The basic steps for testing a normally closed valve with a multimeter are as follows
1. Set the ProcessMeter process multimeter to output mode and use the corresponding current range suitable for the locator.
2. Insert the output current test line into the mA output jack.
3. Move the rotary function switch from the OFF position to the first mA output position above, and select the 4-20 mA range.
4. Connect the process multimeter to the input terminal of the valve positioner.
To determine if the locator fully closes the valve at 4 mA, use the button to adjust the output current to 4.0 mA. The valve should be closed.
6. Simultaneously observe whether the valve is moving, press the Coarse down arrow button once to reduce the current to 3.9 mA. The valve should have no movement.
7. When setting the starting position of the valve to open, ensure that there is no reverse pressure on the actuator (this pressure keeps the valve closed when the controller input is 4.0 mA). For spring closed valves, there is no pressure on the diaphragm. For double acting piston actuators, there should be no pressure on one side of the piston. To ensure that there is no reverse pressure when closing the setting, the starting point of the valve opening can be set between 4.1 and 4.2 mA.
8. Check that the valve is open, press the Coarse up arrow button, and start adjusting from 4.0 mA. Each time the Coarse arrow button is pressed, the current increases by 0.1 mA. The zero adjustment function of the valve positioner should be adjusted to set the valve to the corresponding closed mode.
To check the fully open position of the valve, known as span position check, use the Range button to adjust the output current to 20 mA and wait for the valve to stabilize. While observing and feeling the valve movement, press the Coarse up arrow button once to set it to 20.1 mA. The valve movement should be minimized and can be adjusted using the span adjustment on the locator.
10. Use the Coarse control button to adjust the current up and down between 20.1 mA and 19.9 mA. The valve stem should not move between 20.1 and 20 mA, and should move slightly between 20 mA and 19.9 mA.
In most valves, the zero point and span set point of the valve controller interact with each other; Therefore, it is best to repeat the test for fully closed and fully open positions, adjust the valve position correctly until no further adjustment is needed.
