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Model 752 and 752A Differential Pressure Transmitters
Section 4
Section 4—Calibration and Maintenance
General Field and Periodic Maintenance
Electronic Transmitter
The electronic transmitter circuits are basically maintenance-free and do not
require routine preventative maintenance other than a periodic check of cali-
bration. See Calibration below for details.
Differential Pressure Unit (DPU)
The field maintenance schedule for the DPU will depend on the purpose for
which it is used. Periodic cleaning of the DPU is required if the instrument
is used in a system where solids or semi-solids can accumulate in the DPU
housings. Follow the guidelines in
DPU Inspection and Cleaning, page 22
, and
take the necessary safety precautions to avoid damage to the bellows.
Calibration
Each transmitter is calibrated at the factory prior to shipment. A 9-point cali-
bration check is recommended upon receipt, and again before the transmitter
is operated for the first time. If "as found" values are not within the specified
range, a full calibration should be performed.
The transmitter should be recalibrated at periodic intervals, determined
primarily by the usage of the transmitter, historical performance, the desired
accuracy of the output signal, or indications that the instrument may be out of
calibration. 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.
Test Equipment
To perform the calibration procedure for an instrument with 0.5% accuracy,
the test equipment should meet or exceed the requirements listed in
. For calibrating instruments, the pressure source should have at least 4
times the accuracy of the instrument being tested. In the event equipment is
substituted that does not meet these requirements, the accuracy of the recali-
brated transmitter must be derated accordingly.
