What is a Sensor? Different Types of Sensors, Applications

Learn about what a sensor is, what it can do, and how it can be used in process control

Different types of sensors are a part of everyday life at home and work. There’s probably not a day that goes by where you aren’t impacted in some way by a sensor.

In this article, we’re going to talk about what a sensor is, what it can do, and how it can be used in process control. You’ll also learn the various applications of sensors in industrial environments.

Applications of different types of sensors

OK…off we go. What is a sensor? A sensor is a device that senses something. Today we have sensors that can see, feel, hear, smell, and even taste.

Without sensors, our home and work lives would be quite difficult. For example, as you drive to work, the traffic lights at an intersection are controlled by sensors embedded in the road. These sensors detect your arrival at the intersection.

As you approach the grocery store, the door automatically opens because of a sensor.

In your plant, the batch process temperature and pressure are displayed and controlled as a result of output from Sensors.

Temperature and Pressure Sensors

Industrial sensors

In the world of instrumentation and process control, we define a Sensor as a device that detects changes in physical, electrical, or chemical properties and produces an electrical output in response to that change. 

Sensor Definition

Types of sensors

What are the typical physical properties that sensors are detecting? Let’s name a few… Level, Temperature, Flow, Pressure, Speed, and Position.

Physical Properties Sensors

Classification of sensors

From a process control perspective, we can classify sensors as either Passive or Active. 

Passive sensors

A Passive Sensor requires an external source of power to operate while an Active Sensor does not.

Passive or Active Sensors-

Active sensors

A Thermocouple is an Active Sensor as it does not require any external power supply to operate.

Active sensors examples

As a thermocouple is exposed to an increase in temperature, it will develop an increasing voltage across it.

Active Sensor

Another example of an Active sensor is a piezoelectric sensor.

Piezoelectric Sensor

Passive sensors examples

A Resistance Temperature Detector (RTD) is a Passive Sensor. It is a device that’s resistance will change with a change in temperature. To take advantage of this change in resistance, an external supply, or an excitation circuit is required to produce a change in voltage.

Resistance Temperature Detector or RTD

Another example of a Passive sensor is a Strain Gauge.

Strain Gauge

Sensors in the industry

Alright…, now that we’ve talked about different sensor types and the physical properties that they can sense, let’s discuss how they are used in the industry.

Almost every sensor used in process control will be connected to a Transmitter because a sensor’s output needs to be conditioned or amplified.

Here’s an example…We’ve already talked about a thermocouple and the voltage output created when it is heated. Unfortunately, the voltage output of a thermocouple is minuscule!

In our example, the thermocouple will produce a voltage output from 8 mV to 18 mV over a 450 degree Fahrenheit change in temperature!

In-process control, we condition that 8mV to 18mV thermocouple voltage and convert it to a 4 mA to 20 mA industry-standard signal that represents our controlled temperature range.



Ok, let’s review…

– Sensors are a part of everyday life at home and work

– A sensor is a device that can See, Feel, Hear, Smell, and even Taste.

– In-process control, sensors are classified as

  1. Passive – requiring an external excitation to produce an electrical output
  2. Active – producing a voltage output without any external excitation

– In-process control, sensors are used to measure physical variables such as Level, Temperature, Flow, Pressure, Speed, and Position.

– Sensor output voltages are very small and therefore require a Transmitter to amplify or condition the output to make it useable in process control applications.

Want to Learn More?

If you would like to get additional training on a similar subject please let us know in the comment section.

Check back with us soon for more automation control topics.

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The RealPars Team
By Ted Mortenson

By Ted Mortenson

Automation Engineer

Posted on Aug 17, 2020

Ted Mortenson

By Ted Mortenson

Automation Engineer

Posted on Aug 17, 2020

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