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The PMPCO is an automatic change over two
relay output module for use with Direct Digital Controllers or in a stand-alone
mode with demand signals such as time clocks. Applications include the
control of heating pumps, chilled water pumps and any other duty standby
application, where automatic load change-over is required. LEDs indicate
relay output status and on board jumpers select Auto/On/Off. |
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Description of Operation
Normal Operation
The module is designed for a permanent 24 Vac power supply, on initial power
up and the enable input UI-1 present for 4 secs, the module will select
load 1 as lead and energise relay 1.
The input UI-2 monitors the DP or water flow switch, after an adjustable
DIP switch selectable delay, the input must be closed.
Differential Pressure Switch (DPS) Fault Operation
Bit switch SW2 needs to be set in ON position to enable Differential Pressure
monitoring. Using bit switches SW3 and SW4 the required delay time for the
DPS is set (15, 30, 45 or 60 seconds).
If the UI-2 Differential Pressure (DP) input has not closed after the delay
time, the lead relay will de-energise and the lag relay will be energised.
The UI-2 DP input will again be monitored, if the input does not close,
lag relay will remain energised and the green LED will flash indicating
fault. If the DP closes the lag load will remain energized and the green
LED will be flashing.
During the normal operation when the enable input UI-1 is closed and if
the UI-2 pressure switch opens, the lead relay will de-energise and the
lag relay will be energised.
Load Fault Operation
The inputs DI-1 and DI-2 monitor their respective loads, if Load 1 is lead
and the input DI-1 opens, then Relay 1 will de-energise and Relay 2 will
energise, this condition will remain until the fail reset switch has been
pressed (or power to the unit is cycled).
If Load 2 is lead and the input DI-2 opens then Relay 2 will de-energise
and Relay 1 will energise, this condition will remain until the fail reset
switch has been pressed (power to the unit is cycled).
In both cases the green LED light will flash indicating fault.
Fault Reset
Once the lead load fault has been cleared and the fail reset switch has
been pressed the lag relay will de-energise and the lead relay will energise
and the green light will be ON. The fault state can also be reset by cycling
the power to the pump change-over module after which the relay 1 will be
selected as a lead load.
Remote Changeover of Loads
Mode 1
The lead load can be changed via the digital input DI-1, if the DI-1 is
opened for more than four seconds and closed again within ten seconds the
loads will changeover.
If the digital input DI-1 remains open for more than fifteen seconds then
both loads will de-energise.Upon digital input DI-1 closing then the load
that was lead will again energise.
Mode 2
The lead load can be changed via the digital input UI-1. If the UI-1 is
opened for more than four seconds and closed again within ten seconds the
loads will changeover.
Differential Pressure
Switch
The input UI-2 DP switch can be disabled via the DIP switch setting, load
changeover is then achieved by change of state on the digital input DI-1.
Power Fail Restart
On returning from a power failure relay one will be selected as lead.
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