Vaisala DMT340 - Manual (Page 132)

User's Guide _______________________________________________________________________
130 __________________________________________________________________ M210704EN-G
Hysteresis
Hysteresis function is to prevent the relay switching back and forth when
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 released
only until 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 -30 ºC and the hysteresis value
is 2 ºC, relay activates when the dewpoint reaches -30 ºC. As the
dewpoint then decreases, relay releases at -32 ºC.
>rsel tdf t
Rel1 Tdf above: - ? -30
Rel1 Tdf below: -30.00 'C ? -
Rel1 Tdf hyst : 5.00 'C ? 2
Rel1 Tdf enabl: ON ?
Rel2 T above: 30.00 'C ?
Rel2 T below: 20.00 'C ?
Rel2 T hyst : 1.00 'C ?
Rel2 T enabl: 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)