Service manual

LUMISCAN ACR-2000 SERVICE MANUAL - SECTION 4.0 THEORY OF OPERATION
4-13
4.5.3 PMT PREAMPLIFIER
The preamplifier is the interface between the PMT receiving the stimulated light from the collection
chamber and the log processing circuits in the Data Acquisition PCA. The preamplifier serves as a
current to voltage converter between these two assemblies.
The preamplifier is a single integrated amplifier with the input power and common return provided
from the Data Acquisition PCA. The input power is filtered at the amplifier and reverse bias diodes
are provided to protect the circuit against improper connections of the input power. High voltage
from a PMT supply is divided in 10 equal differential voltages and used to bias the cathode, grid, and 8
dynodes of the PMT.