Specifications

Electronic Pressure Control (EPC) Module, Continued
The EPC is made up of a printed circuit board with two pressure
transducers, two proportional valves with associated electronic circuitry,
manifold for pneumatic connections, PC connector for communication
signals and a DC power connector. Refer to Figure 2-20.
Electrical
The EPC provides electrically controlled pressure for helium, hydrogen
and nitrogen carriers etc., as well as low flow and low pressure (<100
psi) applications such as flame detector fuel. The EPC operates from
+24VDC at 4 watts. Electrical connections are made using plug type
connectors.
The EPC receives commands from the Embedded Sensor Near
Electronics (EMSNE) software via I
2
C bus regarding timing and pressure
setpoint. The timing of messages from the EMSNE software controls
timing within the EPC. There is no time base in the EPC. Module control
is established by sending parameters, such as setpoint pressures and
ramp rates to the EPC. The EPC is used in the Maxum II to control the
carriers and/or fuels for the detector modules. The EPC can also be
used in field-mounted installations.
The EPC communicates with other components via the I
2
C bus and
communicates actual pressure back to the EMSNE software. Regulated
pressure range is 5-100 psig.
Each EPC channel consists of a pressure sensor amplifier and analog
filter followed by an A/D Converter. The converter is read by the local
controller that calculates a new control value used to control the
proportional solenoid valve.
Channels
Control parameters, such as set-point pressures are sent, via the I
2
C, to
the EPC. Status and diagnostic data is available via the I
2
C bus.
The initial control parameters and calibration parameters are stored in
CIM On-Board non-volatile memory. With this type of memory, data is
not lost in the event of a power failure or turning system power off.
Non-Volatile Memory
EPC diagnostics are read-back of setpoint pressure via the software, DC
power within operating limits, monitoring of line and short-term pressure
variations with respect to the setpoint regulation, out of range pressure
alarm and a diagnostic failure.
Diagnostics
2-30 A5E31405710001