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6.2.2. Valve Purge Routine
When a purge routine is called either by clicking the ‘Purge’ button or calling the routine via an
interface, the following procedure is followed:
Step
Function
1
Actuate C1 valve to move the scanner to cal / purge.
2
Wait 1 second.
3
Vent C1 valve.
4
Wait 0.5 second.
5
Set the internal purge valve to on
6
Wait the time value set ‘valve Control’ (5.9.3). The default is 10 seconds
7
Vent the purge valve
8
Wait 1 second.
9
Actuate C2 valve to move the scanner to run mode.
10
Wait 1 second.
11
Vent C2 valve.
NOTE : Step [8] in the above routine is there to allow any purge pressure to dissipate before the
scanner is returned to RUN mode. It is there for the instance that a high purge pressure is used
where there is a possibility to charge a blocked measurement line to this pressure. When the
scanner is returned to RUN mode, the differential transducer would be exposed to this pressure and
could be damaged.
If purging is to be carried out with pressures present on the measurement lines (for example in
flight) then this routine could lead to a situation where this pressure is fed back through the
measurement lines, scanner and venting purge valve for this time period (1 second). This is reverse
purging and should be avoided as it can bring contaminants into the flightDAQ2. If purging is to be
carried out with pressures on the measurement lines then this routine should NOT be used and the
valve sequencing carried out manually without a purge vent before the scanner is returned to RUN
mode. In this instance, the purge pressure should be limited to the full scale of the differential
scanner.
