Vaisala PTU300 User's Guide download pdf (Page 122)

USER'S GUIDE____________________________________________________________________

120 _________________________________________________________________ M210796EN-E

Mode 4 is usually used if an alarm needs to be triggered when the

measured value exceeds a safe range. The relay is active when

measurement is in range, and is released if the value goes out of range or

the measurement fails.

NOTE

If the measurement of the selected quantity fails or the transmitter loses

its power, the relay is released.

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 60 %RH and the hysteresis value is 5

%RH, relay activates when the relative humidity reaches 60 %RH. As the

humidity decreases, relay releases at 55 %RH.

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)

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Vaisala PTU300 User's Guide Page 122