Pressure Switches - Mechanical or Electronic?
Pressure switches are available in two different design types, mechanical or electronic.
How Mechanical Pressure Switches Work
Directly behind the pressure switch’s process connection port is a diaphragm, piston, or bellows chamber. The medium’s pressure deforms or moves against an end stop and the chamber acts directly onto a micro switch. The setpoint can be adjusted by an adjustment screw that repositions the microswitch within the movement range, so that it is triggered at the required pressure.
How electronic pressure switches work
Much like a pressure transmitter, the sensor inside the pressure switch’s port can be described as a plate that separates the media from the electronics.
On the opposite side of the plate is a transducer that converts any deflection in the plate into a measurable signal. (The definition of transducer is a device that converts one form of energy into another).
The transducer’s components can take the form of either a resistive bridge or strain gauge type sensor, piezo effect, thin sputter film, or silicon on sapphire to name a few.
The variations are dependent on the intended application of the pressure switch, considering chemical or corrosion resistance, temperature, accuracy, cost, and pressure range.
Instead of transmitting the analog signal as a 4-20mA or 0-10V, an electronic pressure switch uses an electronic logic comparator to compare the analogue against a trim pot (variable resistor) value and convert that result into an ON or OFF output signal, which triggers an electronic relay/switch.
Choosing a Pressure Switch for Your Application
Both types of pressure switch have their pros and cons.
Advantages of mechanical pressure switches:
- Lower cost
- Higher current ratings – can switch pumps, motors, or valves directly
- Being a passive device, no power source is required
Disadvantages of mechanical pressure switches:
- Not effective or reliable for switching low power control signals (e.g. PLC inputs), unless an expensive switch with gold contacts is used.
- To set the switch point pressure, some mechanical pressure switches have the adjustment screw hidden underneath the DIN plug connector, and the set-up process is not easily carried out on site.
- More moving parts translates to lower reliability or longevity
Advantages of electronic pressure switches:
- Suitable for process control applications
- Setpoint adjustment easily accessed
- High accuracy and repeatability
Disadvantages of electronic pressure switches:
- Requires a power source, typically 10-30VDC
- Higher cost than mechanical pressure switch
Typical Applications for Mechanical Pressure Switches
- Hydraulics over or under pressure limits
- Mobile moving machinery
Typical Applications for Electronic Pressure Switches
- Process control
- Packaging machines & automation
ADM offers both mechanical and electronic pressure switches.
If you would like any further information on pressure switches, please do not hesitate to contact ADM Instrument Engineering on 1300 236 467.