Page 62
Sonic-Pro
Industries, Ltd.
Industries, Ltd.
ProSeries
by Blue-White Ind.
TM
When a process control relay channel is configured to monitor Flow Rate, it can be used
to indicate that the rate of fluid flow has reached or passed configured trigger values. A
Process Control Screen for a channel configured in this way is shown at right. The
RELAY
soft button is used to visit each relay channel in turn and go back to the Run
Mode screen. The
CLEAR
soft button can be used to clear an alarm condition while the
problem causing the alarm is being rectified.
Operation of Flow Rate Alarms will be described with reference to the state diagram
below.
8.3
Flow Rate
Alarms
The relay channel starts in the
CLEAR
s
tate. It will remain in this state so long as
the displayed flow rate remains
both
less
than the
High Trigger
value and greater
than the
Low Trigger
value. Note that the
displayed flow rate is subject to the
configured averaging, high and low flow
cutoff and any scaling offset value.
If the flow rate rises to or above the
High
Trigger
value or falls to or below the
Low
Trigger
value, then the relay channel
changes to the
ALARMING
state (arrow a
in the diagram at right). If the
Alarm
Delay Time
has not been configured or it
has been configured to zero, the relay
channel immediately changes to the
ALARMED
state (arrow b). Otherwise, it
remains in the
ALARMING
state while the
Alarm Delay Time
is counted down. In
this state, the relay is not energized. The status displays as Status:
ALARMING
in
alternating black-on white and white-on-black and the
CLEAR
soft button is present. If
the
CLEAR
soft button is pressed, counting down the
Alarm Delay Time
restarts. This
state gives an operator time to correct the condition causing the alarm or for the
condition to correct itself if it is transient.
When the
Alarm Delay Time
expires in the
ALARMING
state (which may be
immediate, see above) the relay channel changes to the
ALARMED
state (arrow b). The
relay is energized. The status displays as
Status:
ALARMED
in white-on-black. The
CLEAR
soft button is present. If the
CLEAR
soft button is pressed in the
ALARMED
state and a non-zero
Alarm Delay Time
is configured, the relay channel changes to the
CLEARING
state (arrow c). The relay is now de-energized. The status displays as
Status: CLEARING
in white-on-black and the
CLEAR
soft button is not present. The
purpose of this state is similar to the
ALARMING
state, but it is available after the
alarm has occurred if the operator did not act early enough. The flowmeter counts down
the
Alarm Delay Time
. If this time expires and the condition causing the alarm has not
been removed (arrow e, see below), the relay channel returns to the
ALARMED
state
(arrow d). If the
CLEAR
soft button is pressed in the
ALARMED
state but
Alarm
Delay Time
is zero or has not been configured, then nothing will happen unless a
Release value
has not been configured and the flow rate has returned to normal (more
on this below). In this case, the relay channel changes to the
CLEAR
state (arrow e).
In the
ALARMING, ALARMED
and
CLEARING
states, the relay channel may change
to the
CLEAR
state (arrow e) without user action if a
Release
value has been
configured for the
Trigger
value that has been passed to cause the alarm and the flow
changes to be equal to or inside that release value. For example, if the alarm occurred
because the flow rose above the
High Trigger
value and a
High Release
value has
8.3.1
Basic
operation
