12
9. Apply 0%, 25%, 50%, 75%, 100%, 75%, 50%, 25%, and 0% of full-scale
differential pressure consecutively to instrument without overshoot. Lightly
tap indicator to overcome friction. Pointer should accurately indicate each
applied pressure.
10. Set stops to prevent pointer from striking snubbers on scale. Test setting by
moving pointer from zero position to 50% position manually and then letting
pointer return freely. If necessary, tap pointer hub to tighten it to shaft.
3-7. Changing Switch Setpoint
(Tools: Screwdriver, 1/8 Hex Allen wrench) (See Warning on pg. 9)
Setpoint
— The measured pressure at which the snap-switch actuates and thereby
changes the states of the N.O and N.C. contacts. For example, the setpoint of the
low switch is 24 psid with decreasing pressure.
Deadband
— The difference in the measured pressures between switch-actuation
and switch-reset. Deadband is
usually expressed as percent-
age of full scale (% of F.S.).
Deadband is not adjustable.
For example, the switch above
was found to reset at 26.4 psid
with increasing pressure. The
deadband was 2.4 psi, or 4% of
the full scale (0 to 60 psid).
A. In-Service Instruments
(calibration pressures
cannot be applied)
1. Remove bezel.
Do
not remove pointer or
scale.
2. Insert hex wrench in
switch adjust post,
(item A, Fig. 3-4).
3. Loosen switch lock-
screw, (item B), 1/2 to
1 turn.
4. With hex wrench,
move index pointer
(item C) to new set-
point as indicated on switch index (item D).
5. If possible, check setpoint by varying process pressures and observing
pointer readings when switch actuates. (Open manifold bypass valve
slowly and watch for “pointer-jump” at setpoint or by electrical signal.)
Adjust setting if necessary, repeat test several times to verify stability.
Note: Switch index has 10 divisions shown by tick marks in Figure 3-4. Positions 0,
5, and 10 are also labeled along the bottom of the index as well.
example
: Scale has range of 0-60 psid. Setpoint is 24 psid, with decreasing pres-
sure, (24/60 x 10 = 4).
figure 3-4.
Setpoint
adjustment
