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TELEDYNE API
Theory of Operation M703E Calibrator Operator’s Manual
9.2.3. RELAY PCA
The relay board is one of the central switching and power distribution units of the calibrator. It contains power
relays, valve drivers and status LEDs for all heated zones and valves, as well as thermocouple amplifiers, power
distribution connectors and the two switching power supplies of the calibrator. The relay board communicates
with the motherboard over the I
2
C bus. Its status indicators and components can be used for troubleshooting
power problems and valve or heater functionality.
Generally, the relay PCA is located in the right-rear quadrant of the calibrator and is mounted vertically on the
backside of the same bracket as the instrument’s DC power supplies, however the exact location of the relay
PCA may differ from model to model (see Figure 3-3.)
Power
Connections
for DC
Heaters
Status LED’s
(D2 through D16)
DC Power Supply
Test Points
Watchdog
Status LED (D1)
I
2
C Connector
DC
Valve Control
Drivers
AC Power
IN
DC Power
Distribution
Connectors
DC
V
alve &
Photometer
Pump Control
Connector
A
C Power
OUT to Dry
Air Pump
AC Pump
Configuration
Plug
Dry Air AC Pump
Control Relay
DC Valve &
Photometer
Pump
Control
Figure 9-4: Relay Board PCA with AC Relay Retainer Removed
This version of the Relay PCA include one AC relays that controls the AC-powered Dry Air (zero air) pump and
A plastic insulating safety shield covers the remaining empty AC Relay sockets.
CAUTION
NEVER REMOVE THIS SAFETY SHIELD WHILE THE INSTRUMENT IS PLUGGED IN AND
TURNED ON. THE CONTACTS OF THE AC RELAY SOCKETS BENEATH THE SHIELD
CARRY HIGH AC VOLTAGES EVEN WHEN NO RELAYS ARE PRESENT
140 05744 Rev B