Fluke Biomedical 1060AM - Manual (Page 21)

Theory of Operation
General
4
4-1
Section 4
Theory of Operation
4.1 General
4.1.1 Detector Input
The Model 1060 has four separate input terminal points, one for each type of detector: Geiger Mueller
tube, proportional tube, BF
3
tube, and photomultiplier/scintillator. These points are inputs to analog
circuits that condition the signal pulse from the detector. The conditioned pulse is then input into the
"Clock2" input of the Intel 80C196 microprocessor. The microprocessor counts both the rising edge and
the trailing edge of the signal pulse.
4.1.2 High Voltage Supply
The Model 1060 takes the +5 VDC power and utilizes a switching power supply and a step up transformer
to produce a range of voltages from 500 to 2500 VDC. A 1000:1 divider provides feedback for regulation
of the high voltage. The high voltage is digitally controlled with a resolution of 1 V. A 12-bit analog to
digital converter provides the high voltage setting to the microprocessor. The microprocessor has the
ability to completely shut off the high voltage.
4.1.3 Auxiliary DC Power
A +/- 12 VDC power is provided via a switching power supply from the +12 unregulated input power. This
voltage is available at an edge connector to provide power for detectors that contain preamplifiers. The
output of this supply is 50 mA. A non-inductive load is recommended.
4.1.4 Jam Detection
The low discriminator output is buffered and charges a capacitor through an RC network. This voltage is
then monitored by one of the 8 analog input channels of the microprocessor. At a predetermined voltage
threshold corresponding to a high-count rate, approximately equal to twice the detector maximum, and/or
approaching continuous discharge, the microprocessor will shut down the high voltage and indicate that a
jam condition has occurred.
4.1.5 Thresholds
An upper and lower threshold provide an energy window for pulses. The microprocessor will only
recognize those pulses within the magnitude established by the thresholds. The range of the lower
threshold is from 0 to 1.25 V.
The range of the upper threshold is from 0 to 7 V and must be higher than the lower threshold. The upper
threshold may be disabled if desired. Both thresholds are under software control. The resolution of the
upper and lower thresholds are 25 mV and 5 mV respectively.
4.1.6 Analog inputs
There are 8 analog inputs, but two are reserved, one for jam detection and one for local temperature measurement,
usually, the detector. The other 6 are made available to the user on an edge connector. The input range is 0 to 5 V DC,
with 10-bit resolution. Typical uses for these inputs are for process transducers. All are read by software.