Model 421


  • Modular configuration is highly customizable
  • Wide measurement range up to 6.5 decades, dual or quad ion chambers for gamma compensation
  • Select ion chamber size: dual 2L or quad 2L
  • Upgraded alarm system: two adjustable tritium level alarms, latching and non-latching alarm modes, optional malfunction and low flow alarms, and up to 3 alarm relays (two-level, one malfunction)
  • Visual and audible alarm indicators
  • Alpha pulse suppression, radon rejection
  • Long-term zero stable, span calibration is permanently stable due to special electrometer design
  • Remote mounting of ionization chamber (25 feet standard)


The Model 421 features a wide measurement range of up to 6.5 decades with dual or quad ionization chambers for gamma compensation.  Useful for accurately measuring low levels of tritium across a wide range, even in areas with an elevated gamma background.  The Model 421 is part of our modular series, designed for easy customization, and features an upgraded alarm system that includes two adjustable tritium level alarms (alert level and high level) with audible and visual alarm indicators, acknowledge (mute), latching, or non-latching alarm modes, and up to three alarm relays (two-level relays and one malfunction relay).  Optional alarm indicators include: low flow alarm and malfunction alarm (low voltage failure, high voltage failure, or electrometer failure).

The Model 421 typically supports two different chamber sizes, depending on your range and sensitivity requirements, select either dual 2L chambers or quad 2L chambers.  Quad 2L ionization chamber assembly arranged in a cruciform geometry provides the best sensitivity, stability, and omnidirectional gamma compensation.  Ionization chambers can be mounted remotely (up to 25 feet standard), or locally inside the electronics enclosure.

Typical Measurement Ranges:

Ci Bq
Dual 2L: 1 to 199,999  µCi/m3 0.01 to 1,999.9  MBq/m3
Quad 2L: 0.1 to 19,999  µCi/m3  0.01 to 1,999.9  MBq/m3

A wide variety of options are available, including: choice of data outputs (RS-232, Ethernet, 4-20mA), pump type and flowmeter assembly, system failure monitor, low flow alarm, remote display unit, helium leak testing, wire-grid ion chambers, gold-plated measurement chamber, HTO only measurement (noble gas compensation), and more.

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