Industrial pressure sensor types
Industrial pressure sensors convert the force exerted by a liquid or gaseous fluid into a proportional electrical signal, enabling precise monitoring and control of processes. These instruments are used in control loops ranging from partial vacuum (-1 bar / -14.5 psi) to high pressures of 690 bar / 10000 psi, and their selection depends on factors such as fluid type, required accuracy, and environmental conditions. The fundamental types include pressure switches, transmitters, and differential sensors, each with specific construction principles and output characteristics.
Modern pressure sensors typically operate on the strain gauge principle. An elastic element, usually a stainless steel diaphragm, deforms under process pressure. This mechanical deformation changes the electrical resistance of a coupled piezoresistive cell, generating a Wheatstone bridge signal proportional to the pressure. Solid-state sensors use the same principle but integrate temperature compensation on the chip, achieving service lives exceeding 50 million cycles. In digital instruments, the analog signal is converted via an ADC before transmission.
Main Types
Section titled “Main Types”| Type | Measurement Principle | Typical Pressure Range | Output Signal | Common Application |
|---|---|---|---|---|
| Mechanical pressure switch | Deformation of bellows or piston against a calibrated spring | -1 to 690 bar / -14.5 to 10000 psi | NO/NC contact (electrical switching) | Pump control, overpressure alarm in hydraulics |
| Electronic pressure switch | Strain gauge with switching electronics | -1 to 600 bar / -14.5 to 8700 psi | Discrete PNP/NPN output, optional analog output | Injection molding machines, test benches |
| Analog pressure transmitter | Piezoresistive sensor with amplifier and compensation | 0 to 690 bar / 0 to 10000 psi | 4-20 mA, 0-10 V, 1-5 V | PID loop control in continuous processes |
| Differential pressure transmitter | Pressure measurement in two chambers separated by diaphragm | 0 to 10 bar / 0 to 150 psi (differential) | 4-20 mA, HART, IO-Link | Filter monitoring, clean rooms, flow measurement by orifice plate |
| Digital sensor / smart transmitter | Primary cell with microcontroller and display | -1 to 690 bar / -14.5 to 10000 psi | IO-Link, Modbus, 4-20 mA with HART | Food industry (tri-clamp connection), PLC-connected systems |
Technical Characteristics
Section titled “Technical Characteristics”| Parameter | Typical Value |
|---|---|
| Accuracy (at 25 °C / 77 °F) | 0.25 % FS (high-end transmitters); 0.5 % FS (standard models) |
| Response time | 1 ms to 5 ms |
| Ambient temperature range | -40 to 125 °C / -40 to 257 °F |
| Body material | Stainless steel 316L (general industry); engineering plastic for compressed air |
| Process connection | 1/4“ NPT / 6.4 mm, G 1/2“ / 12.7 mm, sanitary tri-clamp 1-1/2“ / 38.1 mm |
| Protection degree | IP67 to IP69K (depending on model) |
| Standardized output signals | 4-20 mA (current loop), 0-10 V, IO-Link |
Common Applications
Section titled “Common Applications”Industrial pressure sensors are installed in hydraulic and pneumatic systems to ensure stable pressure between 0 and 690 bar / 0 to 10000 psi and prevent failures. In filter and silencer monitoring, differential pressure transmitters detect pressure drops below 100 mbar / 1.45 psi, signaling maintenance needs. Smart transmitters with sanitary tri-clamp connections are used in the food and pharmaceutical industries to measure process pressure with 0.3 % FS accuracy in typical ranges of 0 to 25 bar / 0 to 363 psi. In buildings and clean rooms, low differential pressure sensors maintain positive pressurization with a span of 0 to 400 inches of water column (inH₂O), equivalent to 0 to 0.99 bar. Mechanical pressure switches protect heating and cooling circuits with adjustable set points between 0.5 and 100 bar / 7.25 to 1450 psi.
Advantages and Disadvantages
Section titled “Advantages and Disadvantages”| Aspect | Advantages | Disadvantages |
|---|---|---|
| Mechanical switches | Simplicity, robustness, no power required, long life in harsh environments. | Fixed or poorly adjustable trip point, appreciable hysteresis, no proportional output. |
| Electronic switches | High repeatability (0.1 %), solid-state (over 50 million cycles), low hysteresis. | Require power supply, more sensitive to electromagnetic interference. |
| Analog transmitters | Proportional output ideal for analog control, high accuracy, wide range of ranges. | Requires additional element for switching (external relay). |
| Digital transmitters | Bidirectional communication, self-diagnostic, remote calibration, multiple simultaneous parameters. | Higher cost, requires industrial network integration, more complex configuration. |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the difference between a pressure switch and a transmitter?
Section titled “What is the difference between a pressure switch and a transmitter?”A pressure switch provides a binary signal (switching) when pressure exceeds a predefined set point, while a transmitter delivers a continuous analog signal proportional to the measured pressure value over a range of 4-20 mA or 0-10 V.
Which type of electrical output is most common in industrial pressure transmitters?
Section titled “Which type of electrical output is most common in industrial pressure transmitters?”The 4-20 mA current loop output with two-wire power supply is the most widespread, as it allows cable runs of up to 1000 m / 3281 ft without significant signal degradation and with good noise rejection.
How does ambient temperature affect the accuracy of a pressure sensor?
Section titled “How does ambient temperature affect the accuracy of a pressure sensor?”Compensated sensors maintain a specified accuracy of ±0.25 % of span at 25 °C / 77 °F, but thermal drift adds an additional maximum error of ±0.04 % FS/°C. For example, at 85 °C / 185 °F the total error can double the standard nominal accuracy.
What maintenance do pressure sensors require?
Section titled “What maintenance do pressure sensors require?”Most sensors with a 316L stainless steel body and flush diaphragm are maintenance-free in clean fluids. It is recommended to inspect the diaphragm annually if the fluid contains solids, and models with a siphon or needle valve should be purged every 6 months to prevent condensate buildup.
Can pressure sensors be used for liquids and gases interchangeably?
Section titled “Can pressure sensors be used for liquids and gases interchangeably?”Many industrial transmitters are designed for both media as long as the sensor materials are compatible. However, applications with gases at high pulsation frequencies require specific snubbers, while viscous liquids may need flush diaphragms and T-mountings to prevent clogging.
What factors determine the choice of a pressure sensor for a specific application?
Section titled “What factors determine the choice of a pressure sensor for a specific application?”The choice depends mainly on the pressure range, chemical compatibility of the fluid with the diaphragm (316L steel, Hastelloy, ceramic), required accuracy (typically between 0.1 % and 0.5 % FS), type of process connection, and control signal needed (discrete, analog, or digital). Also influential are the working temperature, which can range between -40 and 125 °C / -40 and 257 °F.
References
Section titled “References”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/flow-meters-d_493.html
- plcacademy.com: https://www.plcacademy.com/thermocouple/
- automationdirect.com: https://www.automationdirect.com/adc/overview/catalog/process_control_-a-_measurement/pressure_sensors