Kipp&Zonen Brewer MkIII - Manual (Page 23)

MKIII SERVICE MANUAL 18
4.11 RATEMETER
The ratemeter circuit provides a voltage output of the photon count rate. It consists of a two-
transistor charge pump on the high speed amp board, and an integrator-amplifier on the Main
Electronics board. A transistor is connected as a current pump and driven by one of the outputs of
a J-K flip flop on the high speed amplifier board. The pulses from the flip flop are integrated by an
RC network then scaled by an op-amp.
4.12 TEMPERATURE MONITOR
The temperature monitor is a temperature sensitive bridge using YSI linearized thermistors. The
bridge output is amplified to produce a suitable scale for the A/D converter. There are six thermistor
circuits available, one of which is located in a hole drilled in the side of the front flange of the PMT
housing. The other five are used to measure temperature at points around the instrument as status
information. One of the sensors monitors outside temperature.
4.13 HIGH VOLTAGE CIRCUITS
The high voltage (600-1600 volts) for the photomultiplier (PMT) is provided by a DC-DC converter /
high voltage control circuit board.
4.14 CLOCK / CALANDAR
The real time clock/calendar circuit is a battery backed up clock with integral static random access
memory. A lithium battery is used to keep the clock operating when there is no power applied to
the Brewer. The clock is year 2000 compatible.
4.15 A/D CONVERTER
The A/D converter has a 10-bit conversion resolution and is built into the microprocessor. Analog
multiplexers are utilized to select the channel to monitor. The AP routine is the main routine that
accesses the data and displays the information on the PC monitor, saves it to a file, or prints it on
the printer.