Chapter Three: Overview Trip Points
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Trip Points
The 640B Series controller provides two trip points (Trip Point A and Trip Point B). Each trip
point operates independently and controls an open collector output that can be connected to an
external relay. Each trip point has an adjustment pot, a status LED, and a test jack. Refer to
Figure 11, page 31, for the location of the trip point adjustment pots and LEDs. The test jacks are
located on the side of the unit, as shown in Figure 4, page 18. Refer to How to Adjust the Trip
Point Values, page 44, for instructions on changing the trip point values.
Action of the Trip Points
The trip points can be turned on when the pressure is above or below the trip point value,
depending upon the location of jumpers on the Transducer board. The initial configuration is:
Trip Point A is set to trip high; it is on when the pressure is above the trip point (it is off
when the pressure is below the trip point value)
Trip Point B is set to trip low; it is on when the pressure is below the trip point (it is off
when the pressure is above the trip point value)
When on, the trip point is connected, through the collector of an NPN transistor, to power ground.
Refer to Trip Point Specifications, page 52, for the ratings. You can use the unit’s’ trip point
output (available on pins 13 and 14 of the I/O connector) for further process control.
To change the action of a trip point, refer to How to Select the Trip Point Action, page 455.
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