Vaisala DRYCAP DMT340 SERIES Guia do Utilizador descarregar pdf (Página 121)

Chapter 4 ________________________________________________________________ Operation

VAISALA ______________________________________________________________________ 121

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

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.

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Vaisala DRYCAP DMT340 SERIES Guia do Utilizador Página 121