Application Note

2 Fluke Corporation Calibrating pressure switches with a DPC
Next set up a test for this pres-
sure switch in which you want
the following performance:
•
Setpoint variation of +/- 1.0 psi
• Deadband minimum 1.5 and
maximum 2.5 psi
Now you’re ready to make con-
nections to the pressure switch
module. Be sure to:
• Take proper precautions—
disconnect the device from
the process it controls (both
the electrical and pneumatic
connections)
• Connect the center terminals
of the DPC across the output
contacts of the switch
• Connect a pump to the pneu-
matic input of the switch
with a tee connection into
the pressure module, like the
Fluke-700 Series pictured in
Figure 1.
When all connections are
complete it should resemble
Figure 1.
Setting up the DPC
To set up the DPC, first con-
nect the pressure module. In the
measure screen, select mea-
sure continuity/ohms. Toggle
to the source screen with the
MEASURE/SOURCE button. Select
pressure. Once the pressure
module has initialized, make sure
the pressure module is vented
to atmosphere and select the
CLEAR/ZERO button to zero out
the offset of the pressure module.
Advance to the split screen
by depressing the MEASURE/
SOURCE button. Select the AS
FOUND softkey and select single
point
switch test. From there we
will, configure the test per these
parameters:
Setpoint: 12 psi
Setpoint type: The contacts need
to be closed to actuate the relief
valve above 12 psi; in other
words, the action happens when
the pressure is high; this is a
“high” type setpoint.
Set state: When the switch is
closed a relief valve is actuated;
the set state is “short.”
Tolerance: 1.0 psi
Deadband min: 1.5 psi
Deadband max: 2.5 psi
Trip function: Trip continuity
Depress the enter key and
enter the setpoint value (Figure 2)
and depress enter. Configure the
SETPOINT TYPE and SET STATE
as shown, then fill in the test
template as per Figure 3. Depress
Done.
Performing the switch
test
The test can now be performed
by selecting the MANUAL TEST
softkey (Figure 4). Using the hand
pump connected (Figure 1), vary
the pressure applied to the pres-
sure switch and pressure module
slowly, back and forth across the
setpoint and reset points. It will
be apparent that the set/reset
has changed as indicated by the
status in the measure screen. As
the state changes, the actual set
and reset points will be logged
during the test (Figure 5). When
the set and reset states are cap-
tured (it is a good idea to repeat
the testing of set and reset several
times to confirm repeatability),
depress the DONE softkey.
Figure 6 shows the AS FOUND
test result. Note that the DEAD-
BAND ERROR is indicated in
reversed type. If the AS FOUND
setpoint was greater than 1 psi
Figure 1.
754
DOCUMENTING PROCESS CALIBRATOR
Hand Pump
Pressure
Module
Figure 2.
Figure 3.
Figure 4.
Figure 5.