What’s the difference between sensor, transducer and transmitter？

The words ‘sensor’, ‘transducer’ and ‘transmitter’ are often used interchangeably. There is a difference, but the chosen term of different devices varies depending on context and manufacturer. First let’s have a look at the definitions of ‘sensor’ and ‘transducer’:

Sensor:?A sensors measure a physical quantity (temperature, light, magnetic field etc.) and convert it to a readable output.

Readable don’t always mean useful, a common output is change in resistance.

Transducer:?A transducer converts one energy form to another. In this context is a transducer the signal conditioning. So, the transducer transforms the readable output to a useful output signal, for example 0-10V.

Most devices contain a sensor and signal conditioning, so is this device a sensor or a transducer? By definition it’s both, the term used depends on the context and manufacturer. In the context of position measurement, the device is commonly called sensor, but the term transducer also occurs. In the context measuring pressure, level, flow etc. is transducer the word of choice. In this context ‘Transmitter’ is another term.

Transmitter:?One definition is that pressure transducers do not apply any signal conditioning and a pressure transmitter apply conditioning. So, a pressure transducer is a pressure sensor with mechanical housing and electric connector. Trafag uses this definition so all devices that apply signal conditioning is called ‘pressure transmitter’.

Another, commonly used, definition is that a transducer only amplifies the signal from the sensor and a transmitter converts the signal. An mV output from the sensor is amplified to 0-5V, 0-10V etc. output in a transducer, and a transmitter converts the output signal to for example 4-20 mA or a digital output such as CANopen.