"Pressure switch calibration" is a critical process to ensure the accurate operation of pressure switches in various industrial applications. These switches play a crucial role in monitoring and controlling pressure-related processes. Let’s dive into the procedure for calibrating pressure switches:

Pressure Switch Calibration Procedure

Understanding Pressure Switch Basics

Before we proceed with calibration, let’s review some essential terms related to pressure switches:

1. Set Point:
   • The pressure at which the switch changes state (opens or closes).
2. Normal State:
   • The switch state when at barometric pressure or the ideal state (either OPEN or CLOSED, depending on the switch type).
3. Reset Pressure:
   • The pressure at which the switch resets back to the normal state.
4. Tolerance:
   • The allowable variation from the set point pressure.
5. Repeatability:
   • The closeness of agreement between consecutive measurements.
6. Dead Band:
   • The pressure difference between the change-of-states (e.g., OPEN to CLOSE or CLOSE to OPEN).
7. Trip Type:
   • The direction in which the change-of-state occurs.
     • If the trip type is low, the change-of-state happens when the pressure is falling.
     • If the trip type is high, the change-of-state happens when the pressure is rising.

Calibration Steps:

1. Depressurize and Isolate:
   • Ensure the pressure switch is depressurized and isolated from the process.
2. Connect Pressure Source and Calibrator:
   • Connect the pressure source (preferably a hand pump) and the pressure calibrator (pressure gauge) to the pressure switch input.
3. Check Electrical Output:
   • Use a multimeter in continuity mode to verify the switch contacts:
     • For a normally open (NO) switch, check that the contacts are open.
     • For a normally closed (NC) switch, check that the contacts are closed.
4. Test Set Point:
   • Apply pressure to the switch until it changes state (e.g., from OPEN to CLOSE for an NO switch).
   • Record the pressure at which the switch changes state (set point).
5. Test Reset Pressure:
   • Release pressure until the switch resets back to the normal state (e.g., from CLOSE to OPEN for an NO switch).
   • Record the reset pressure.
6. Repeat for Repeatability:
   • Repeat the test at least once to determine repeatability.