# what is diff between transducer & transmitter



## drsparky (Nov 13, 2008)

Transmitters are one of many types of transducers, anything that transfers one type of energy to another is a transducer.


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## wdestar (Jul 19, 2008)

A transducer is an electronic device that "Detects" and that method of detection can range from current, magnetism, capacitance, induction and so forth.

A transmitter projects the detected signal to another device.

In essence, they are opposing by definition.


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## Big John (May 23, 2010)

Like _Drsparky _said, a transducer converts directly from one source of energy to another like pressure-to-mA or temperature-to-volts. For example, a simple thermocouple is a type of transducer because it directly converts heat into a millivolt reading. There are piezoelectric sensors that are also transducers, because they directly convert pressure to a millivolt reading. 

The difference you'll notice is that those are not the common 4-20mA or 0-10V scales and if we were to package a thermocouple in an additional device that converts the signal to 4-20mA suddenly the whole thing is sold as a "thermocouple transmitter."

If it's 4 wire and not loop powered, it's a transmitter, because that indicates there's something in the equipment that is taking the raw output from the transducer and sending it through a scaling circuit and or an amplifier before transmitting it to the PLC.

There are simple 2 wire devices that will put out a calibrated range without any additional amplification, like a 4-20mA pressure transducer, but generally these types of devices work by limiting the existing loop power so they don't need amplification.

-John


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## ScooterMcGavin (Jan 24, 2011)

In the instrumentation field the term transducer a device that converts any standard signal to another standard signal. For example we have pressure transducers which convert 4-20ma to 3-15 psi for control valves or transducers which convert 0-120 volts to 4-20ma for voltage indication. Anything for a process value is considered a transmitter.


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## nolabama (Oct 3, 2007)

Great info in this thread.


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## Peewee0413 (Oct 18, 2012)

Big John said:


> Like _Drsparky _said, a transducer converts directly from one source of energy to another like pressure-to-mA or temperature-to-volts. For example, a simple thermocouple is a type of transducer because it directly converts heat into a millivolt reading. There are piezoelectric sensors that are also transducers, because they directly convert pressure to a millivolt reading.
> 
> The difference you'll notice is that those are not the common 4-20mA or 0-10V scales and if we were to package a thermocouple in an additional device that converts the signal to 4-20mA suddenly the whole thing is sold as a "thermocouple transmitter."
> 
> ...


simple way to put it


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## kobena (Nov 4, 2012)

Primary Sensing Element, or PSE: A device that directly senses the process variable and
translates that sensed quantity into an analog representation (electrical voltage, current, resistance;
mechanical force, motion, etc.). Examples: thermocouple, thermistor, bourdon tube, microphone,
potentiometer, electrochemical cell, accelerometer.

Transducer: A device that converts one standardized instrumentation signal into another
standardized instrumentation signal, and/or performs some sort of processing on that signal. Often
referred to as a converter and sometimes as a “relay.” Examples: I/P converter (converts 4-20 mA
electric signal into 3-15 PSI pneumatic signal), P/I converter (converts 3-15 PSI pneumatic signal
into 4-20 mA electric signal), square-root extractor (calculates the square root of the input signal).
Note: in general science parlance, a “transducer” is any device that converts one form of energy
into another, such as a microphone or a thermocouple. In industrial instrumentation, however, we
generally use “primary sensing element” to describe this concept and reserve the word “transducer”
to specifically refer to a conversion device for standardized instrumentation signals.

Transmitter: A device that translates the signal produced by a primary sensing element (PSE) into
a standardized instrumentation signal such as 3-15 PSI air pressure, 4-20 mA DC electric current,
Fieldbus digital signal packet, etc., which may then be conveyed to an indicating device, a controlling
device, or both.

By Tony R. Kuphaldt


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## 123 (Oct 28, 2012)

Transducer measures a value of something (like pressure...), and changes it to an analog value.
4 to 20 mA, or 0 to 10 V, or many others.
Transmitter is if for example you have a remote RTD, and want 4 to 20mA, then the transmitter
will read the RTD, and convert it to 4 to 20mA, to transmit it to the other device 
(controller or display)


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## RUI (Mar 8, 2021)

Sensors and transmitters are the concept of thermal instruments. The sensor converts non-electrical physical quantities such as temperature, pressure, liquid level, material, gas characteristics, etc. into electrical signals or sends physical quantities such as pressure, liquid level, etc. directly to the transmitter. The transmitter amplifies the weak electrical signal collected by the sensor in order to transfer or start the control element. Or a signal source that converts the non-electricity input from the sensor into an electrical signal while amplifying it for remote measurement and control.If you want to know more, you can browse (link removed by moderator) the internet.


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## splatz (May 23, 2015)

RUI said:


> Sensors and transmitters are the concept of thermal instruments. The sensor converts non-electrical physical quantities such as temperature, pressure, liquid level, material, gas characteristics, etc. into electrical signals or sends physical quantities such as pressure, liquid level, etc. directly to the transmitter. The transmitter amplifies the weak electrical signal collected by the sensor in order to transfer or start the control element. Or a signal source that converts the non-electricity input from the sensor into an electrical signal while amplifying it for remote measurement and control.If you want to know more, you can browse：*spam link snipped*



*If they don't bother to get a decent translation to English for their web site splash, what do you think the odds are the documentation is worth $0.02?  

And then the product will probably be a little worse than the documentation. *


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## paulengr (Oct 8, 2017)

The idea is that say you have a thermocouple or RTD. That’s a sensor aka transducer. But the output is nothing like a standard signal format such as 4-20 mA. A transmitter converts it into a suitable signal for transmitting to a receiver. A transmitter is not always required. You can get PLC cards that read thermocouples or RTDs or load cells for instance. And these days often the transmitter is integrated into the transducer. A lot of level sensors and flow meters output 4-20 mA directly for instance.

Transducer is a term for an electrical signal converter such as millivolts to 4-20 instead of say converting pressure into an electrical signal which is a sensor. But these two words are often used interchangeably. And since the transmitter is integrated into it too all 3 terms get used indiscriminately,


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