EXPO MiniPurge D770/ET, Руководство пользователя

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is complete. This performs two functions: to turn on the electrical supply to the pressurized enclosure
and to reduce the high purge flow rate to leakage compensation mode. It also provides a hold-on signal that
maintains the leakage compensation mode with the power switch on, even when the purge timer has reset ready
for the next purge cycle.
OR Gate
This device provides the Purge Complete Valve with the hold-on function referred to previously. When either the
timed-out signal or the purge complete signal is present it allows the pilot signal to be sent to the purge complete
valve.
Alarm Only Circuit (/AO)
If the pressure in the pressurized enclosure is too low the system will normally cut off electrical power to it. In
certain circumstances, where local codes of practice allow, the system can be altered to provide a hold-on circuit
that will maintain the electrical power supply to the pressurized enclosure while also providing a pressure failure
alarm. The user must respond to the alarm and either restore the pressure to the pressurized enclosure or
otherwise make the installation safe; for example, cut off the electrical supply. The decision to use the Alarm Only
facility, and the allowable length of time for non-pressurized operation, is the responsibility of the user.
Warning: It is potentially dangerous to energise the pressurized enclosure in an non-pressurized
condition when it is known that there is potentially explosive gas or dust in the hazardous location.
Visual Indicators
Visual indicators are fitted to provide status information to the operator.
* The Green / Black combination indicates normal operation of the pressurized enclosure after the initial
purging cycle has been completed.
Power Interlock Switch
This flameproof power switch is activated by the signal from the Purge Complete Valve. This activation can be
used to turn on the electrical supply to the pressurized enclosure. The cable from the switch is terminated in the
/PA terminal box.
Alarm / Pressurized Switch
This flameproof switch is operated by the pressurized signal. It allows a remote electrical system status indicator
to show either pressurized or a pressure failure alarm. The cable from the switch is terminated in the /PA terminal
box.
System Purging Switch (Optional)
This switch is operated by the purge flow signal that allows a remote electrical system status indicator to signal
that the system is purging; sometimes referred to as purge in progress. The cable from the switch is terminated
in the /PA terminal box.
Alarm / Pressurized Indicator
Green* Pressurized
Red Pressure Alarm (enclosure pressure low)
System Purging Indicator
Black* Purge flow too low (not in purge mode)
Yellow (flashing) Purging (flow above minimum)