The terms pressure sensors, transducers, transmitters and switches are very commonly used in the industry.
But what is their actual difference?
Sensors vs Transducers vs Transmitters vs Switches
Strictly speaking, their simplified technical definitions are as follows:
Sensor or transducer: A device that translates a physical property (pressure, temperature, humidity etc.) to an electrical signal.
Transmitter: A sensor that conveys data over long distances.
Switch: A sensor that holds a threshold (X) and outputs true or false indications. For example, if measured pressure > (X) output true otherwise output false.
The above definitions can be applied to any type of sensor and not only pressure ones.
Many organizations provide their own definitions for sensors and transducers including the Institute of Electrical and Electronic Engineers (IEEE), the American National Standards Institute (ANSI), the Instrument Society of America (ISA) and others.
Moving a step further than the strict definitions, these terms hold some respective characteristics that could be utilized when required to search for the appropriate part for your system solution.
These devices usually have small mechanical body, have direct contact with the measured medium, require small supply voltage (3.3V, 5V) and have digital (SPI, I2C) or analog (millivolt, 0.5-2.5V, 0.5-4.5V, 0-3.3V, ratiometric) output.
An example is shown below:
Further reading: Learn about pressure sensors used in Healthcare
Pressure transducers or Capsules
These devices usually are bulkier than pressure sensors, have indirect contact with the measured medium, require small supply voltage (3.3V, 5V) and have digital (SPI, I2C) or analog (millivolt, 0.5-2.5V, 0.5-4.5V, 0-3.3V, ratiometric) output.
An example is shown below:
These devices usually have a bigger mechanical envelope than the rest of the categories, have indirect contact with the measured medium, can be supplied by high voltages (up to 32V) and have communication protocols used for long distances. The most common communication protocol for pressure transmitters is 4-20mA.
Examples are shown below:
Pressure switches can be found in any of the above types, with the most common being in a transmitter.
Picking the right pressure sensor
In order to pick the right sensor for your design, there are four main questions that you need to ask:
What type of pressure sensor do you require? Absolute, gauge, differential?
How harsh is the environment you are going to place the sensor into? Do you expect overpressure conditions? In general, medium isolated pressure sensors can withstand more harsh environments. Learn more about industrial pressure sensors.
How much real-estate do you have available at your design? If you have tight space in your PCB or in your mechanical envelope in general, then a board mountable sensor might be the way to go.
What is the communication protocol? In general, the communication protocol selected is the one available from the controlling system (microcontroller, PLC, etc). For new designs, we recommend the use of digital communication protocols (if possible) as the bidirectional communication enables features such as self-test, status check etc. that make the system level integration more robust.
Continue reading: Capacitive vs Piezoresistive Pressure Sensors – Which one to pick?
A very important rule of thumb is always to pick the pressure sensor that has the best accuracy (lowest total error band) possible for the available budget. When picking a pressure sensor, the anticipated lifetime of the total system should also be considered.