Dependence between switch threshold and
hysteresis on
MIN / MIN- (minimum safety) and
MAX / MAX- (maximum safety):
On minimum safety a set point infringement remains active as
long as the measured signal is smaller than the switch
threshold plus hysteresis (
SETP + HYST), on maximum safety
the value of the switch threshold minus hysteresis (
SETP -
HYST).
On settings
MIN and MAX in addition to the alarm condition the
relay also de-actives on a fault condition (
ALARM).
Connection between switch threshold and reset threshold
on
TRD / TRD- (trend monitor):
The trend feature has the task of monitoring the change of the
input signal over a specific time span. The time base over
which the signal is to be monitored can be set up in menu
group
PARAM address TRDT. The calculation is the difference
between the start value MW
A
and the end value MW
E
of the
interval. If the calculated value is larger than the value set up
in
SETP then the relay is deactivated. The relay is powered up
again once the value has dropped below that set up in
RESP.
The direction of the difference (rising or falling) is set up by
the prefix. A new value is calculated every second (moving
interval).
Relay deactivated (no power), yellow LED off
Measurement value
Relay deactivated (no power), yellow LED
HYST
SETP
MIN
HYST
SETP
Measurement Measurement
MIN
Process transmitter
57
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