Watlow Series SD31 PID with Optional Countdown Timer Instrukcja Użytkownika Pobierz pdf (Strona 59)

Alarm Hysteresis

An alarm state is triggered when the process value

reaches the alarm high or alarm low set point. Alarm

hysteresis defines how far the process must return into

the normal operating range before the alarm can be

cleared.

Alarm hysteresis is a zone inside each alarm set

point. This zone is defined by adding the hysteresis val-

ue to the alarm low set point or subtracting the hystere-

sis value from the alarm high set point.

View or change alarm hysteresis Alarm 1 or 2 Hys-

teresis, [hyS1] or [hyS2] (Setup Page).

Alarm Latching

A latched alarm will remain active after the alarm

condition has passed. To clear a latched alarm, press the

Infinity Key ˆ. It can only be deactivated by the user.

An alarm that is not latched (self-clearing) will deacti-

vate automatically when the alarm condition has

passed.

Turn alarm latching on or off with Alarm

1 or 2

Latching

[

LAt1] or

[

LAt2] (Setup Page).

Alarm Silencing

Alarm silencing has two uses:

1. It is often used to allow a system to warm up after

it has been started up. With alarm silencing on, an

alarm is not triggered when the process tempera-

ture is initially lower than the alarm low set point.

The process temperature has to enter the normal

operating range beyond the hysteresis zone to acti-

vate the alarm function.

2. Alarm silencing also allows the operator to disable

the alarm output while the controller is in an alarm

state. The process temperature has to enter the nor-

mal operating range beyond the hysteresis zone to

activate the alarm output function.

If the Series SD31 has an output that is functioning as

a deviation alarm, the alarm is blocked when the set

point is changed, until the process value re-enters the

normal operating range.

Turn alarm silencing on or off with Alarm 1

or 2

Si-

lencing [Sil1] or [Sil2] (Setup Page).

Retransmit

The retransmit feature allows a process output to

provide an analog signal that represents the set point or

actual process value. The signal may serve as a remote

set point for another controller or as an input for a chart

recorder to document system performance over time.

Any process output can be configured as a retransmit

output.

Normal Operating Range

Alarm

enabled

here

Alarm

triggered

here

Startup,

Alarm

disabled

Time

Temperature

Alarm High

Set Point

Alarm Low

Set Point

Process

Temperature

Hysteresis

Normal Operating Range

Alarm High

Set Point

Time

Temperature

Alarm Low

Set Point

The alarm state continues until the

temperature drops to the Alarm High

Set Point minus the hysteresis. A

latching alarm could be turned off by

the operator at this point. A non-

latching alarm would turn off

automatically.

The alarm state begins when the temperature

reaches the Alarm High Set Point

Process

Temperature

Alarm Hysteresis

Normal Operating Range

Low Side Alarm Range

High Side Alarm Range

Alarm High Set Point

Alarm Low Set Point

Time

empera

ure

Alarm Hysteresis

Watlow Series SD31 ■ 57 ■ Chapter 10 Features

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