Sensors in process industry

Why sensors are used in process industry?

Automation devices used for the realization of control techniques from a process such as hardware, PLC software or microcontroller can only run well if the required process data can be obtained validly, for example information such as temperature, distance, or angular speed.

One type of feedback that is often needed by an industrial control system is the position of one or more operating components to be controlled. Sensors are devices that are used to provide information about the presence or absence of objects. The sensor provides information on the process of control and regulation of the process.

Process information from the production process, process technique or other automation fields are usually not present as electrical quantities, but as the distance of a path, angle, pressure or level, also as a physical quantity. So that the process can run automatically, the physical quantity must be measured. The sensor detects the physical quantity of non-electric quantities and converts them to electrical quantities such as voltage. A commonly used measure is electric current (for example 4 mA … 20 mA).


Type of sensor to measure different physical process variables, there are two types of sensors used as follows:

  • Passive sensor
  • The sensor is active

Passive sensors have impedances in the form of resistance, inductance, capacitance, or a combination of which changes in magnitude to be detected. Passive sensors require a power supply to generate electrical signals.

Active sensors form non-electric physical quantities that are measured directly into electrical signals. Active sensors are energy converters that do not require additional energy. In principle, the sensor consists of two components, namely sensor elements and signal processing components, which will convert the signal from the sensor element into an electrical output signal.

In the mechatronics system, for example, if an object has fallen below a certain distance, whether it is a direct distance measurement, or whether the liquid is above a certain level in a container. On the other hand, also to check whether the thread is cut, or if the cutting tool is not peeled or broken on a CNC machine.

To capture all the information, various sensors are used. Sensors can be broadly classified into:

  • Binary sensor (output signal in the form of ON / OFF signal, voltage 0 V / 24 V, current 0 mA / 20 mA)
  • Digital sensor (detecting numerical distances, for example increment displacement sensors)
  • Analog sensors (detection of time-dependent variables such as temperature, pressure, thickness measurements.

Contact arrangement:

Contacts are available in several configurations. Contacts can be normally open (NO), normally closed (NC), or a combination of NO and NC contacts, and change over (CO) contacts. The circuit symbol is used to indicate an open or closed path from an electric current. Contacts below as NO or NC. The standard method of contact designation is an indication of the circuit condition produced if the contact actuation device is inactive or in an inoperative state.


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