| 摘要 |
PURPOSE:To make measurement with high accuracy by varying either of the high-voltage level and discrimination level to be supplied to a photo multiplier and detecting a plateau part from the prescribed counting result of a counter. CONSTITUTION:A lighting control signal 20a is outputted from a control circuit 20 and a light source 24 for adjustment is lighted. A pulse signal 12a of the crest corresponding to the prescribed level of a supplied high voltage 14a is outputted in the photomultiplier 12 when a standard lumimous flux is made incident to the multiplier 12. The prescribed discrimination level Vt is previously set in a discrimination circuit 16. The circuit 20 detects the plateau part by varying the input signal 12a in a preset range and storing the pulse number N to respective voltages, i.e. the results of counting of a counter 18 and sets the level of the high voltage 14a in such a manner that the level Vt comes in the valley part of the crest value distribution. As a result, the high-voltage level is variably controlled and the deviation between the discrimination level and the crest value distribution is automatically corrected. The measurement is thus made with the high accuracy.
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