Chapter 4 ________________________________________________________________ Operation
VAISALA_______________________________________________________________________ 95
Hysteresis
The hysteresis function prevents the relay switching back and forth
when the measured value is near to the setpoint values. The relay is
activated when the measured value passes the exact value of the
setpoint. When returning to and passing through the setpoint again, the
relay is not released before the value reaches the setpoint
increased/decreased by the hysteresis value, see Figure 39 on page 94.
The hysteresis should be sm
aller than the difference of the setpoints.
NOTE
If both setpoints are specified and the "above" setpoint is lower than
the "below" setpoint, the hysteresis works in the opposite direction,
that is, the relay is released when the measured value passes the exact
value of the setpoint.
Relay Indicating Barometer Error
Status
You can set a relay to follow the operation status of the device. By
selecting FAULT STATUS for output quantity a relay changes state
on the basis of the operation status as follows:
FAULT STATUS
Normal operation: relay active (C and NO outputs are closed)
Not measuring state (error state): relay released (C and NC outputs are
closed).
See Figure 40 below for an illustrative example of the FAULT
STATUS relay output mode.
1212-004
Figure 40 FAULT STATUS Relay Output Mode
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