A sewage treatment plant needed to automate the start-stop of a large pump/grinder motor. The existing application used a tank level meter to signal the start-stop of the motor. However human intervention was frequently required to manually override the motor stop mechanism to allow it to continue to operate after the tank was emptied to assure the grinder portion was clear of old debris that would cause a possible stall on the next start.
After hearing about the considerations of this application, one of our Hardware and Software Engineers recommended the model SPA2 because of its multiple conveniently defined start-stop thresholds and adjustable stop delay.
With the SPA2, Alarm #1 is routinely configured as a ‘High Alarm’. In this pump/grinder motor application, this configuration can start the motor when the tank level exceeds the prescribed threshold level. This alarm relay output activates an external DPDT high current contactor (relay) coil with one set of high current rated contacts providing power to the motor/grinder. A second set of contacts is wired in series with alarm #2 contacts providing a latch to keep the contactor engaged.
Alarm #2 is routinely configured as a ‘Low level’ alarm. Using this configuration in the application allows the relay to change state upon the tank low level being achieved. However, the alarm is also programmable with a ‘Delay’ setting of up to 120 seconds thereby providing the desired further draining of the tank a prescribed amount as desired. At the conclusion of the ‘delay’ the alarm #2 relay contacts change state and ‘unlatch’ the high current contactor.
Programming the two SPA2 alarms takes about as much time as is required to read this application. Note the simple wiring:
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