ABB AMTD-1 P Assembly And Operating Instructions Manual page 16

Digital instruments
2. AMTD-1-R P / AMTD-2-R P / VLMD-R P functions
EN
Maximum and minimum relay operation
When the measurement exceeds the threshold value, the relay changes state
and the alarm is tripped after a programmable delay dLY, which appears on
the display alternately with the normal instantaneous measurement.
ALL [ALarm Low] indicates that the minimum threshold has been exceeded
ALH [ALarm High] indicate that the maximum threshold has been exceeded
Even in alarm conditions, pressing the button briefly enables you to view
the minimum and maximum values.
The alarm stops when the measurement returns within the threshold in-
cluding the value of the hysteresis.
Alarm enabling logic
The output from the relay is an open contact type. You can program the
configuration of the relay:
n0 [normally Open] the contact is open when the relay is not energized.
nC [normally Closed] the contact is closed when the relay is not energized.
State of device
Not powered
Powered, alarm not on
Powered, alarm on
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nO (default) Positive safety nC