80-4280-10, Rev. 4
CONFIGURATION / CALIBRATION
32
LOSS OF
DEMAND
SIGNAL (LOS)
The DCM-2 is capable of determining if the
Demand input signal to the actuator is outside
of an acceptable range. The DCM-2 uses a
configurable loss of signal (LOS) threshold to
determine if the Demand signal falls below a
minimum value. Unless otherwise specified in
the original order, the factory set threshold is 3.2
mA. When the DCM-2 senses a LOS condition,
it will provide a system alarm, and illuminate the
“DEMAND” LED. The actuator will also respond
in a predetermined manner.
The DCM-2 can be configured for two LOS
actions:
1.
Stay in Place
– the actuator output shaft stays
in place until the Demand signal returns to the
acceptable range. This is the factory default.
2.
Go-to-Position
– the actuator output shaft
will move to a preset position, designated in
percentage of travel. For example, if the LOS
action is set for GTP 50%, the actuator output
shaft will actuator to the 12 mA position (based on
a 4-20 mA span).
The LOS parameters can be configured using
HART or SERIAL commands.
CAUTION
The following procedures could
cause the actuator to reposition,
which can adversely affect the
process and cause potentially
dangerous conditions.
HART
method
HART DD Menu Location: MENU 5C
Functions> Configuration> Demand Setup
Command: LOS Mode
Selections:
Stay
- select if the actuator should hold output
shaft position when a loss of signal occurs.
Go-to-pos
- select if the output shaft should go to
a specific position when a loss of signal condition
occurs. Configure the position with LOS Pos.
Command: LOS Pos
Enter the desired output shaft postition the
actuator will achieve upon loss of Demand signal.
This value is entered as a percentage of full travel.
Command LOS Mode must be set to “Go-to-Pos”
to use this feature.
Command: DemLimLwr
Enter the decimal value of the lower threshold for
detecting a loss of control signal. (typically 3.2 mA
for a 4-20 mA application.)
SERIAL
command method
Command: demlos
Arguments:
###
: Enter the desired mode or
lower Demand threshold as follows:
sip
: select if the actuator should hold its current
position when a loss of signal condition occurs.
gtp
: select if the actuator should go to a specific
position when a loss of signal condition occurs.
Configure the position with the demlosgtp serial
command.
(e.g.: “demlos sip” will cause the actuator to hold
position during a loss of signal condition)
OR
n:
Where n is a decimal value of the lower threshold
for detecting a loss of control signal.
(e.g.: “demlos 3.2” sets the lower LOS threshold
to 3.2 mA)
Command: demlosgtp
Arguments:
###
: Enter the desired loss of signal
position as a percentage of actuator travel span.
(e.g.: “demlosgtp 50” will position the actuator to
50% when a loss of signal condition occurs and
the demlos command is set to gtp.)
