The [TRIP POINTS] Key
Chapter Four: Functional Overview
54
The [TRIP POINTS] Key
Use the [
TRIP POINTS
] key to configure the two trip points. Each trip point is defined by a
high and low setting and controls a relay. In addition, you choose the initial state of the trip
point relays; either energized or de-energized, and the trip point channel.
The 670 instrument contains two trip points; Trip Point A and Trip Point B. You set the high
value, the low value, and the hysteresis for each trip point. The trip point entries define a
“normal” operating range for the pressure signal. When the pressure signal deviates from this
normal range, the relay changes state to indicate an alarm condition.
If the 670 instrument is connected to a 274 multiplexer, you must use the Y-cable, CB670-2, to
access the trip point pins available on the I/O connector. Refer to Appendix D: Interface Cables
for a Type 274 Multiplexer, page 145, for the pin assignments.
Trip Point Settings
The trip points can be set to any pressure within ±105% of transducer full scale. If you prefer to
use a single pressure threshold as the alarm limit, disable one of the trip points. To disable a
high trip point, select a pressure equal to or greater than +105% of full scale. To disable a low
trip point, select a pressure equal to or less than -105% of full scale.
Table 15 summarizes the action of a trip point based on the pressure reading of the selected trip
point channel.
Action of the Trip Points
Pressure Value on the Trip Point Channel
Action
> trip point high value plus hysteresis value
Trip point relay is activated
Equal to or between the trip point high and trip point
low values
Trip point relay is not activated
< trip point low value minus hysteresis value
Trip point relay is activated
Table 15: Action of the Trip Points
The trip point settings screens define the high and low settings for Trip Point A (TP A). The
[
CURSOR
] key moves the cursor from left to right on the line, so you can change the trip point
value. From the TP A HIGH screen press the down arrow key [
] moves the cursor to the
TP A LOW entry. Press the down arrow key [
] again to configure the high and low values
for Trip Point B.
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