Halma ALICAT BC Series, Operating Manual

Page: 12 / 31

12 Control
Value Notes
a The analog input is used as the setpoint source. Digital setpoint commands are not
accepted.
s
Saved digital. Digital setpoint commands are accepted; the most recent command
will be used when the instrument is powered up. The analog input is disconnected
from the setpoint.
CAUTION: If the setpoint is consistently changed more often than every few
minutes, the nonvolatile memory may be damaged and may no longer correctly
store the setpoint.
u Unsaved digital. Setpoint changes from the digital setpoint commands are accepted
but will not affect the setpoint used by the instrument on the next power up. The
analog input is disconnected from the setpoint.
This setting is recommended when the setpoint will often be changed more often
than every few minutes.
Example: aLSS a

(the analog input will be the source for the setpoint for
instrument A)
Maximum Setpoint Ramp Rate
This value determines the maximum rate at which the setpoint can change (controllers
only). It applies to both increasing and decreasing setpoints, whether the setpoint was given
digitally or via the analog input.
To read the current setpoint ramp rate : unit_id SR

To set a new setpoint ramp rate : unit_id SR max_ramp_rate time_units

max_ramp_rate is the new maximum setpoint ramp rate. The value is a non-negative floating-
point value in the default units of the loop control variable (see page 13 ). The instrument
will use the closest available ramp rate.
time_units are the units for the ramp rate, per the table below:
Unit Label Values Notes
ms 3 millisecond
s 4 second
m 5 minute
Example: aSR 600 3

(set the maximum ramp rate to 600 [flow units] /ms for
instrument A)
To disable any limiting of the setpoint ramp rate : unit_id SR 0

Communication Watchdog
A communication watchdog (controllers only) will force a zero setpoint and close the controller
valve if no serial communication is received within a user-defined time period.

Note: The Communication Watchdog is only available when the setpoint is being set via
MODBUS communication and the Setpoint Source is set to "unsaved digital" (see page 11 ).
All other setpoint sources (ASCII, saved digital, analog) are not impacted by the
Communication Watchdog.
To read the current watchdog : unit_id WD

Example: aWD

(read watchdog time on instrument A)
To set a new watchdog : unit_id WD watchdog_time

watchdog_time is the desired watchdog duration, from 0–5000 milliseconds.