Watlow 8LS Controller Manual do Utilizador descarregar pdf (Página 76)

68 8LS User’s Guide

Setup

Alarm Types

Global Alarms

Global alarms occur when a loop alarm, set to Alarm, is

unacknowledged, or when there are any unacknowledged failed sensor

alarms. (If an alarm occurs, the 8LS front panel displays an appropriate

alarm code). Even if the alarm condition goes away, the global alarm

stays on until you use the

Alarm Ack

key (or ANASOFT) to

acknowledge it.

Process Alarms

Process alarms include high and low deviation and high and low process

alarms. You can set each of these alarms to Off (no alarm function) or

On (Standard alarm function).

•

High process and high deviation alarms activate when the process

variable goes above a value you set. They remain active until the

process variable goes below that value minus the deadband. (See

diagram below.)

•

If you don’t use a digital output for PID control, you can assign it to

one or more process variable alarms. The output is active if any of

its alarms are active. All alarm outputs are active Low or active

High, depending on the global alarm output polarity setting.

•

Low process and low deviation alarms activate when the process

variable goes below a value you set. They remain active until the

process variable goes above that value plus the deadband. (The dia-

gram below shows these alarms.)

When the controller powers up or the setpoint changes, deviation alarms

do not activate until the process goes inside the deviation alarm band--

preventing deviation alarms during a cold start. (High and low process

alarms are always enabled.)

h Alarm Limit

Setpoint

Low Alarm Limit

SP + Deviation

SP - Deviation

}

Deadband

}

Deadband

}

Deadband

}

Deadband

h deviation alarm on

h deviation alarm off

Low deviation alarm on

Low deviation alarm off

h process alarm off

h process alarm on

Low process alarm on

Low process alarm off

1 2 ... 71 72 73 74 75 76 77 78 79 80 81 ... 139 140

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