Transducer and Sensor

Overview

All energy forms are convertible with the help of transducers. The method of conversion is referred to as transduction. We find the application of transducers in automation technology where machines reduce human interventions to a great extent. Whether it be the measurement of large volumes of input energy in manufacturing plants or simple automated banking operations, transducers save time and eliminate the risk of errors. Modern measuring devices use them to ensure accurate results and engineers rely on them. To manage the operation of electronic devices transducers are used in control loops. The control loops or systems establish a set point against which the automated processes are monitored and regulated through feedback generation. Transducers are categorized based on the nature of conversion they are being used for. For example, the ones that convert physical displacement into electrical quantities are termed electrical transducers. A sensor is a form of transducer that reacts to stimuli from only physical systems. Automated telemetries that are used for collecting measurements on-site, use sensors to receive signals. 

Types of Transducers 

Before jumping into elaborate classification, we must understand that the transducers can be broadly classified into two categories: input transducers, also known as sensors and the actuators output transducers. Microphones exhibit the conversion of sound waves into readable electrical signals, here we find the application of sensors. On the contrary, if we study the operation of motors, we can see how the actuators work oppositely. In motors, actuators convert electricity into physical motion. Now let us take a brief look at the various types of transducers:

Magnetic field transducer: When a ferrous object approaches the magnetic field, these transducers convert the magnetic flux inside the field into electrical signals at terminals of the coil. 

Pressure transducers: They are used to measure the force of fluids and produce a measurable electrical output. Pressure transducers help us to assess the pressure (force per unit area) limit beyond which the liquid or gas will start swelling. They are also known as load cells. 

Current transducer: These are used to measure the industrial standard signal output from a primary AC source. The output is expressed in voltage. 

Active induction transducer: They possess two coils. The first one causes excitation while the second coil gives the output. Thus, the mutual induction generates voltage differences that depend on the armature motion. 

Electromechanical transducer: Any form of electrical appliance that can convert electrical signals into sound waves and vice versa, for example, speakers, microphones, etc. are considered to be built with electromechanical transducers. A very small amount of input power is needed to operate these transducers. LVDT transducer is an example of an electromechanical transducer. 

Electroacoustic transducer: Commonly referred to as piezoelectric transducers, they are capable of transforming pressure or stress generated on a solid metal into electrical output signals. In this case, there is no mechanism to measure the output. 

Thermocouples: These devices measure temperature using a couple of wires made of different metals. The wires are connected at opposite ends of the device. The input energy is fed by joining one wire to the temperature source while the second wire remains connected with a comparatively lower temperature. Thermocouples find their application inside gas furnaces. 

Strain gauges: These transducers when mounted on a body produces measurable electrical output from strain generated on that body. The cause of strain is a physical phenomenon of load or displacement. 

Parts of a Transducer

To detect the changes in the surrounding physical world, transducers are provided with a sensor head. This part interacts with the environment to return electrical signals as output. The environmental changes may arise from fluctuating temperature, pressure, electromagnetic field, etc. After the detection phase, the conversion begins which presents the need for electronics. This can be a form of resistor that helps in checking induced current and converting it into an output voltage. Amplifiers also work on a similar principle by resonating very minute electrical signals. 

Active and Passive Transducers 

Active transducers do not require an external source of energy like passive transducers. Also, the inductance and resistance of passive transducers get affected after input energy is passed which is unlikely for active transducers. A differential transformer is a form of the passive transducer. A complicated design is cited for passive transducers. Simplified photovoltaic cells and thermocouples are identical examples of active transducers. 

Transducers and Sensors: Difference

1. Transducers facilitate energy conversion to various forms. Sensors provide output electrical signals from input non-electrical energy. The signals are measurable. 
2. Though used synonymously, Americans prefer to call transducers in modern-day machines and gadgets as sensors. 
3. Resistance in transducers changes when there is a discrepancy in voltage. In sensors, resistance change depends on the change in temperature, load, humidity, etc. 
4. A sensor must be connected to a bridge circuit to be called a transducer. Therefore, we can conclude that all transducers are sensors but vice versa is not true as sensors only convert non-electrical energy into an electrical signal. 

Conclusion

Transducers are a part of circuitry where they convert various forms of energy into their corresponding alternatives. On the other hand, sensors can only produce electrical signal output from various physical parameters that are fed as input. A temperature sensor cannot be considered as a transducer although it converts thermal energy into electrical energy because it is not a part of any bridge circuit. Some examples of transducers are piezoelectric transducers, electromagnetic transducers, strain gauges, etc.