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Temperature is a measure of the ability of a subject, substance, or physical system in general – to transfer heat energy to another physical system. Sensors and sensing devices are used to detect this “movement” of heat in the physical environment, also known as temperature variation. Different specialized sensor technologies are used for monitoring regular features of equipment or environments, and to detect the irregularities within these applications.

General introduction to temperature measurement

Measurement of temperature is critical especially in modern mechanical, electronic applications, and general processes. There is an increasing number of applications where detections as precise as a few millikelvins are of the essence. This enables the necessary precise decision-making functionality, simple process control of those applications, and/or avoiding the unacceptable errors.

Specifically, temperature measurement is of utmost importance within various domains such as building steel and petrochemicals, industrial applications (for process control, for triggering preventive and predictive maintenance tasks), healthcare and medical research (continuous temperature monitoring), as well as smart construction, smart agriculture, and smart consumer goods.

Essentially, temperature is a measure of the ability of a subject, substance, or physical system in general – to transfer heat energy to another physical system

By definition – in a context of a mechanical application – temperature variation in the mechanical parts is the “movement” of heat in the physical environment for various reasons (Normality: standard heat of an electric motor that is properly managed by its cooler, Abnormal: Due to improper lubrication, bearing failure, extra workload – overheating of the system).

In most of the above-mentioned applications (industrial, commercial, etc.), the measurement point is frequently far away from the indication or control point of the sensors. Such applications are unsuitable for using direct indicating standard thermometers, these require high precision Temperature Measurement Systems (mostly there are also requirements for these systems to be wireless).

These devices are usually meant to convert temperature into another form, an electrical signal, for example – to be able to detect the needed data. Temperature sensors like resistance temperature detectors (RTDs), thermistors, thermocouples, LM35, etc. are a standard choice for these applications. These sensors have the ability to measure temperature through sensing in diverse environments.

Conventionally or Commercially Available Temperature Sensors

The following types of sensors are more commonly used for temperature measurements:

  • thermistors,
  • thermocouples,
  • resistance temperature devices (RTD),
  • infrared thermometers (these are rather common in the non-contact temperature measurement sensors industry and are subdivided into spot and area measurement devices).

Most of these sensors require contact between the sensor and the subject of measurement, and some, non-contact ones are compromised by the physical environment(dust, emissivity, etc)

Thermistors

The temperature range of these sensors varies from −100 to 300 °C, the accuracy is moderate ranging in between 0.1 to 1.5 °C, has a rather low cost, and isn’t complicated to implement. Additionally are rather small – the diameter being 0.4 – 2.5 mm. Thermistors may be found in everyday appliances: fire alarms, ovens, refrigerators, digital thermometers, in many automotive applications to measure temperature, etc. However, there are some disadvantages coming with these sensors as well: non-linearity; limited range; self-heating; current source required; fragility, etc.

Thermocouples

These are known for their ruggedness, self-powered quality, wide temperature ranges (-270 – 2300 °C). Thermocouples are widely used in applications from home appliances to industrials (temperature measurement for kilns, gas turbine exhaust, diesel engines, and other industrial processes), etc. At the same time, it comes with some limitations such as lower accuracy levels (0.5 to 5 °C), low sensitivity/sta­bility, the necessity for contact, etc.

Infrared Thermometer

One of the main advantages of IR thermometers is that they detect the thermal radiant power, which is emitted by the measurement subject and the surrounding surface. This means that there is no contact necessary between the actual device and the measurement subject. These are fast responses; provide good stability; repeatability; no oxidation impact; temperature measurement range of −40 to 3 000 °C.

Due to the above-mentioned advantages, these sensors are used in applications such as heating and air conditioning (to detect insulation breakdown, heat loss/gain, furnace/duct leakage, industrial/elec­trical – to monitor motor/engine cooling systems performance, boiler operations, steam systems and detection of hot spots in electrical systems and panels, etc – you can read more about it in this article).

Some of the disadvantages associated with these sensors are the low accuracy (±2 °C); being easily compromised by the physical environment difficulties such as smoke, dust, radiation, emissivity as such; at the same time, these come with relatively complicated electronics, higher costs, and viewing size restrictions.

Other temperature sensors

There are other sensors, temperature measurement devices, HT measurement methods as well, that are used less frequently, due to various reasons, the most common ones being the niche purposes (applications) they serve (i.e. thermopiles and piezoelectric temperature sensors, bimetallic, chemical molecular change, etc.)

After days of web-surfing, it is still difficult to imagine, with all the capabilities, accuracies, and strengths, that the conventional sensors, or more accurately – any one conventional sensor, can satisfy temperature monitoring needs in accordance with the volatile market demand. Should the requirements change slightly (the budget, the accuracy needs, the dimension needs, the non-contact necessity, the stability, etc.) – the customer needs to employ a different, or additional temperature sensor.

There is a clear gap in the market for a solution that can satisfy the merged needs of the industries in need of temperature measurement, as there currently no conventionally introduced unit that can simultaneously provide the advantages such as contactless(wi­reless) sensing, resistance, stability, accuracy, cost-effectivity, miniature dimensions in the scales that would be at least acceptable.

Of course, when there is a gap within the available scientifically-backed solutions to solve this “merging issue”, the first instinct should be to outsource some Research & Development capacity. And it is for this reason that there are so many new devices coming up in the Temperature Sensor industry. The industry as such is growing vigorously, with an estimation to reach USD 8.8 billion by 2027, growing at a Compound Annual Growth Rate of 4.8 % during 2020–2027.

The only issue here is that the newly-created devices are based on the already available sensing solutions. Sure, they have improvements in design, connectivity, etc, however, these are usually the same sensors, or a combination of multiple of these same sensors made into a new device to serve, again, a niche application.

And how about the R&D that employs fundamentally new sensing principles?

A relatively young startup from Slovakia seems to have created a unique sensor that just might have solved the “merging issue” within the temperature monitoring industry.

RVmagnetics introduces the MicroWire, which is the smallest passive sensor in the world. The MicroWire sensor acts as a wireless temperature sensor is as thin and elastic as human hair (diameter of 3–70 µm and length of 1 cm – 4 cm), that can be placed directly on the subject providing real-time, contactless (no wiring needed) measurements within up to 10 cm distance.

Being a Research & Development Sensor company, RVmagnetics, essentially offering a customized alternative sensor based on magnetic principles, able to measure temperature down to 0,01 °C resolution, covering the range from –273 °C up to 600 °C. RVmagnetics custom develops the MicroWire and the sensing system for a specific application, thus meeting the demand of each customer specifically (the physical design of the final device is not framed either, as it can be a handheld device for random measurements or an attached device for constant measurements).

The solution has mostly been capitalized on within the composite monitoring, rechargeable battery monitoring, electric motor maintenance, and many more industrial sectors, earning intense involvement and positive feedback in the E-mobility, Automotive, Oil&GAs, Energy, Preventive/Pre­dictive Maintenance, MedTech industries.