# sensor vs transducer



## EBFD6 (Aug 17, 2008)

What is the difference between a sensor and a transducer.

I was looking at a website that sells control parts and they had pressure sensors, pressure transducers, current sensors, current transducers, and I realized that I really had no idea what the difference was.

I have wired circuits using current sensing relays and such, where current flows through a circuit and that wire is routed through the donut on the CSR which in turn closes the contacts thus allowing something else to happen, but I don't recall ever wiring a transducer.

After doing a little bit of google research, I think I may have a grasp on things but would like to get some confirmation.

Basically, a sensor measures and will activate at a predetermined value (for instance a pressure sensor that is set for 100 psi will be activated, contacts open or close, when the pressure it is measuring reaches 100 psi). On the other hand a transducer takes a measurement and converts it to an electrical value (ie.. 100 psi is measured by the transducer and then converted to a 4-20mA signal, or 0-5v, etc.) for inputting into a plc or something.

Am I correct?

If not, any opinions? Clarification?


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## John (Jan 22, 2007)

EBFD6 said:


> What is the difference between a sensor and a transducer.
> 
> I was looking at a website that sells control parts and they had pressure sensors, pressure transducers, current sensors, current transducers, and I realized that I really had no idea what the difference was.
> 
> ...


Close :thumbsup:

Try this:

A sensor is a device that measures something physical and converts it into some type of an electrical signal. A water meter would be an example of converting mechanical turning of the turbine by water flow and converting it to switched pluses. The input would be mechanical and the output would be digital.

A transducer is a device that converts one type of energy to another. A good example would be to convert pressure (psi) to current (0-20 ma, 4-20ma, 0-10 volt) The input would be analog and the output can be either analog or digital.


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## 5volts (Jan 11, 2008)

EBFD6 said:


> What is the difference between a sensor and a transducer.
> 
> I was looking at a website that sells control parts and they had pressure sensors, pressure transducers, current sensors, current transducers, and I realized that I really had no idea what the difference was.
> 
> ...


 
First you have your analog input device:

Pressure transmitter

Flow meter

temperature probe

(RTD) Resistance temperature Detector 


So for instance on a pasteurizer if you are using a RTD to detect the temperature of the water on a hot tank as the resistance changes the transmitter will send a 4 to 20 ma signal to the PLCs Analog input card.

If you are using AB PLCs in your PLC you would set up A (BTR) Block tranfer read and a Block transfer write (BTW) instruction. For your Analog Input and output modules. This is your configuration so you will be able to read and write those 4 to 20 ma signals 

Also in your PLC your PID (proportional integral derivative) instruction is what is going to control your transducer or also known as a I/P through your PLCs Analog Output card. 

If your RTD senses that the tank is starting to cool it will send a signal to your analog input card and your PID will determine how much more hot water will need to be brought in to the tank to bring the tank up to temp.

This is just one example,


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## fisherj (Jan 26, 2009)

A sensor is a very generic term and refers to any device that can detect or measure a physical property.

A transducer is a bit more specific and refers to a device that converts a non-electrical signal into a electrical signal.


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## EBFD6 (Aug 17, 2008)

Thanks for the replies!

Between the replies here, and a little more web surfing, I think I have a grasp on the concept.

I have done a decent amount of control work through the course of my career, but I am always looking to learn more.

I am glad to see a category dedicated to controls/PLC's on this forum, and hope to see some interesting discussions, and hopefully learn some things.:thumbsup:


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