The [TRIP POINTS] Key
Chapter Four: Functional Overview
58
Channel Selection
Each trip point must be assigned to a channel. If you are using a single pressure transducer, set
the trip point channel to Channel 1. If you are using a 274 multiplexer, the trip point channels
assigned may differ from the active channel.
TP A Channel
#1
TP B Channel
#1
Use the Adjust knob to select the channel (1 through 3) for each trip point. Press the an arrow
key to move to the other trip point field.
Note
The Adjust knob scrolls through Channels 2 and 3 even when the 670
instrument is not connected to a 274 multiplexer. This enables you to
configure the 670 instrument in one location and then insert it into a
system with a 274 multiplexer, without modification.
Latching a Trip Point
The 670 instrument provides the ability to “latch” the trip points. Once the latch on a trip point
is enabled, the next time the trip point value is crossed (either the pressure exceeds the high trip
point, or drops below the low trip point) the relay will remain in that state as long as the latch is
enabled, regardless of the pressure value. The trip point relay will return to its normal state only
when the latch is either cleared or disabled, and the pressure value falls within the normal limits
defined by the trip points. Pins on the I/O connector allow you to use an external signal to
release the relay, yet maintain the latched mode. The next time that the trip point value is
crossed, the relay will become latched again. Refer to How To Clear a Latched Trip Point, page
77. The latch feature is useful if you need to implement a manual acknowledgment of an alarm
condition.
Note
If the 670 instrument is connected to a 274 multiplexer, you must use the
Y-cable, CB670-2, to access the trip point latch pins. Refer to
Appendix D: Interface Cables for a Type 274 Multiplexer, page 145, for
the pin assignments.
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