19
Model 764 Differential Pressure Transmitter
Section 3
Initial Calibration Adjustments
If a transmitter is installed after an extended period of storage, a calibration
test should be performed before operating the transmitter to ensure correct
performance.
Accuracy of the test equipment used for the calibration test should be ap
-
proximately four times the accuracy of the instrument under test. See Table
4.1,
page 23
, for general requirements.
Calibration Check
The transmitter should be tested at minimum, maximum and 50% calibrated
range pressures for at least three cycles. See Table 3.1—Calibration Check
-
points,
page 20,
for recommended transmitter output values and the associ
-
ated tolerances, in current and voltage, for 4-20 mA and 10-50 mA outputs.
To test the transmitter calibration, perform the following steps:
1. Remove the calibration access plugs from the transmitter cover using a
socket or a wrench.
IMPORTANT: If there are no calibration access plugs in the cover, the cover must be
removed to adjust calibration. See Transmitter Cover Removal,
page
25
, for instructions.
2. Connect the electrical readout device to the transmitter as shown in Fig
-
ure 3.3 for either current or voltage readout. If the transmitter is equipped
with an EGS Quick Disconnect connector assembly, secure the two
mating connectors with the bayonet ring (see Figure 4.1,
page 26,
for
details).
3.
With minimum calibration pressure applied, compare the output signal to
the recommended value in Table 3.1, and adjust the zero control potenti
-
ometer in the compensating direction as required.
4.
Apply calibration pressure corresponding to maximum output, compare
the output signal to the recommended value in Table 3.1, and adjust the
span control potentiometer in the compensating direction as required.
5.
Repeat steps 3 and 4 as necessary to obtain desired accuracy. (Zero and
span controls have a minimum of interaction when adjusted, so this step
may or may not be required.)
6.
Apply 50% calibration pressure and verify that the output is within Table
3.1 specifications. If it is not within recommended specifications,
recalibrate the transmitter using the calibration procedure on
page 23
or return the transmitter to the factory.
