Harris Atlas DVL400 Technical Manual page 144

Section 4 Theory of Operation
4.6.4.4.6 K7, Interlock Relay
The transmitter always has final control over the pump module via K7, the Interlock
Relay. There is an interlock control relay located on the External I/O Board in the
transmitter which must be closed for the pump module to operate. When closed it
sends +34Vdc to the cooling control panel through X2 pin 3 to close relay K7. K7
has one contact that will enable or disable contactor K3 and K4 (the pump motor
contactors) and another contact which will light the Interlock LED H4 when the
interlock control relay is opened. K7 is shown in the non-energised position which
would shut the pump module off.
For normal operation, K7 contacts would be opposite of that shown on the
schematic. This would shut off the interlock LED and enable K3 and K4.
4.6.4.4.7 K6 and K8, Coolant Level Relays
The pump module reservoir has 2 level switches, one for a warning to the control
panel and transmitter and a lower level switch which is used as a coolant fault to
shut the transmitter and pump module off.
When the coolant levels are sufficient, the coolant switches will be open. This
will leave K6 and K8 relaxed and their contacts in the position shown on the
schematic for normal operation.
K6 is the Coolant Warning relay. If the coolant level drops below the warning level
but is still good enough to operate the transmitter, K6 will energise. This will switch
both of its contacts. One contact will light the Coolant Low LED, H6 while the
second contact will pull the transmitter status line low (to ground).
K8 is the Coolant Fault relay. Under normal operating conditions, the K8.1 contact
is supplying 24Vac to the interlock relay K7 and therefore the motor contactors K3
and K4 (provided K7 is energised). If the coolant level drops below the fault level,
K8 will energise, switching both of its contacts. One contact will pull the transmitter
Coolant Fault status line low shutting off the transmitter. The other will remove the
24Vac from K3 and K4, shutting off the pump module. This contact is now in the
opposite position of that shown on the schematic and is lighting the Coolant Fault
LED H5 on the front of the Pump Control Panel.
NOTE:
Since the coolant level switch logic uses open switches to sense a no fault
condition, these contacts should be tested as part of a routine maintenance
schedule. This will confirm proper operation and test for defective switches
and/or open connections in the cable interfacing the pump module with the
pump control panel.
4-44
WARNING: Disconnect primary power prior to servicing.
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ATLAS Series™
2/25/03