Process Indicator Zero-And-Span Calibration - Emerson Fisher 4194HA Instruction Manual

4194HA, HB, HC Controllers
July 2018
If the prestartup checks or startup reveal faulty controller operation, perform the calibration described in this section.
These instructions are valid for either shop or field calibration, if open process loop conditions exist.
Unless otherwise noted, key numbers refer to figure 6‐1.
Process Indicator Zero‐and‐Span Calibration
Provide a regulated process differential pressure to the differential pressure unit. Also, plug the controller output
connection and provide a regulated supply pressure to the controller. Do not exceed the normal operating pressure in
table 1‐4.
Refer to figure 3‐1 for location of adjustments.
Note
Any adjustment of the process indicator span adjustment screw requires readjustment of the process indicator zero adjustment
screw.
1. Remove the two machine screws (key 6) and lift off the proportional band indicator cover (key 36).
2. Set the proportional band adjustment between DIRECT and REVERSE.
3. Adjust the process differential pressure until the input to the differential pressure unit is equal to the lowest limit of
the scale range.
4. If necessary, adjust the process indicator to the lowest limit of the process scale by loosening the zero adjustment
locking screw and turning the zero adjustment screw.
5. Adjust the process differential pressure until the input to the differential pressure unit is equal to the highest limit of
the scale range.
6. Note whether the process indicator is above or below the upper limit of the process scale.
7. Adjust the process indicator span adjustment screw as follows: Clockwise to increase the span for a low indication;
counterclockwise to decrease the span for a high indication. Adjust the span adjustment screw to correct for
approximately one‐half the error.
8. Repeat steps 3 through 7 until the error is eliminated.
9. Adjust the process differential pressure until the input to the differential pressure unit is equal to 50 percent of the
process scale range. The process indicator should point to the 50 percent process scale mark within ±2 percent of
span.
D If the error is greater than ±2 percent, perform the appropriate maintenance calibration procedure in the
Maintenance section.
D If the error is less than ±2 percent but more than ±1 percent, proceed with step 10.
10. Adjust the process indicator to within ±1 percent of the 50 percent scale mark by loosening the zero adjustment
locking screw and turning the zero adjustment screw. This distributes the error over the entire scale range and
brings all points within ±1 percent of the process input span.
11. Adjust the process differential pressure to 0 percent of the scale range.
12. The process indicator should indicate a zero scale reading, ±1 percent of the scale span.
13. Adjust the process differential pressure to 100 percent of the scale range.
14. The process indicator should point to the full scale reading, ±1 percent of the process scale span.
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Instruction Manual
D200156X012