| 摘要 |
For use with a photomultiplier tube responding to gamma ray induced scintillation pulses in a well logging sonde, a system having the preferred and illustrated embodiment of an input amplifier DC connected with a differential amplifier output to an integrating amplifier. The integrating amplifier is output to another differential amplifier then output to a sample and hold amplifier. This provides the input for a successive approximation digitizer. A feedback loop is incorporated in the system connected from the output of the integrating amplifier. It detects an error component due to noise, offset voltage, and drift accumulated at the integrator. It comprises a track and hold amplifier which is output to a pair of voltage comparators, one determining an excessive negative value and the other determining an excessive positive value. The two comparators are input to appropriate up and down terminals of a bidirectional counter. The counter is output to a digital to analog converter which forms a feedback analog voltage for the differential amplifier. The scintillation pulses are integrated over a specified time interval. That value is digitized after selection by the sample and hold amplifier. Moreover, base line drift is eliminated by operation of the feedback loop. |
