Chapter Three: Overview Process Limit Relays
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Process Limit Relays
There are two process limit (PLO) relays in the 651 controller. Each relay has a high and a low
trip limit. Refer to Table 8, for the Interface connector pinout, to determine which pins are for
relay 1, and which are for relay 2. Use the appropriate pins to configure the relays for normally-
open or normally-closed operation. While the pressure remains within PLO limits, the 651
pressure controller actuates the relay (a normally-open contact closes, and a normally-closed
contact opens). When the pressure crosses below the low trip point or above the high trip point,
the 651 pressure controller de-actuates the relay (a normally-open contact opens, and a normally-
closed contact closes).
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