SENSORS AND TRANSDUCERS

Sensors and transducers are input and output devices, respectively, that can be incorporated into an electronic circuit or system to measure or change the environment. However, for an electronic circuit or system to perform a useful task or function, it must be able to communicate with the "real world", either by reading an input signal from an ON/OFF switch or by activating it in some way. output a device for illuminating a single light.

In other words, an electronic system or circuit must be able to "do" something, and sensors and transducers are the perfect components to do it. The word "transducer" is a general term used for both sensors that can be used for various forms of energy, such as motion, electrical signals, radiant energy, thermal or magnetic energy, and actuators that can be used to change. voltage or current.

There are many different types of sensors and transducers to choose from, both analog and digital, input and output. The type of input or output transducer used really depends on the type of signal or process being "sensed" or "controlled", but we can define sensor and transducers as devices that convert one physical quantity into another.

Devices that perform an "input" function are generally called sensors because they "detect" physical changes in some characteristic that changes in response to some excitation, such as heat or force, and mask them with an electrical signal. Devices that perform the "Output" function are generally called actuators and are used to control some external device such as motion or sound.

Electrical transducers are used to convert one type of energy into another type of energy, for example, a microphone (input device) converts sound waves into electrical signals for amplification by an amplifier (process), and a speaker (input device) output) converts these electrical signals. signals back into sound waves. There are many different types of sensors and transducers on the market and the choice of which one to use really depends on the quantity being measured or controlled and the most common types are listed in the table below:

Input-type transducers or sensors produce a voltage or signal output response proportional to the change in its measured quantity (stimulus). The type or amount of output signal depends on the type of sensor used. However, generally, all types of sensors can be divided into two types: passive or active sensors. In general, active sensors require an external power source to operate, called a drive signal, which the sensor uses to generate an output signal. Active sensors are self-generating devices in which their properties change in response to an external stimulus to produce, for example, an output voltage of 1 to 10 V DC or an output current such as 4 to 20 mA DC. Active sensors can also amplify the signal.

A good example of an active sensor is an LVDT sensor or strain gauge. Strain gauges are pressure-sensitive resistive bridge networks that are externally biased (excitation signal) so that the output voltage is proportional to the amount of force and/or voltage applied to the sensor.

Analogue sensors
Analogue sensors produce a continuous output signal or voltage that is usually proportional to the quantity being measured. Physical quantities such as temperature, velocity, pressure, displacement, stress, etc. are analogous quantities because they are generally constant. For example, the temperature of a liquid can be measured with a thermometer or thermocouple that continually responds to changes in temperature as the liquid heats up or cools down.

Analogue sensors tend to generate output signals that vary smoothly and continuously with time. These signals are typically very small, from a few microvolts (UV) to a few millivolts (mV), so some amplification is required. Circuits that measure analogue signals often have a slow response and/or low accuracy. Analogue signals can also be easily converted to digital signals for use in microcontroller systems using analogue-to-digital converters, or ADCs.

Digital sensors
As the name suggests, digital sensors produce discrete digital output signals or voltages that are a digital representation of the quantity being measured. Digital sensors produce a binary output signal in the form of a logic "1" or a logic "0" ("ON" or "OFF"). This means that a digital signal produces only discrete (continuous) values that can be output as a single "bit" (serial transmission) or by combining bits to produce a single "byte" output (serial transmission).