What is the Difference Between Transmitter and Transducer?

In telecommunications and electronics, a transmitter is an electronic device, that produces radio waves with the help of an antenna.In addition to their usage in broadcasting, these devices are necessary components in many electronic devices such as wireless computer networks, cell phones, Bluetooth enabled devices, 2-way radios in aircraft, garage door openers, spacecraft,ships, radar sets, etc. The main function of the transmitter is that it converts measurements into a signal from a sensor and sends that to control a device or display which is located at a distance away. A transducer is a device that converts a signal in one form of energy into another form. The types of energy includes electrical, chemical, mechanical, thermal and electromagnetic energy, including light. The difference between transmitter and transducer is discussed below.

Difference Between Transmitter and Transducer

Transmitters and transducers both convert one form of energy to another and give an O/P signal. The O/P signal is directed to any device that takes it and uses to alter the pressure in a system. Transmitters and transducers are almost the same thing; the main difference between a transmitter and transducer is of the electrical signal each sends. A transmitter sends an electrical signal in mA and a transducer sends an electrical signal in volts or mV.

In present days of industrial automation, the transmitters and the transducers are completely different terms. But, manufactures and research started making single package instruments that are a transducer with embedded transmitter inside.The size of single package instruments is becoming smaller due to the advancement of electronics manufacturing. Nowadays, Some transducers have ICs inside that are as small as mobile phone SIM cards.

Transmitter and transducer can be easily differentiated with their working principles as discussed in this article.

Transmitter

The transmitter is a current output device that has two or three wires. These wires are used as both transmitting and O/P signals and receive power, wherein long cables are needed. Generally, a 2-wire transmitter is used with 4-20mA output. A 3-wire transmitter has been developed to have an o/p of 0-20mA signal.

The short form of the transmitter is TX. The purpose of the transmitter is radio communication of  electronic signal over a distance. Electronic signals are video signals from a video camera, audio signals from a microphone, etc. The transmitter combines the information signal that carries with the RF signal that generates the radio waves (often called the carrier). This process is known as modulation. The information can be added to the carrier signal in different ways, in different types of transmitter such as AM transmitter and FM transmitter.

AM Transmitter:

Modulation allows low frequency audio signals to be emitted for long distances. This process is done by superimposing the low-frequency-audio signal on the high-frequency-carrier wave. The amplitude modulation transmitter is used in medium and long wave broadcasting between 153kHZ-1612kHz.

The block diagram of an AM transmitter is shown above. This AM transmitter consists of a microphone, an audio amplifier, an amplitude modulator, an RF power amplifier and radio frequency oscillator.

The microphone is used to convert sound waves into electrical signals in a range of 20 Hz-20 KHz. These electrical signals are amplified by the audio amplifier. The radio frequency oscillator generates the carrier frequency. The audio is overlaid onto the carrier by the modulator. The low power modulated carrier signal is enhanced in amplitude by the  RF power amplifier. Then, the aerial generates an electromagnetic wave, which is radiated into space.

FM Transmitter

The Frequency modulation transmitter is a low-power-Fm-radio transmitter, which broadcasts a signal from an audio device to FM radio. The block diagram of the FM transmitter is shown below. This transmitter consists of a microphone, an audio amplifier, a frequency modulated oscillator and an RF power amplifier.

The microphone is used to convert sound waves into electrical signals. These signals are amplified by the audio amplifier; the amplified audio is used to control the deviation of the frequency modulated oscillator. The oscillator frequency is at the carrier frequency. The low power of the FM carrier is enhanced by the RF power amplifier. Then, the aerial generates an electromagnetic wave.

Transducer:

The transducer is a voltage output device which is used to change one form of energy into another form, usually in millivolts (mechanical energy to electrical energy). In a process industry, 4 important and basic need to be measured and controlled – they are, flow, flow, temperature, pressure and level.

The common examples of transducer include loudspeakers, microphones,  pressure sensors, thermometers and antenna. But, the best example for transducer are stain gauge. These gauges are used for measurement of force in machine tools, stain measurement, pressure sensors, torque measurement and impact sensors. But, with the development of automation in industries like  power plants, boiler operations  and process instruments are necessary to throw the readings over long distances. The output of the transducer is in millivolts, which is needed to travel over long distances to the control rooms.

Transducers are classified into four types: ultrasonic transducers, pressure transducers, piezoelectric transducer and ultrasound transducer.The important consideration of any transducer is its efficiency. It is defined as the ratio of the power o/p in the desired form to the total power i/p. Mathematically, if the total power input is P, and the power output is Q, then the efficiency E will be

                                                      E=Q/P

The Percentage of the efficiency is represented as E%=100Q/P

Every transducer is not 100% efficient due to power loss in the process of conversion. Generally, this loss is exhibited in the form of heat. A well-designed antenna supplied with 100watts of RF power emits 80 to 90 watts in the form of an electromagnetic field and the remaining few watts are dissipated as heat in the conductors of the antenna, the object near to the antenna, and in the dielectric and feed line conductors. The worst transducers in the form of efficiency are incandescent lamps. A 100watt lamp emits a few watts in the form of visible light. Most of the remaining power is dissipated as heat and the smaller amount is emitted in the UV spectrum.

This is all about the difference between a transmitter and transducer. The two terminologies have been slowly combining with the new technologies that are being developed in the field industrial automation and controls in the particulars of process measurement.

Photo Credits:

• Transmitter and Transducer wika
• Transmitter hobbywireless
• Transducer tech-faq