FEATURE SENSORS & SENSING SYSTEMS


Mehrdad Peyvan, application manager at Analog Devices, discusses how to choose the right temperature sensor, looking into their advantages and disadvantages, as


cutting-edge sensor advancements


A


n essential component in applications ranging from consumer electronics to industrial processing, selecting the correct


temperature sensor is essential in order to guarantee precise and accurate temperature recordings. This, however, can be a challenge considering the variety available. When specifying a sensor, there are a number of factors that need to be considered: Temperature range, accuracy, power consumption, size limitation, communication protocol (SMBus, SPI, I2


C, 1-Wire, etc.), and


budget. Each of these requirements helps narrow down the selection of the most appropriate device.


TEMPERATURE SENSOR TYPES Technically, the most popular four categories of temperature sensors available are: • RTD (resistance temperature detector): RTDs offer excellent accuracy and stability over a moderate temperature range (-200˚C to +850˚C). If precision is the priority, an RTD is the right choice. • Thermocouple: If a wide range of temperature measurements is required for an application, thermocouples are generally used. While their accuracy at high temperatures (-270˚C to +1800˚C) is low, they are the appropriate choice for low temperature situations. • Thermistor: Thermistors are cost-effective and generally used in consumer electronics. They offer relatively good accuracy over a limited temperature range (-270˚C to +1800˚C). • Diode-based sensor: Diode-based sensors utilise the voltage drop across a diode vs. the temperature. They are cost-effective and have limited temperature measurement (-55˚C to +150˚C), have fast response time, and are smaller than the other three types. Diode-based temperature sensors can be easily interfaced with a microcontroller, ADC, and


44 DESIGN SOLUTIONS MAY 2025


SENSOR SENSE: CHOOSING SENSOR FOR YO


well as developments that are driving


Figure 1. A typical MAX31888 application circuit


ASICS. They have a wide range of applications – from consumer electronics, industrial automation, data centres (storage systems), and automotive, to many other diverse electronic applications.


COMMUNICATION The output of a temperature sensor can be an analogue voltage or digital signal. Modern temperature sensors use digital communication such as SMBus, SPI, I2


C, and 1-Wire


interfaces, offering simple communication with microcontrollers and other digital devices. A 1-Wire interface allows multiple sensors to be connected to a single data line.


ACCURACY Choosing a temperature sensor that is accurate is essential, especially for applications that require exact temperature readings. To achieve this, an RTD or a diode-based temperature sensor using calibration should be chosen. Table 1 shows a list of the latest, most accurate, ADI temperature sensors with their communication interface and package.


An example of a very accurate temperature sensor, the MAX31888, is shown in Figure 1. It’s a 1-Wire high precision, low power digital temperature sensor with stunning ±0.25˚C accuracy from -20˚C to +105˚C for precision temperature monitoring. The IC consumes 68µA


“Investing time and


effort when specifying the right temperature sensor upfront can lead to improved performance, efficiency, and


cost-effectiveness in the long run”


operating current during measurement and has 16-bit resolution (0.005˚C). The sensor communicates with a microcontroller over a 1-Wire bus that requires only one data line (and a ground reference) for communication. In addition, the sensor can derive power directly from the data line through parasite power, eliminating the need for an external power supply. The


MAX31888 is available in a 6-lead µDFN package. The power supply voltage ranges from 1.7V to 3.6V for external power supplies. The operating temperature range is from –40˚C to +125˚C.


Table 1. Accuracy of the latest temperature sensors


POWER CONSUMPTION AND SIZE In battery-operated devices such as wearables, power consumption and size (they go hand in hand) are the key factors for choosing the lowest supply current and smallest device. Low power


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