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
  • RS-232 Data Output
  • No long-term drift, no manual zero adjustments
  • Offset potentiometer control included
  • CE Marked


The Model 400AC is based on the popular Model 400SBDyC and is a small, lightweight portable tritium in air monitor with a few additional upgrades, including a gamma compensation on/off toggle switch for easy gamma calibration, NiMH rechargeable batteries, RS-232 data output, and automatic calibration software.  Four 200cc ion chambers arranged in a cruciform geometry provide nearly perfect gamma compensation regardless of photon energy, flux gradient, or flux direction. Two ion chambers are used for measurement (400cc total) and two for gamma compensation (400cc total). The Model 400AC is unequaled in sensitivity, stability, speed of response, and gamma compensation.

Power is supplied by a pair of “D” size NiMH rechargeable batteries. The onset of the battery depletion is signaled by the 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 a 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 the special design and careful selection of an ultra-high impedance semiconductor with low internal current leakage and long-term DC stability. The 400AC 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 400AC includes proprietary radon recognition and elimination circuitry to provide accurate, fast, and drift-free measurement.

Options: Hard Plastic Protective Carrying Case

For Technical Specifications click here.