ATC770 Microprocessor-Based Pressure/Process Controller 37
Normally Closed Contact are held OPEN, while the Normally Open contacts are held CLOSED. On
power failure, they are released.
On start-up, a Low Alarm may cause the unit to go into an undesired alarm condition prior to
reaching running conditions. This Alarm can be masked so that the Low Alarm will be deactivated
until it has gone above the alarm value for the first time. It will then operate as a normal low alarm.
The default values for Alarm 1 are: an inhibited low alarm set at 5% of full scale, linked to the
primary process input, 0.4 second filtering, 1% hysteresis, automatic reset and failsafe mode. Each
alarm may be set to 110% of full scale.
The default values for Alarm 2 are: high alarm at 60% of full scale, linked to the primary process
input, 0.4 second filtering, 1% hysteresis, automatic reset, and failsafe mode.
The default values for Alarm 3 are: high alarm at 80% of full scale, linked to the primary process
input, 0.4 second filtering, 1% hysteresis, automatic reset, and failsafe mode.
Set the Alarm parameters before setting the alarm value. If the alarm parameters have already been
set, set the alarm values as described in Section 6.2.7.
6.2.1 SETTING WHAT THE ALARM WILL MONITOR (ALARM INPUT CHANNEL LINK)
The Alarm 1 Input Channel Link defaults to the primary process input. To check or change this value
press the FUNC key until
nonE
and
GROUP
show on the display. Press the ▲ key until
3
shows in
the upper display. Press the FUNC key until
A1.LNK
shows in the lower display. Select the choice
desired by pressing the ▼ or ▲ keys. The choices are:
OFF
, (disabled), a process alarm (on achieving
a specific pressure)
Proc
, a band alarm around a specific pressure range
bAnd
, or a deviation alarm
from a specific pressure
dEu
. Press the FUNC key to lock in the value and advance to the next
parameter. Similarly, you may configure Alarm 2
(A2.LNK)
and Alarm 3
(A3.LNK)
.
6.2.2 SETTING ALARM TYPE
A high alarm will activate when a set point is exceeded. A low alarm will activate whenever the
value falls below a set point (including startup). An inhibited low alarm must exceed the low alarm
set point before it is enabled. Then it will work like a low alarm. This is ideal on startup.
The default alarm type for Alarm 1 is high. To check or change this value press the FUNC key until
nonE
and
GROUP
show on the display. Press the ▲ key until
3
shows in the upper display. Press the
FUNC key until
A1.TYP
shows in the lower display. Using the ▼ or ▲ keys, select
HI
for high level
alarm,
LO
for low level alarm or
Inhib
for a low level alarm with mask at start-up. Press the FUNC
key to lock in the value and advance to the next parameter. If finished, press A/M to return to the
operating screen. Similarly, you may configure Alarm 2
(A2.TYP)
and Alarm 3
(A3.TYP)
.
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