Vaisala DMT346 - Manual (Page 125)

Chapter 4 _________________________________________________________________ Operation
VAISALA _______________________________________________________________________ 125
Hysteresis
Hysteresis function is to prevent the relay switching back and forth when
the measured value is near to the setpoint values.
Relay is activated when the measured value passes the exact value of the
setpoint. When returning and passing the setpoint again relay is not
released before the value reaches the setpoint increased/decreased by the
hysteresis value.
Hysteresis should be smaller than difference of the setpoints.
Example:
When the 'active above' value is 50 ºC and the hysteresis value is 2 ºC,
relay activates when the relative humidity reaches 50 ºC. As the humidity
then decreases, relay releases at 48 ºC.
>rsel tdf ts
Rel1 Tdf above: 0.00 'C ? 50
Rel1 Tdf below: 0.00 'C ? -
Rel1 Tdf hyst : 0.00 'C ? 2
Rel1 Tdf enabl: OFF ? on
Rel2 Ts above: 0.00 'C ? 80
Rel2 Ts below: 0.00 'C ? 60
Rel2 Ts hyst : 0.00 'C ? 1
Rel2 Ts enabl: OFF ? on
>
NOTE If both setpoints are specified and "above" setpoint is lower than
"below" setpoint, the hysteresis works in the opposite direction, that is,
relay is released when the measured value passes the exact value of the
setpoint.
Relay Indicating Transmitter Error Status
You can set a relay to follow the operation status of the device. By
selecting FAULT/ONLINE 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 or power off): relay released (C and NC
outputs are closed)