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Set Points & Adjustability

The adjustability statements in our literature are based upon setting the switch on increasing pressure.  The minimum set point capability is based upon 3 factors.

  1. Mechanical limitation of the adjustment
  2. The minimum DP the switch can be set and still clear when the  DP returns to 0 (Hysteresis issue)
  3. The minimum DP set point  value for where the switch does not deactivate during over-range of the switch.

The maximum value of these 3 conditions, determines the minimum defined set point. While it may be possible to set the switch below or above the defined set points, it is advisable for the customer to make sure the switch clears  on return to 0 DP and verify that the switch does not deactivate during over-range (recommend 120% of FSR).

Mid-West Instrument can pre-set any switch free of charge.  The customer need only specify whether to set on increasing differential pressure or decreasing differential pressure.  If neither is stated we assume the set point will be set on increasing differential pressure.

We set our switches using the calibration standard that we calibrate our product to.  The switch set point accuracies are equal to the defined accuracy of the gauge.

Customer Switch Setting:

If the customer needs to set a switch, the following general methods can be used.  The most accurate method to set a switch is to use an external reference standard. If a reference standard is not available and the gauge has an indicating display, the display can be used to set the switch.

Equipment required:  Pressure Source, Multi-meter / Resistive Buzzer Box, Reference gauge (optional)

NOTE:  The Model 120 series of gauges have a small amount of leakage from Hi to Low (Piston style).  A hand pump style calibrator is not sufficient.
NOTE:  Low side port can be left open to atmosphere while performing the set point adjust.

To set on increasing:

  1. Increase your pressure to the desired set point. (Hold that pressure)
  2. Increase the switch set point above the desired switch set (switch deactivated).
  3. Slowly decrease the switch set point until the contact activates.
  4. Decrease pressure to 0
  5. Slowly increase pressure and confirm set point

To set on decreasing:

  1. Increase your pressure to the desired set point. (Hold that Pressure)
  2. Adjust the switch set point below the desired switch set (switch activated).
  3. Slowly increase the switch set point until the contact de-activates.
  4. Decrease pressure until the switch activates.
  5. Slowly decrease pressure and confirm set point
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