Pressure switches are widely used within many applications in industrial facilities. The basic function of a pressure switch is to detect a pressure change and convert it into an electrical function typically on/off or off/on.
These products have been around for decades but sometimes customers still need help when looking to select a pressure switch to solve a problem or improve the performance of a process in their facility.
basic considerations
In this article, UEI will review some basic considerations involved in making to make the right decision when it comes to selecting an industrial pressure switch.
Most industrial instrumentation supplier websites include a product selector for customer use. Let’s look at some considerations for each step.
Hazardous or General Locations
It is important to know what type of environment, the pressure switch would be installed
It is important to know what type of environment the pressure switch would be installed in general or hazardous locations; indoors or outdoors; exposed to salt air; inside a control panel; or in high ambient temperature.
Hazardous locations are where explosion or fire hazards exist due to the presence of flammable gases, flammable or combustible liquid-produced vapors, combustible dust, or ignitable fibers or flyings. Products used in those areas need to be designed to prevent or mitigate such dangers.
Micro-switch considerations
Micro-switches are available in a variety of configurations. The most common is 15A, 480VAC SPDT (single pole, double throw). The advantage of an SPDT micro-switch is that it offers to wire either to open or close on pressure change.
Other micro-switches often available include 1A which is useful when working with a PLC, or at the upper end, 30A when switching certain high-load motors.
- DPDT
A DPDT (double pole, double throw) micro-switch would provide two functions off one micro-switch.
If a low-high limit alarm and shutdown were required, there are pressure switches that include two SPDT micro-switches that are independently settable.
Setpoint
The micro-switch could be wired to open or close when the set point is achieved thereby triggering an event
The application set point is the value reached by rising or falling pressure at which the micro-switch changes states.
Depending upon the pressure switch function, the micro-switch could be wired to open or close when the set point is achieved thereby triggering an event such as an alarm, equipment shutdown, or powering up secondary equipment. Ideally, the set point should fall into the middle of the pressure switch range for best repeatability.
Deadband
Deadband is the on-off differential required to reset the micro-switch. This value may be fixed or adjustable.
Deadband may be an important factor to consider depending on the application requirements.
System pressure
Other factors to consider are vacuum and/or surge pressure that could affect switch operation
Knowing normal and maximum system pressures will help in selecting a pressure switch with appropriate minimum and maximum operating parameters. This would involve maximum working pressure, over-range pressure, and proof pressure specifications.
Other factors to consider are vacuum and/or surge pressure that could affect switch operation. The relationship between the set point and system pressure has a direct effect on switch performance and life.
Process media and wetted parts
The pressure connection and sensor are known as wetted parts since they come into direct contact with the process media. Sensor materials are typically either elastomer (e.g., Buna-N, Teflonâ) or metallic (e.g., Brass, Stainless Steel) with metallic pressure connections.
The process media must be compatible with the wetted parts material. Process media temperature should also be considered as each of the different wetted materials would have differing operating properties. With careful consideration of all the factors listed above, choosing a pressure switch is a snap.