Abstract: Method and apparatus for calibrating a gamma counter, such as a fibrinogen monitor, employing a pulse-height analyzer and a control circuit to determine the optimum high-voltage setting on the photomultiplier tube of a scintillation counter. A first pair of upper and lower pulse-height levels are automatically selected and counts measured to determine if the spectrum of the radioactive source is positioned correctly in the pulse-height domain. A series of measurements are made with differing high-voltage settings to ascertain the desired location of the spectrum. A second pair of upper and lower levels is provided for use in the actual monitoring operation and is automatically set after each calibration operation.

Abstract: A background subtractor circuit is disclosed for subtracting a preselected number of pulses from a train of input pulses. Switches are provided whereby the operator selects the background pulse rate, attributed to environmental factors, and wherein a train of background pulses are subtracted, at a preselected rate, from the incoming pulse train.