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How to Calibrate and Adjust the Differential Pressure Switch

Just like the pressure switch, the differential pressure switch can be calibrated to a known set point. You can calibrate the differential pressure switch as quickly as you can calibrate the pressure switch. However, in order to calibrate more accurately, some modifications have to been made to the process.


Quick calibration procedure of differential pressure switch

The required equipment includes:

(a) Variable pressure source

(b) Digital multimeter or continuity test lamp

(c) Tester

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Digital Electronic Differential Pressure Switches

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Calibration steps

Step 1

Connect a variable pressure source to the high side pressure port of the test gauge and the switch.

Step 2

Jumper the test lamp or multimeter (set to ohmmeter setting) C normal and no normally open

Step 3

Raise the pressure and record the test gauge reading when the circuit is closed.

Step 4

Slowly reduce the pressure and note the tester reading when the circuit is disconnected.

Step 5

Adjust the set point screw to increase or decrease the set point.

Step 6

Repeat steps 3, 4, and 5 until the contact changes at the desired increase or decrease in differential pressure set point.


Accurate calibration procedure

In order to calibrate the differential pressure switch accurately, we need to simulate the required service conditions.

The equipment required for this calibration process is:

(a) Differential pressure gauge (preferably digital)

(b) Variable pressure source

(c) Stop valve, drain valve and balance valve

(d) Continuity test lamp or digital multimeter

First determine that the set point occurs when the differential pressure increases or decreases, and then calibrate

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Use one of the following methods:

(a) Set point for increasing differential pressure

(b) Set point to reduce differential pressure


To calibrate the set point when the differential pressure increases:

Calibration steps

Step 1

Jumper the continuity test lamp or DMM to the c-common and no-normally open switch elements / contacts.

Step 2

Close the vent valve, open the balance valve, and increase the pressure on both sides of hi and lo to the static pressure that the differential pressure switch can see under normal operation conditions.

Step 3

When the static pressure is stable, close the balance valve to isolate the hi side from the lo side.

Step 4

Keep the high side pressure stable, slightly open the lo side vent valve to reduce the lo side pressure (increase the differential pressure) until the required differential pressure set point appears on the differential pressure gauge. Close the bleeder valve to stabilize the differential pressure. Check the status of the electrical contacts when possible and follow the instructions that match the status of the contacts:

(a) The set point is normal if:

Contact is made precisely at the increased differential pressure set point, repeat step

Verify 2- 4 as needed to verify calibration. Calibration complete.

(b) Contact open - set point too high

When the increased differential pressure is reached, if the contact is open, adjust the set point screw until the contact is closed. Repeat steps 2- 4

(c) Contact closed - set point too low

If the contact closes when the increased differential pressure is reached, adjust the set point screw until the contact breaks. From this point on, adjust the set point again until the contact is closed. Repeat steps 2-4


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To calibrate the set point for reducing the differential pressure:

Step 1

Connect a continuity test lamp or digital multimeter to the c-normal and no-normally open contacts.

Step 2

Close the vent valve, open the balance valve, and increase the pressure on both sides of HI and LO to the normal working static pressure.

Step 3

Close the balance valve to isolate the hi side from the lo side when the normal hi side pressure is stable.

Step 4

Slightly open the lo side drain valve to reduce the lo side pressure (increase the differential pressure) until the normal operating differential pressure appears on the differential pressure gauge. Close the drain valve to stabilize the differential pressure. When the normal working differential pressure is reached, the contact should be closed (closed). If the contact is still open under normal operating differential pressure, adjust the set screw until the contact is loose.

Step 5

Keep the high side pressure stable and slightly open the balance valve to increase the lo side pressure (decrease the differential pressure) until the required differential pressure set point appears on the differential pressure gauge.

Close the balance valve to stabilize the differential pressure. Check the state of the electric contact under the following differential pressure and operate according to the instructions matching the state of the contact:

(a) The set point is normal if:

The contact breaks precisely when the differential pressure setting is reduced, repeat step

Verify 2-5 as needed to verify calibration. Calibration complete.

(b) Contact open - set point too high

If the contact opens when the reduced differential pressure is reached, adjust the set point screw until the contact closes. From this point on, adjust the set point screw again until the contact opens. Repeat steps 2 -5

(c) Contact closed - set point too low

If the contact closes when the reduced differential pressure is reached, adjust the set point screw until the contact breaks. Repeat steps 2-5

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