
Chapter Three: Overview
Front Panel Controls and Indicators
25
Front Panel Controls and Indicators
Power Switch
In the “On” position, the power switch applies power to the PDR unit.
Display (DVM)
The 4½ place voltmeter accepts 1.9999 Volts full scale. This meter contains its own power supply,
and provides display information in BCD form to the rear panel. Decimal point information for the
display is obtained from rear panel range rocker switches and internal decoding circuits used in
conjunction with the engineering units switch.
Zero Adjust Control
These controls are used as fine zero adjustments for the pressure gauge. An absolute pressure
gauge must be pumped down below its resolution before this adjustment can be made; differential
gauges should be cross-ported. The zero control on the pressure sensor is used as a coarse zero.
Set Point Adjust Controls
These controls are used to adjust the desired set point level. Range is from 0 to 100% of the full
scale pressure.
Read Set Point Switch
This switch connects the pressure signal to the engineering units circuit and ultimately to the
display when it is in the center position. When it is switched toward one side or the other it
connects the appropriate set point level through the engineering units circuit to the DVM. Thus the
set point level is displayed in the same pressure units as the gauge being used. The switch is spring
loaded to return to the center position when released.
Set Point Relay Indicator Lamps
These LED’s are illuminated when the set point relay is energized. This will occur when the
pressure signal is below the set point value.
Engineering Units Selection Switch
This rotary switch is used for selecting which engineering units should be used with the front panel
display. Changing this switch will automatically scale the display to the right value and move the
decimal point to the appropriate location in the display.
x10
-3
Lamp
This LED indicates when the display is showing units requiring multiplication by 1/1000.
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