By the end of this article, you will know how to test a pressure switch easily and effectively.
All pressure switches should have a Deadband threshold to operate optimally. Deadband is the difference between the rising and falling pressure setpoints that can be easily obtained. Deadband establishes a threshold for the electrical connections in a device to close and open. As a handyman, I often need to check and troubleshoot Deadband issues of devices like HVAC refrigerators. Knowing your pressure switch Deadband threshold is key to understanding and troubleshooting your pressure switch and all other devices that are being controlled by it.
In general, the process of checking if your pressure switch has a Deadband threshold is straightforward.
- Disconnect the pressure switch from a device it regulates
- Calibrate the pressure switch with a DMM calibrator or any other ideal calibrator
- Connect the pressure switch to a pressure source, such as a hand pump attached to a gauge
- Raise the pressure until the pressure switch changes its state to closed from the open state
- Record the rising setpoint pressure value
- Reduce the pressure gradually until the pressure switch changes state to open from the closed state
- Record the falling pressure setpoint
- Compute the difference between the rising and falling pressure best pints
I will go deep into this.
Testing a Pressure Switch
Testing a pressure switch is not a complex process. The procedure below will help you accurately test your pressure switch’s Deadband threshold accurately.
Set Up the Device
First, you need to set up the device; the steps below will help:
Step 1: Disconnect the Pressure Switch
Disconnect the pressure switch from a device it controls, nice and slow. The devices operated by pressure switches include HVAC, air pumps, gas cylinders, and many more.
Step 2: Calibration of The Pressure Switch
Accurate calibration of the device is necessary to detect and rectify mishaps in the setpoint and the Deadband of the switch. Additionally, calibration saves time by reducing the number of equipment you must use. I recommend fetching an appropriate calibrator to automate the calibration process. (1)
Now, connect a calibrator (or DMM) to the pressure switch’s Common and NO output terminals.
A DMM calibrator measures an “open circuit.” Also, ensure your DMM calibrator can handle the voltage under measurement – when measuring Voltage in Alternating Current.
Step 3: Link the Pressure Switch to a Pressure Source
You can connect the pressure switch to a hand pump attached to a gauge.
Step 4: Increase the Pressure of The Pressure Switch
Raise the source pressure to a setpoint of the pressure switch until it (the pressure switch) changes state to “close” from “open.” Note down the pressure value immediately after the DMM depicts a “short circuit”; however, when using a calibrator, it will record the value – you don’t have to note it down manually.
Step 5: Reduce the Pressure Switch Gradually
Raise the pressure up to the maximum pressure of the switch. Then, reduce the pressure gradually until the pressure switch changes state from close to open. Record the pressure value. (2)
Step 6: Compute the Deadband Threshold
Recall the following pressure values that you recorded in the previous steps:
- The setpoint pressure – Recorded at increasing pressure.
- The setpoint pressure – Recorded at falling pressure.
With these two figures, you can compute the Deadband pressure from the formula:
Deadband Pressure = Difference between the rising setpoint pressure value and the dropping pressure reset point.
The Implications of a Deadband Value
The main goal of having a Deadband (different between increasing and decreasing pressure set points) is to avoid the chattering of the switch. Deadband introduces a threshold for when the electrical system should open or close.
So, a pressure switch must have a Deadband to function well. If you don’t get a Deadband, your pressure switch is faulty and requires replacement or repair – depending on the damage.
As reiterated, Deadband threshold pressure should be significant for your pressure switch and the device it operates to function optimally. The process is easy: set up the pressure switch, connect it to a device, increase pressure, decrease pressure, record the setpoint pressure values, and compute the Deadband threshold.
I believe this guide’s detailed steps and concepts help you to test your pressure switch in the easiest way possible and to understand its importance.
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(1) calibration process – https://www.sciencedirect.com/topics/engineering/
(2) maximum pressure – https://www.sciencedirect.com/topics/engineering/