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Model 289A Differential Pressure Indicating Switch
Section 3
itself. For example, the high switch (right side of scale) may be set at
full scale, but should not be set near zero. The low switch may be set at
zero, but should not be set near full scale. (Observe deadband values for
specific models).
3. If switch performance is unsatisfactory (set point does not repeat, dead-
band is excessive, pointer exhibits hysteresis, contacts are unstable, etc.),
remove the scale and inspect the switch and the switch mechanism. The
scale is split to allow for removal without pulling the pointer.
Changing Set Point of an In-Service Instrument (Not Recommended for
Nuclear Qualified Units)
Use the following procedure to set a set point for an instrument that is in ser-
vice, when calibration pressures cannot be applied. See Figure 3.8 for specific
locations denoted by items A, B, C and D.
1. Remove the bezel/cover. Do not remove the pointer or scale.
2. Insert hex wrench in the switch adjust post.
3. Loosen the switch lock-screw, (item B), 1/2 to 1 turn.
4. With a hex wrench, move the index pointer (item C) to the new set point
as indicated on the switch index (item D).
5. If possible, check the set point by varying the process pressures and
observing the pointer readings when the switch actuates. (Open the mani-
fold bypass valve slowly and watch for “pointer-jump” at the set point or
by electrical signal.) Adjust the setting, if necessary, and repeat the test
several times to verify stability.
Figure 3.8—Set point adjustment
Содержание BARTON 289A
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