We have put in some special features for this particular task. When the pressure switch function is selected, the calibrator goes into a special high speed sampling mode on the pressure channel. That allows it to grab an accurate value when it detects the switch state change.
And, it automatically detects the change of state by monitoring the voltage drop across the switch contacts. This needs to be done with either dry contacts or a connected DC voltage of 30 volts or less.
Once the switch has been connected (see illustration above), push the “PUMP” button to begin increasing pressure to the switch. When the switch changes state, the display will change from OPEN to CLOSED or vice versa (depending on the original state of the switch).
Then, use the variable vent valve on the side of the calibrator to slowly reduce the pressure until the display shows the switch state changed back to its original status (OPEN or CLOSED).
The display will now switch to show the data when the switch opened (display reads “SWITCH OPENED AT”). By pressing F2-NEXT, you can step through the displays to see the values where the switch reclosed and what the difference (deadband) is between the 2 values.
A recommended practice is to take the first pass to get a rough idea of the actual setpoint of the switch. Then, on a subsequent pass, stop the pump just before the setpoint and use the vernier control to approach the setpoint very slowly. This will allow you to get the most accurate value possible.
Of course, there are variations on this depending upon whether you need to get the setpoint for an increasing value or decreasing value and whether the switch is normally open with no pressure or normally closed.
Either way, the BetaGauge calibrators offer an easy and accurate way to test pressure switches.