In the pressure calibration industry, the terms sensors, transducers and transmitters are often used interchangeably. However, their differences are important for manufacturers and their clients to ensure the proper instrument is being employed for specific jobs.
Sensors in Calibration
Sensors are fundamental in the pressure calibration industry. According to the International Vocabulary of Metrology (VIM), a sensor is an element of a measuring system that is directly affected by a phenomenon, body or substance carrying a quantity to be measured.
“At Mensor, we use a wheatstone bridge sensor that changes resistance based on the amount of pressure applied to its surface. This change in resistance is measured and translated, through Ohms law, to a voltage in the transducer,” said Derek Zarate, Mensor Product Engineer.
While the wheatstone bridge (the "sensor") signal could be displayed on a simple ohmmeter, in order to amplify and adjust this signal into a quantifiable analog or digital output, a sensor requires a "transducer." Mensor transducers acquire the signal from the sensor; this voltage is sent to an analog-to-digital converter and then into a microprocessor where the signal is characterized and converted to a readable and accurate digital output.
Transducers in Calibration
According to the VIM, a transducer is a device used in measurement that provides an output quantity having a specified relation to the input quantity. The signal coming from a pressure transducer is proportional to the pressure being applied to the sensor.
For most pressure transducers, the input quantity is the applied pressure and the output is the reading. A transducer takes the analog signal from the sensor and translates that raw data into a reading. Mensor transducers can have multiple outputs including digital, voltage or current. Pressure transducer readings are often displayed in different units of measure such as bar, psi or Pa.
Transmitters in Calibration
While transducer and transmitter are often used synonymously, the term transmitter commonly refers to a specific type of transducer that sends the pressure reading as a current. Transmitter output readings range roughly from 4 to 20 mA in relation to the pressure input. Working similarly to a transducer, the transmitter takes raw data from the sensor and converts it into electric current. Since electric current is one of the easiest ways to send data over great distances, their readings are often transmitted to a remote device. This can aid in safety and convenience for users to monitor pressure, temperature and other process data.
It’s common to hear to hear these terms used in place of each other; even industry experts refer to all of these devices as sensors. Some lump them all together as transducers or transmitters. However, in calibration, accuracy is king. The terms used to differentiate these devices are what ensures users get the most accurate and applicable technology for their application.