Analog and Digital Sensors:Types and Applications

We often use a variety of sensors in many electrical and electronic applications. These sensors are categorized 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 a device that detects changes in physical, electrical, or other quantities and typically produces an electrical or optical signal output in response to the change in the specific quantity. In this article, we will briefly discuss different types of sensors and practical examples. However, it is essential first to understand the types of analog and digital sensors.

Analog Sensors

Some sensors generate a continuous analog output signal and are known as analog sensors. This continuous output signal is proportional to the measured quantity. Examples of various types of analog sensors include accelerometers, pressure sensors, light sensors, sound sensors, temperature sensors, and others.

Accelerometers

Analog sensors that detect changes in position, velocity, orientation, shock, vibration, and tilt by sensing motion are referred to as accelerometers. These analog accelerometers can be further classified into different types based on various configurations and sensitivities.

Accelerometers can be categorized as analog and digital sensors depending on the type of output signal they generate. An analog accelerometer produces a continuous variable voltage corresponding to the amount of acceleration applied to it.

Light Sensors

Analog sensors used to detect the amount of light hitting the sensors are known as light sensors. These analog light sensors can be further classified into different types, such as photo-resistor, Cadmium Sulfide (CdS), and photocell. A light dependent resistor (LDR) can serve as an analog light sensor, automatically switching loads on and off based on the daylight incident on the LDR. The resistance of the LDR increases as the light decreases and decreases as the light increases.

Analog Sound Sensor

Analog sensors used to detect sound levels are known as sound sensors. These analog sound sensors convert the amplitude of the acoustic volume of sound into an electrical voltage to sense the sound level. This process involves some circuitry and uses a microcontroller along with a microphone to generate an analog output signal.

Pressure Sensor

Analog sensors used to measure the amount of pressure applied to them are known as analog pressure sensors. These sensors produce an analog output signal proportional to the applied pressure. They are used in various applications, such as in piezoelectric plates or piezoelectric sensors, which generate an electric charge. Piezoelectric sensors are a type of pressure sensor that can produce an analog output voltage signal corresponding to the pressure exerted on them.

Analog sensors used to measure the amount of pressure applied to them are known as analog pressure sensors. These sensors produce an analog output signal proportional to the applied pressure. They are utilized in various applications, such as piezoelectric plates or piezoelectric sensors, which generate electric charges. Piezoelectric sensors are a type of pressure sensor that can produce an analog output voltage signal corresponding to the pressure exerted on them.

Analog Temperature Sensor

Temperature sensors are commonly available as both digital and analog sensors. A widely used type of analog temperature sensor is the thermistor. There are various types of thermistors, each suited for different applications. A thermistor is a thermally sensitive resistor that detects changes in temperature. As the temperature increases, the electrical resistance of the thermistor increases, and as the temperature decreases, the resistance decreases. Thermistors are used in a variety of temperature sensor applications.

A practical example of an analog temperature sensor is a thermistor-based temperature control system. This system is used to maintain a constant temperature in an enclosed area. The block diagram of a temperature control system includes a lamp (representing a cooler), a temperature sensor or thermistor, and a relay.

When the temperature exceeds a certain value, the lamp automatically switches on, indicating the activation of a cooler to restore the temperature to normal. An operational amplifier, along with a negative temperature coefficient thermistor, is used to activate the relay if the temperature goes beyond a specific range. Since the process of activating the relay to turn on the cooler (represented as a lamp in this system) is automated, there is no need for manual temperature monitoring. The thermistor is commonly used as an analog temperature sensor due to its low cost. When temperature changes occur, the input parameters to the op-amp are altered, causing the op-amp to deliver an output that energizes the relay, thereby turning the load on or off as needed.

If a digital temperature sensor is used instead of an analog temperature sensor, the accuracy of the temperature control system can be improved.

Digital Sensors

Electronic or electrochemical sensors that perform data conversion and transmission digitally are known as digital sensors. These sensors are gradually replacing analog sensors because they can overcome the limitations of analog sensors. A digital sensor typically consists of three main components: the sensor, the cable, and the transmitter. In digital sensors, the measured signal is directly converted into a digital output signal within the sensor itself. This digital signal is then transmitted digitally through the cable. There are various types of digital sensors that address the drawbacks of analog sensors.

Digital Accelerometers

The process used by a digital accelerometer to generate a variable frequency square wave output is known as pulse-width modulation. Readings are taken by the pulse-width modulated accelerometer at a fixed rate, usually 1000 Hz (though this rate can be adjusted by the user depending on the IC used). The output PWM signal, including the pulse width or duty cycle, is proportional to the acceleration value.

Digital Temperature Sensor

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

A practical example of a digital sensor is a digital temperature control system that uses a digital temperature sensor. This system offers greater advantages and accuracy compared to an analog temperature control system using an analog sensor thermistor.

The digital temperature sensor DS1620, push buttons, seven-segment display, and relay are interfaced with the 8051 microcontroller. This proposed digital temperature control system displays temperature information using seven-segment displays. If the temperature value exceeds the set point, the relay switches off the load (heater) after receiving a signal from the microcontroller. For demonstration purposes, a lamp is used to represent the load. This digital temperature control system offers greater accuracy by displaying temperature information on the seven-segment displays, making it more advantageous than an analog temperature control system.

Recent technological advancements have led to the development of highly advanced digital sensors that address the drawbacks of analog sensors. Gradually, digital sensors are replacing analog sensors in many applications. For further technical assistance with electronics projects involving analog and digital sensors, you can reach out by posting your comments in the comments section below.

Related Articles

What are Proximity Sensors ?

IR Sensors: Schematic and Priciple Explained

How Do Motion Sensors Work? Types & Applications