What is a temperature sensor that can be used in IoT?

With the progress of IoT-related technology, the value of temperature sensors is being reassessed, but why is that?

This article is intended for those who are not familiar with temperature sensors, and explains why temperature sensors are attracting renewed interest in IoT and how to select a temperature sensor.

A comparison of the temperature sensors provided by each manufacturer is also posted, so it would be greatly appreciated if you could use it as an aid in sensor selection.

Why temperature sensors are attracting attention in IoT

There are various types of sensors, but temperature sensors have a relatively long history among many sensors.

Therefore, temperature sensor technology is mature, and simple temperature sensors can be purchased at very low prices.

Humans see and feel that someone has crossed in front of them.

However, if you have a temperature sensor, you can also feel the heat.

In general, temperature sensors are cheaper than optical sensors, so it makes sense from a cost standpoint to use temperature sensors as motion sensors for automatic doors.

Living things aren’t the only things that generate heat.

Various things around us, such as electronic circuits and industrial machines, transmit information through heat.

A temperature sensor is a very effective device for collecting and utilizing such information as inexpensively and in large quantities as possible.

In other words, one of the reasons for the reevaluation of temperature sensors was that they matched the IoT requirements of “installing a large number of sensors and utilizing big data.”

Specific examples of temperature sensor utilization in IoT

Temperature sensors are used in various applications other than automatic doors.

Let’s look at some specific examples in order to have an image of IoT-like utilization of temperature sensors.

Refrigerator temperature control

Refrigerator temperature control and recording are necessary in the food manufacturing field, which requires strict hygiene and quality control.

Temperature sensors and IoT automate the temperature check work that has been done visually by humans, contributing to work cost reduction.

Air conditioning management

Especially in large facilities and factories, the annual electricity bill for air conditioning is enormous.

By linking the temperature information obtained by the temperature sensors and the location information of each sensor with the air conditioning system, it is possible to efficiently spread warm and cold air and reduce electricity costs.

Chemical plant piping temperature control

Cracks are likely to occur in tanks and piping in chemical plants that handle highly corrosive chemicals and high-temperature raw materials.

By monitoring and analyzing temperature changes when failures or accidents occur, signs of accidents can be detected and used to prevent accidents.

In addition, it is possible to reduce the burden on workers required for piping check work.

Points for choosing a temperature sensor

Below, we will explain how to select a temperature sensor.

It is not possible to decide on a single temperature sensor just by determining the purpose and application.

Pay attention to the following three points when selecting a temperature sensor.

Withstand temperature range

The temperature range in which a temperature sensor can withstand use differs depending on the type.

Temperature sensors that use semiconductors are not particularly suitable for places where large amounts of heat are generated, such as factories.

If you use it at an inappropriate temperature, it will not be able to demonstrate its potential specs and will cause failure.

Required accuracy

Sometimes a 1°C difference in temperature doesn’t matter too much, and sometimes a 0.1°C difference is significant.

An unnecessarily high-spec sensor puts pressure on the price, so choose a sensor that meets the required accuracy.

Price

Especially if you want to handle big data with IoT, the price of each sensor will eventually make a big difference.

If there are a large number of sensors, there is a possibility that costs will increase due to malfunctions and maintenance inspections, so be careful about the balance between specifications and price.

Types and mechanisms of temperature sensors used in IoT

There are many types of temperature sensors, each with different mechanisms and characteristics.

Once you have decided on the temperature range, required accuracy, and price range for which the temperature sensor will be used, let’s decide on the “type of temperature sensor” based on these.

As an old temperature sensor, there is one that uses the volume expansion of mercury, but it is not suitable for IoT utilization because it cannot output as an electrical signal.

When used for IoT, the output is mostly limited to electrical signals.

Below, we will explain the types of temperature sensors that can be used for IoT and the mechanism of each temperature sensor.

Contact temperature sensor

A contact-type temperature sensor, like a thermometer or thermometer, is a temperature sensor that is used by directly contacting the object (human body or air) whose temperature you want to measure.

There are four main types used in IoT: resistance temperature detectors, thermistors, thermocouples, and IC temperature sensors.

RTD

The resistance of metals is not constant.

In general, the resistance of metals is characterized by being large at low temperatures (current does not flow easily) and low at high temperatures (current flows easily).

A “resistance temperature detector” uses this property to calculate the temperature from the current value.

Various metals are used, but platinum (Pt) is the most commonly used.

Platinum resistance thermometers can measure temperatures with high accuracy and can be used from high temperatures of 600°C to extremely low temperatures (-200°C).

Because it uses precious metal, it is a little more expensive than other temperature sensors.

Thermistor

A thermistor is a temperature sensor that uses semiconductors or ceramics instead of metals.

The basic principle is the same as the resistance thermometer, using resistance change due to temperature.

Resistance temperature detectors have a constant resistance change over the entire temperature range when the temperature rises by 1°C, but thermistors have a sudden change in resistance at a specific temperature.

This enables more precise temperature measurement than a resistance thermometer in a specific temperature range.

Although it is inexpensive, the temperature range that can be used is limited (about -50°C to 150°C).

Thermocouple

A thermocouple is an element with a simple structure in which two different types of metal conductors are connected to form a circuit.

However, the principle of temperature measurement is a bit difficult, so I will omit it here (search for “Seebeck effect” for details).

Like RTDs, they can cover a wide temperature range and, in addition, they do not require the use of high-grade metals, so they can be purchased at a relatively low cost.

IC temperature sensor

An IC (integrated circuit) temperature sensor is an element that integrates various thermistors, reference voltage sources, amplifiers, etc.

It compensates for the thermistor’s drawback (which is also an advantage) of high sensitivity at a specific temperature, and exhibits a constant current change over a wide temperature range.

Non-contact temperature sensor

A non-contact temperature sensor is a sensor that can measure the temperature of the object to be measured from a distance, like a motion sensor on an automatic door.

Almost all substances in nature emit invisible light called “infrared”, and the energy of this infrared is related to the temperature of the radiation source.

A non-contact temperature sensor measures the temperature of an object by measuring this infrared energy.

Because it is non-contact, it is possible to measure temperatures at which most solids melt (about 1500°C).

Comparison of temperature sensors from different companies

Based on the above, let’s compare the products handled by temperature sensor manufacturers.

Sheathed thermocouple (Nagoya Scientific Instruments)

Nagoya Kagaku Kiki sells various types of temperature sensors (injection type, stick type, magnet type, etc.) centering on thermocouples.

We also manufacture made-to-order products other than standard products according to the application.

Thermistor sensor (SEMITEC)

SEMITEC sells thermistors for various applications such as OA equipment, automotive, medical, and home appliances.

If you need a lot of sensors cheaply, this is recommended.

SHT3x series (SENSIRION)

The “SHT3x series”, which uses an IC temperature sensor, is equipped not only with a thermometer but also with a hygrometer, and is characterized by its high reliability that allows it to operate even in high-humidity environments.

From low-cost to high-end versions, it can be used for various applications.

Since the signal processing function is also implemented, communication with the outside is easy. It is the best sensor for making several prototypes.

Summary

Thank you for reading this far.

There is a wide variety of temperature sensors, and it is difficult to decide which manufacturer to use.

However, there is no doubt that it will be easier to select a sensor that meets the purpose and application of your company if you return to its principles and characteristics.

By extracting your company’s requirements from three points (temperature range, accuracy, price) and determining the type of sensor (thermistor, thermocouple, etc.), you can narrow down the manufacturers to investigate.

If you are unsure about which temperature sensor to use for IoT, first think about what your company wants to do, and be conscious of selecting a sensor that meets that purpose.