13
Move index pointer (item C) to division 4. Start from bottom of switch index (0
on low, 10 on high). Tighten switch lock (item B) snug plus 1/4 turn. Do not over-
tighten. This will place setpoint within ±2% of full scale.
B. Out-of-Service (Disconnected from process Setpoint Adjustment lines or
mounted on bench)
1. Drain and vent housings.
2. Attach calibration pressure source (air or N
2
) to HP housing.
3. Apply pressures and observe pointer readings for accuracy. Use a
pressure standard (Heise gage or equivalent) for reference. Change
pressures slowly in discrete steps. A “bleed-pressure” method may cause
errors.
4. Change switch setpoint as described in Part A, page 12.
5. Check setpoint by changing measured pressure to actuate switch. For
Example: To verify low-switch setpoint to 24 psid, apply approximately
30 psi. Then reduce pressure to approximately 25 psid, hold for a few
seconds, then continue in 1/4 psid steps until switch actuates. If setpoint
is incorrect, continue instructions in Part A.
6. To measure switch deadband, reduce pressure to zero, then increase
pressure until switch resets.
7. To verify repeatability of setpoint, repeat step 5 several times. For
improved accuracy, use smaller increments of pressure. Allow extra
time for slow response gages and for test systems that have long runs of
small bore tubing.
8. High alarm switches right side of the scale) are adjusted in a similar
manner. Apply increasing pressure to establish the switch setpoint,
decreasing pressure to measure deadband.
C. Notes
1. Always check setpoint after tightening switch lock screws.
2. Either switch may be set at any point of the scale, except allowance must
be made for deadband to enable switch to reset itself. For example, high
switch (right side of scale) may be set at 100% of F.S., but should not be
set near zero. Also, low switch may be set at zero, but not near full scale.
(Observe deadband values for specific models).
3. If switch performance is unsatisfactory (such as setpoint does not
repeat, deadband is excessive, pointer exhibits hysteresis, contacts are
unstable. etc.) remove scale and inspect switch and mechanism. Scale is
split for removal without pulling pointer.
a. SPDT: This is the standard model (low, high, or both).
b. DPDT: Two switches are stacked and actuated by a single lever (low,
high, or both).
c. Three (or four) SPDT: Switches have independent switch points.
Nos. 1 and 3 are usually low switches set for decreasing pressures.
Nos. 2 and 4 are usually set for increasing pressures.
d. Hermetically Sealed Switch (Micro 11HM41): this switch has wide
deadband, case is modified for electrical clearances, amperes are
reduced for 60 Hz service.
