Types of Analog and Digital Sensors with Applications

We frequently use different types of sensors in several electrical and electronic applications, which are classified as chemical, pressure, temperature, position, force, proximity, thermal, presence, flow, optical, automotive, sound, speed, magnetic, electric, heat, fiber-optic sensors, analog and digital sensors. A sensor can be defined as an appliance that detects changes in physical or electrical or other quantities and by this means, generally, produces an electrical or optical signal output as an acknowledgement of the change in that specific quantity. In this article, we will discuss about different types of sensors and practical examples in brief. But, primarily we must know the types of analog and digital sensors.

Analog Sensors

There are different types of sensors that produce continuous analog output signal and these sensors are considered as analog sensors. This continuous output signal produced by the analog sensors is proportional to the measurand. There are various types of analog sensors; practical examples of various types of analog sensors are as follows: accelerometers, pressure sensors, light sensors, sound sensors, temperature sensors, and so on.

Accelerometers

Analog sensors that detect changes in position, velocity, orientation, shock, vibration, and tilt by sensing motion are called as accelerometers. These analog accelerometers are again classified into different types based on the variety of configurations and sensitivities.

These accelerometers are available as analog and digital sensors, based on the output signal. Analog accelerometer produces a constant variable voltage based on the amount of acceleration applied to the accelerometer.

Light Sensors

Analog sensors that are used for detecting the amount of light striking the sensors are called as light sensors. These analog light sensors are again classified into various types such as photo-resistor, Cadmium Sulfide (CdS), and, photocell. Light dependent resistor (LDR) can be used as analog light sensor which can be used to switch on and off loads automatically based on the day light incident on the LDR. The resistance of the LDR increases with decrease in light and decreases with increase in light.

Sound Sensors

Analog sensors that are used to sense sound level are called as sound sensors. These analog sound sensors translate the amplitude of the acoustic volume of the sound into an electrical voltage for sensing sound level. This process requires some circuitry, and utilizes microcontroller along with a microphone for creating an analog output signal.

Pressure Sensor

The analog sensors that are used to measure the amount of pressure applied to a sensor are called as analog pressure sensors. Pressure sensor will produce an analog output signal that is proportional to the amount of applied pressure. These pressure sensors are used for different types of applications such as piezoelectric plates or piezoelectric sensors that are used for the generation of electric charge. These piezoelectric sensors are one type of pressure sensors that can produce an analog output voltage signal proportional to the pressure applied to the piezoelectric sensor.

Analog Temperature Sensor

Temperature sensors are widely available as both digital and analog sensors. Typically used analog temperature sensors are thermistors. There are different types of thermistors that are used for different applications. Thermistor is a thermally sensitive resistor that is used for detecting changes in temperature. If the temperature increases, then the electrical resistance of thermistor increases. Similarly, if temperature decreases, then the resistance decreases. It is used in various temperature sensor applications.

Practical example of analog temperature sensor is thermistor based temperature control system. This project is used to maintain constant temperature in an enclosed area. A block diagram of temperature control system consists of lamp (that represents a cooler), temperature sensor or thermistor, relay.

If the temperature exceeds certain value, then the lamp switches on automatically indicating a cooler for bringing back temperature to normal value. Operational along with a negative temperature coefficient thermistor is used for activating relay-in case if the temperature exceeds certain range. As this process of activating relay for switching on cooler (in this system shown as lamp) can be done automatically, hence there is no need to monitor temperature in person. Thermistor is most frequently used analog temperature sensor, because of its low cost advantage. Whenever changes occur in temperature, then the input parameters to the op-amp will be altered. Thus, op-amp delivers an output that energizes relay and the load turns on or off accordingly.

If we use a digital temperature sensor instead of analog temperature sensor, then the accuracy of temperature control system can be improved.

Digital Sensors

Electronic sensors or electrochemical sensors in which data conversion and data transmission takes place digitally are called as digital sensors. These digital sensors are replacing analog sensors as they are capable of overcoming the drawbacks of analog sensors. The digital sensor consists of majorly three components: senor, cable, and transmitter. In digital sensors, the signal measured is directly converted into digital signal output inside the digital sensor itself. And this digital signal is transmitted through cable digitally. There are different types of digital sensors that overcome disadvantages of analog sensors.

Digital Accelerometers

The method of generation of variable frequency square wave output by the digital accelerometer is called as pulse-width modulation. The readings are taken by the pulse width modulated accelerometer at fixed rate, generally at 1000 Hz (but this can be configured by a user based on the IC used). The output PWM signal, pulse width or duty cycle is proportional to the acceleration value.

Digital Temperature Sensor

DS1620 is a digital temperature sensor that provides temperature of device with 9-bit temperature readings. It acts a thermostat with its three thermal alarm outputs. If the temperature of device is greater than or equal to user defined temperature TH, then THIGH is driven high. If the temperature of the device is less than or equal to user defined temperature TL, then the TLOW is driven high. If the temperature of the device exceeds TH and remains high until it falls below that of TL, then the TCOM is driven high.

A practical example of the digital sensor can be considered as a digital temperature control system using digital temperature sensor that has more advantages and accuracy compared to the analog temperature control system using analog sensor thermistor.

Digital temperature sensor DS1620, push buttons, seven segment display, and relay are interfaced to 8051 microcontroller. This proposed digital temperature control system provides display of temperature information using seven-segment displays. If the temperature value exceeds set point, then the load (heater) gets switched off by the relay after receiving signal from the microcontroller. Here a lamp is used to represent the load for demonstration purpose. As this digital temperature control system provides accuracy by displaying temperature information on seven segment displays, it is advantageous than the analog temperature control system.

The recent emerging trends in technologies have developed most advanced digital sensors to overcome disadvantages of the analog sensors. Slowly, every analog sensor is getting replaced by the digital sensor in many applications. For more technical help regarding electronics projects using analog and digital sensors, you can contact us by posting your comments in the comments section below.

Photo Credits

• Accelerometer by amazon
• Sound Sensor by ebayimg