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General Information
General Description
1
1-
1
Section 1
General Information
1.1 General Description
The Victoreen
®
Model 943-227-15 Digital Preamplifier, is designed to operate with the Model 943-27,
Current Mode Beta Scintillation detector and the Model 942A-200C Series Digital Ratemeter (UDR) or the
Model 960 Series Digital Process Control system. When connected to the beta sensitive scintillation
detector, it comprises a monitoring system which operates in the range of 10
-3
to 10
5
uCi/cc (or 1E
0
to 1E
8
Pico amperes). The UDR provides display, control, and annunciator functions for the monitoring system.
The preamplifier contains a microprocessor controlled, auto-zeroing, integrating electrometer, a
programmable gain amplifier, an analog-to-digital converter and an asynchronous serial communications
interface. Communications with the UDR is accomplished via the optically isolated Victoreen Serial
Communication Loop driver/receiver circuitry.
Interconnection of the detector and preamplifier is accomplished utilizing two, six (6) foot coaxial cables.
One cable supplies the high voltage for the detector (negative polarity). The other cable is used for the
detector output signal. Interconnection between the preamplifier and the UDR or 960 system is
accomplished via a six-conductor cable and a high voltage coaxial cable.
The detector operates at a potential of approximately (-) 500 VDC, and produces a nominal DC output
current of 1 x 10
-12
amperes to 1 x 10
-4
amperes. Depending on sampling geometry and detector set up,
this corresponds to a range of 1 x 10
-3
to 1 x 10
+5
uCi/cc.
The preamplifier is a self-contained electronics unit that processes the DC input signal from the detector,
digitizes the signal, and transmits the digitized value to the readout via a modified RS232C compatible
serial data communication port. It contains two printed circuit boards (mounted on the rear of the
enclosure cover, a terminal block for terminating the field cable from its associated controller and two
connectors for terminating the detector Signal and HV coaxial cables. The larger of the two printed circuit
boards is the 977-210-10M Serial Interface board. This board controls the communications with the
controller. The smaller board is the 977-200-15M Electrometer. It contains the microprocessor and
associated circuitry for converting the detector output current into a digital value.
For additional information on the detector or readout device, refer to the instruction manual for the Model
943-27-31 detector, the Model 942A-200C UDR, or the applicable Model 960 System manual.
1.2 Application
The Model 943-227-15 Digital Preamplifier is used with the Victoreen 942A-200C or Model 960
microprocessor based radiation monitors. The Model 942A-200C or 960 system provides the +15 VDC
preamplifier electronics power, (-) 500 VDC detector power and the RS232C serial communications
support. The digital preamplifier is available in two serial port configurations. For applications less than
50 feet, the Model 943-227-15, configured for RS232C communications, is used. For applications
requiring signal transmission distances of up to 1 mile, the Model 943-227-15VL, configured for Victoreen
Loop communications is used. Table 1-1 is a list of available configurations and compatible 9XX series
equipment. Please contact Fluke Biomedical Radiation Management Services for additional information.