What is Transducer?

A transducer is an electronic device that functions to convert the energy from a certain form into another form. The process to convert the energy from one form into another is called transduction.

The conversion is going through two processes, which are sensing and transducing the physical quantity (units) such as length, pressure, temperature, sound, vibration, humidity, etc.

Like the digital caliper and digital micrometer, for example. These precision instruments generally utilize incremental capacitance transducer. The transducer turns the displacement into some electric signals. Then the ADC turns the electric signal (analog) into a digital signal and processes the reading into the LCD screen.

There is a reason why a transducer is needed. As a matter of fact, it is hard to get the exact physical quantity magnitude such as pressure and temperature. However, it is getting easier if the physical quantity is converted to an electric signal (as an example) so that it can be transmitted, processed, and shown on a display reading.

The transducer with the output signal (4-20mA is the most common to use) is a transmitter. The 4-20mA signal is robust from electrical noise and resistance in the wiring unit. It is best for long-distance transmission.

Note: Keep in mind that the practice is not always about the conversion from physical quantity into electric signals. The transducer also addresses as a device to convert an electric signal into a physical form such as what happens to your loudspeaker or headset.

Since it can convert from physical quantity into an electric signal or vice versa, talking about transducer also means talking about sensors and actuators.

Sensor Vs. Transducer

There seems to be an ambiguous understanding of sensors and transducers. Here, we attempt our best to deliver the right information for the readers. The difference between the two can be explained through the following table.

SensorTransducer
Converts physical quantities into the electrical equivalent quantities such as resistance, inductance, capacitance, etc.Does not always convert physical quantity into electrical quantity. It can convert an electric signal to physical quantities as well.
Has no signal processing. Just a stand-alone sensing function.Has signal processing such as filtering, amplification, attenuation, modulation, etc.
A sensor is a part of the transducer system.A transducer is the joint of the sensor as the sensing element and the transduction element as the conversion or signal processing element.

Transducer Vs. Actuator

An actuator is a system/machine that controls a mechanism or system such as a valve. It is an example of how some electric signal turns into physical form (motion).

Bidirectional Transducer

Bidirectional transducer does the two things in the same device. It converts physical quantities into electric signals and converts the electric signals into physical quantities as well. One of the examples is an antenna. It turns radio waves (electromagnetic waves) into electric signals as well as turns electric signals into radio waves.

Transducer Parts

It consists of two main parts as the following.

1. Sensing Element

It is the part that responds to any changes in physical features. The response is dependant on physical phenomena such as pressure change, motion change, heat change, etc.

2. Transduction Element

This part has the role to convert the sensing element response output into an electrical signal. The conversion is basically a signal processing/conditioning (filter, amplify, attenuate, modulate, etc) to produce the output in a standard electrical form such as 4-20mA, 0-10VDC, -10 to +10VDC, and 0-25mA.

To sum, the overall process going on inside the transducer can be described by the illustration below.

Tranducer Working Flow

Classification

a. based on the energy source

It can be classified based on the energy source into two groups in the following table.

ActivePassive
Self-generating under the energy conversion principle.Not self-generating under the energy controlling principle.
Produce the output in electric potential or current.Produce the output in the change of resistance, inductance, or capacitance.
Not require the external power (excitation) source.Require the external power source.
Such as thermocouple, piezoelectric, pyroelectric transducer, etc.Such as RTD, thermistor, potentiometer, etc.

b. based on the transduction principle

There is another method to classify based on the transduction principle. It can be primary and secondary transducer. A primary transducer will convert the physical quantity to displacement and mechanical motion such as the diaphragm, Bourdon Tube, Bellows, etc. While the secondary will convert the physical quantity to the electrical signals such as current, voltage, resistance, inductance, capacitance change, etc. The devices could be LVDT, Piezoelectric sensor, thermocouple, RTD, etc.

c. based on the physical quantity

The physical quantity can be used it is the main material that will be converted at the last stage of the transducer system. The examples of the said transducers include the following.

  1. Temperature transducer such as a thermocouple
  2. Flow transducer such as flowmeter
  3. Pressure transducer such as Bourdon Gauge

d. based on the output signals

The output signals of the transducers could be discrete or continuous. The analog transducer will produce continuous output signals. The examples include a thermocouple, LVDT, thermistor, and strain gauge. On the other hand, the digital transducer will produce discrete output signals that mainly work on high or low power. Examples of digital types are digital tachometers, Hall Effect Sensors, shaft encoders, and limit switches.

Characteristics

There are static and dynamic characteristics.

The static means that the characteristics change constantly with time or mostly constant and do not differ. Therefore, the statics are precision, resolution, sensitivity, linearity, drift, span, noise, accuracy, stability, repeatability, responsiveness, and input-output impedances.

While the dynamic means the characteristics changes quickly as a function of time. Therefore, the dynamic includes fidelity, bandwidth, response speed, and dynamic error.

Types and Applications

The types can be categorized depending on the operation principle as below.

1. Pressure Transducer

It is the transducer kind that converts the applied pressure into electrical signals. In its application, we could find it mostly to measure the specific pressure of water, air, gas, or liquid by changing the pressure into electrical energy. Below is the sample of the water pressure transducer by Walfront.

2. Ultrasonic Transducer

It is the type that converts the electrical signals to ultrasound waves. A simple example is HC-SR04 that is mostly used to measure a distance based on the reflection.

3. Piezoelectric Transducer

It is the transducer type that converts the applied mechanical stress (energy) into electrical energy. In a similar way, it also makes electrical energy converts into mechanical energy. That said, it can be found in electronic drum pads to detect the stick drummer impact and the muscle movement in the acceleromyograph. The following is the piezoelectric product by the Uxcell brand.

4. Temperature Transducer

This is the type that converts the temperature into other energy forms such as electrical, pressure, or mechanical energy. This kind of transducer is often used to measure the temperature in HVAC (Heating, Ventilation, and Air-conditioning) field. Below is a thermocouple as the temperature transducer for boilers, gas furnaces, or water heaters by Honeywell.

Conclusion

We may not realize the fact that we use transducers in most of our daily lives. Whether it includes our daily needs or the industrial requirements.

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