Industrial Pressure Measurement Guide: Selecting Transducers, Transmitters, and Electronic Switches
Pressure monitoring plays a key role in industrial, civil, and environmental settings. It supports many important applications. In this article, we aim to help our customers understand pressure transducers and choose the right sensing instrument for their needs.
Short on Time? Send any questions through our contact page here, or call us directly on 1300 236 467
Understanding Pressure Reference Points: Gauge, Absolute, Differential & Sealed
There are four main pressure reference types: gauge pressure, absolute pressure, differential pressure, and sealed gauge pressure. Knowing which type you need to monitor will help you choose the right pressure instrument.
Gauge Pressure vs Absolute Pressure: Key Process Differences
Gauge pressure is measured against the surrounding atmospheric pressure (101.3kPa at sea level). The sensor vent lets local barometric changes balance the diaphragm's back pressure. This type is often used in open tanks, hydraulic lines, and compressed air systems.
Absolute pressure is measured against a sealed, perfect vacuum (0 bar absolute). It is essential for barometric monitoring, vacuum distillation, altitude measurement, and closed-loop process reactors where weather changes must not affect readings.
Differential Pressure (DP) & Sealed Gauge
Differential pressure measures the difference between two separate pressure ports (P/high and P/low). It is key for flow calculations using orifice plates or venturi tubes, monitoring filter clogs (clean versus dirty side), and sensing levels in pressurised vessels.
A sealed gauge references a sealed chamber set at standard atmospheric pressure, not vented to the outside. This is useful in harsh washdown or submerged environments where moisture entering through a vent tube could damage the electronics.
Pressure Transducer vs Transmitter vs Switch: Core Differences & Architecture
The right pressure instrument can use any of these pressure reference points. The four main types are pressure transducers, pressure transmitters, pressure switches, and pressure gauges. Each type offers different options depending on how and where it will be installed.
Pressure Sensor (Sensing Element)
The pressure sensor element is effectively the diaphragm that deforms under pressure. The diaphragm can be a Wheatstone bridge, a piezoresistive silicone die, a piezoresistive ceramic diaphragm, a piezoelectric element, a capacitive cell, or a thin-film strain gauge. The pressure sensor is the foundation of all pressure instruments. or less effective across different pressure application mediums. Below, we’ve included a quick table showing which applications these sensing elements can support.
Diaphragm Sensing Technologies & Media Compatibility
Sensor Element | Suited Application |
|---|---|
| Piezoresistive (Silicone) | Clean gases, general industrial hydraulics, pneumatic lines |
| Piezoresistive (Ceramic) | Wastewater, aggressive acid/chemicals, food & beverage |
| Thin-Film / Strain Gauge | Heavy mobile hydraulics, surge vessels, water hammer applications, engine testing. |
| Capacitive Cell | Cleanroom differential pressure, HVAC draft monitoring, critical process DP transmitters |
| Piezoelectric | Explosive blast testing, ballistic pressure, ultra-high-speed cavitation, water hammer diagnostics (not ideal for static pressure). |
Pressure Transducers: Signal Characteristics & Millivolt Outputs
Pressure transducers convert diaphragm movement into a corresponding voltage signal (in mV or V).
Most pressure transducers use a piezoresistive strain gauge and a Wheatstone bridge. They apply an excitation voltage to measure resistance changes. A signal conditioner or transmitter then boosts the millivolt signal, linearises it, and converts it to a standard format like 4-20mA or sometimes a higher voltage (0-10V), allowing longer cables to a control unit.
Pressure Transmitters: 4–20 mA Current Loops & Industrial Fieldbus
A transmitter is a transducer with added circuitry that outputs a standard industrial signal, such as 4-20mA, or a digital protocol like HART or Modbus RS-485. Because current signals are unaffected by line resistance or voltage drop, pressure transmitters are widely used in process automation, water systems, and manufacturing.
Pressure Gauges: Local Indication vs Continuous Telemetry
Pressure gauges are self-contained and provide local readouts for direct operator monitoring at the point of measurement, without necessarily transmitting data to a PLC or SCADA network.
Pressure Switches: Mechanical Deadband vs Programmable Electronic Trip Points
Pressure switches work differently than transducers, transmitters, and gauges. While those focus on continuous monitoring, a pressure switch provides direct threshold control.
Pressure switches come in two types: mechanical and electronic. Both types open or close a circuit to start pumps or set off alarms when a set pressure is reached.
Mechanical Pressure Switch
Mechanical pressure switches use a diaphragm, piston, or bellows to press a calibrated spring and trigger a microswitch. They are tough, use only mechanical parts, need no power supply, and let you adjust the setpoint with a hex screw.
Mechanical pressure switches have many uses today; however, the technology isn’t as advanced as its electronic counterpart, which limits deadband settings and increases wear and tear over time.
Electronic Pressure Switch
Using the same type of pressure sensor as transducers, transmitters, and gauges, the electronic pressure switch uses a piezoresistive or ceramic cell combined with a microcontroller. Because they are electronic, trip and reset points are programmable, with no mechanical switch contacts.
In more modern variations, electronic pressure switches can feature switching outputs and a 4-20mA I/O link analog output, taking on more characteristics of pressure transmitters.
Specialised Pressure Instruments for Civil & Mechanical Applications
Pressure instruments come in a handful of variations, each designed for specific pressure-monitoring applications. These include hydrostatic level transmitters, differential pressure cells and smart/digital pressure transmitters.
Hydrostatic Level Transmitters: Submersible Probes & Flush Diaphragms
Hydrostatic level transmitters are submersible probes that measure level or pressure in a liquid-filled vessel, tank, or pipeline.
There are two main types: the classic hydrostatic transducer probe, which is a cylinder with holes at the end, and the flush-mounted pressure transmitter, which faces the liquid directly through a recessed port. The flush-mounted type helps prevent mud, debris, or other materials from building up or clogging the instrument.
Differential Pressure Cells: Flow, Filter Clogs & Sealed Vessels
Differential pressure cells measure the pressure difference between two process taps using a single sensing diaphragm. Instead of comparing to the atmosphere or a vacuum, they only measure the difference between two points.
Differential pressure cells can be used for various applications, including;
- Filter monitoring: detecting blockages by measuring pressure drop across a filter element
- Flow rate: measuring pressure drop across an orifice plate or venturi tube.
- Pressurised Tank Level: Determines the liquid head in a sealed vessel by subtracting headspace/vapor pressure from total bottom pressure.
Smart Pressure Transmitters: HART, IO-Link & Active Thermal Compensation
Combining a pressure sensor with an onboard microprocessor to calculate, compensate and communicate bidirectional data, rather than outputting a simple one-way analog current or voltage.
These pressure transmitters provide accurate, continuous readings, real-time device health checks, process temperature data, and remote configuration. They often support advanced communication protocols like HART, IO-Link, Modbus RS-485, or Profibus.
With advanced communication and onboard processing, these transmitters let users make remote adjustments and actively correct for temperature changes, reducing measurement drift.
Dynamic Data Acquisition & Digital Bus Protocols (USB & RS-485 Modbus)
Most industrial applications typically use analogue 4-20mA loops; however, as industrial process technologies advance, many pressure transmitters now support digital protocols for high-speed dynamic logging and multi-drop field networks.
USB Pressure Acquisition
Across the ESI range of pressure transmitters, USB connectivity is becoming standard. These plug-and-play USB pressure transducers, like the GS4200-USB and dynamic GD4200-USB, reduce the need for costly external I/O data acquisition cards by converting signals directly at the sensor.
This move to USB transducers draws bus power directly from the computer port. It supports sampling rates up to 1,000 readings per second (1,200 Hz), ideal for complex applications requiring transient capture, burst testing, and automated 5-step leak verification. The ESI-USB pressure transmitter range supports up to 16 digital sensors live-streaming simultaneously from a single USB hub.
RS485 Serial Communications
For digital transmission over long field distances, RS485/Modbus RTU pressure transmitters like the ESIGS4400 series or LEEG SMP131 transmit noise-free digital data over distances from 500m to 1000 m. This process can daisy-chain up to 32 transmitters across a single BUS, enabling centralised multi-port data logging while keeping sensitive monitoring PCs safe from the harsh process environment.
Learn more about RS485 Pressure Transmitters in our blog here.
Need Support? Contact Us Today!
If you need some help with finding the right Pressure Transducer for your upcoming project, please give us a call! Send any questions through our contact page here, or call us directly on 1300 236 467
Image
