WBJI DSM-502
PAGE 5
3.3
HIGH & LOW VOLTAGE POWER SUPPLIES
Six "AA" size batteries provide the LOW VOLTAGE power for all of the DSM-502 circuitry. The batteries
are connected to a positive power regulator on the POWER SUPPLY pc board designated E1. E1 converts
the 9 vdc to a very 5 vdc. The output of E1 (+5 vdc) is connected to the circuitry req5 vdc and
the negative 5 vdc regulator U2. The output of U2 (-5 vdc ) is connected to the circuitry requiring -5 vdc.
Both power regulators (E1 & U2) have very good regulation
±
.5% and a low temperature coefficient. The
HIGH VOLTAGE supply is comprised of a special high efficiency transformer with a feedback winding and
oscillator circuitry to generate a low ripple, stable high voltage. The output of the transformer T1 is
connected to a voltage doubler circuit comprised of D1-D4 & C3-C7. The output of the doublers circuit is
filtered in a pi type filter and connected to the PROBE BNC through R1. R1 is also the load resistor for the
detector circuit. The HV oscillator circuit through R4 constantly monitors the high voltage. R4 provides U1
a low voltage signal that represents the high voltage. Any change in the high voltage will result in an
appropriate increase or decrease in the power Q1 & Q2 provide the high voltage transformer. This
"feedback" is utilized to regulate the high voltage to approximately
±
1%. The power supply is designed with
two high voltage outputs that can be independently adjusted between 300 – 1500 vdc. Figure 3 show the power
supply pc board’s major components and calibration controls
4.0
OPERATING CONTROLS & INDICATORS
4.1
CONTROLS - MAIN FUNCTION SWITCH
CONTROL SETTING FUNCTION
OFF
ALL POWER IS DISCONNECTED TO THE INSTRUMENT
RATEMETER
NORMAL OPERATING RATEMETER MODE – CPM OR DOSE
(BASED ON CS137 CALIBRATION)
COUNT
TIMED COUNT (SCALER) MODE FOR INTERNAL PROBE
4.2
CONTROL – DOSE /CPM
Selects the operating mode of the ratemeter to measure in either roentgen or sieverts (BASED ON CS 137
CALIBRATION) or counts per minute. Probe response is automatically displayed in the correct (micro,
milli or R/hr or sieverts) DOSE mode for the probe that has been selected on the MAIN SELECTION
SWITCH.
4.3
CONTROL – SPEAKER/ZERO
Control is momentary toggle switch with the center neutral. Momentary operation in speaker direction turns
speaker on or off. Momentary operation in zero direction instantly disables the AUDIBLE OPERATIONS
ALARM. THE AUDIBLE ALARM WILL REMAIN DISABLED UNTIL THE SIGNAL FALLS BELOW
THE SETPOINT AT WHICH TIME THE ALARM CIRCUIT WILL RETURN TO NORMAL
OPERATION. OPERATION OF THE SWITCH IN THE ZERO DIRECTION FOR AT LEAST 3
SECONDS WILL ZERO THE INDICATION ON THE LCD
4.4
CONTROL – DATA/BACKLIGHT
Control is momentary toggle switch with the center neutral. Momentary operation in data direction provides
the data being displayed on the LCD to the RS-232 DATA OUTPUT CONNECTOR.
Momentary operation in the BACKLIGHT direction will light the LCD BACKLIGHT FOR 30 seconds.
BACKLIGHT switch can be operated at the end of each 30 second cycle for another 30 second period for as
long as necessary. Continued operation of the BACKLIGHT will greatly reduce the instruments battery life.
