18
Section 4
Model 753A Gage Pressure Transmitter
loop resistance values for various cable wire sizes.
4.
Install a load resistor sized for the application.
!
WARNING: Failure to properly calculate power supply DC output voltage
may result in inaccurate transmitter readings, possibly leading to safety
system performance degradation during design basis events. To avoid
equipment inaccuracy hazards, follow the examples and tables in this
section for determining the proper power supply DC output voltage.
Calibration Checkpoints
Table 4.2 presents the transmitter output values in current and voltage, along
with the associated tolerance for instrument with 0.5% accuracy, for both the
4-20 mA and 10-50 mA variations. Instruments are held to the same toler-
ances during factory calibration. For calibrating instruments with 0.25%
accuracy, divide the tolerances shown by one-half.
Table 4.2—Calibration Checkpoints for Instrument with 0.5% Accuracy
Applied Calibration
Pressure Checkpoint
(% of Span)
Output*
4-20 mA Transmitter**
10-50 mA Transmitter***
Current
(±0.08 mA)
Voltage
(±0.04 Vdc)
Current
(±0.2 mA)
Voltage
(±0.04 Vdc)
0%
4 mA
2 Vdc
10 mA
2 Vdc
25%
8 mA
4 Vdc
20 mA
4 Vdc
50%
12 mA
6 Vdc
30 mA
6 Vdc
75%
16 mA
8 Vdc
40 mA
8 Vdc
100%
20 mA
10 Vdc
50 mA
10 Vdc
*This value includes the effects of conformance (non-linearity), deadband, hysteresis, and repeatability.
**This value was obtained using a 500-ohms load resistor.
***This value was obtained using a 200-ohms load resistor.
Calibration Procedure
The following procedure can be used to obtain "as found" calibration values
or perform a full calibration.
•
To obtain the “as found” calibration values (calibration check only),
perform steps 1 through 6 and steps 10 through 12,
skipping steps 7
through 9
.
•
For periodic calibration or in cases where the “as found” calibration
values do not meet the tolerances specified in Table 4.2,
perform all
12 steps
.
1. Verify that the transmitter is installed in accordance with the mounting
guidelines on
page 10
and the piping guidelines on
page 11
.
2.
Locate the block valve and make sure it is closed. The block valve is nor
-
mally installed at the facility to isolate the process being monitored from
