Ultra-high meg ohm resistors, certified to about 1 % precision, used for electrical calibration (or verification) of the tritium monitors response.

Electrical calibration involves using a calibrated resistor and injecting a known electric current directly to the Overhoff ionization chamber electrometer module which is fitted with a BNC receptacle.

Knowing the effective volume of the ionization chamber and using Ohm’s law, a voltage value can be calculated based upon the precise resistance and the specified simulated ionization current.  While this method is especially useful for calibration at high levels since it is undesirable to work with high levels of radioactive tritium gas, electrical calibration is certainly valid for all levels of measurement.