How to accurately measure body temperature?

How to accurately measure body temperature?

How to accurately measure body temperature?

Measuring body temperature is one of the most important measurements with a lot of applications in physiological studies as well as clinical research. With the advancement in technology, in recent years, numerous observations have been reported and various methods of measurement have been employed. Continuous monitoring of physiological signals could help to detect and diagnose several cardiovascular, neurological and pulmonary diseases at their early onset. Some types of temperature measurement device are mentioned below:

Thermocouple: or sometimes called as TC is one of the most widely used temperature sensors in manufacturing, machining, and scientific applications. The sensor has the advantage of being robustness, low-cost, and self-powered. Such features have made them a good choice for long-distance applications.

Temperature Sensor

Resistance Temperature Detector (RTD):

In a resistor temperature detector, the resistance is proportional to the temperature. The main metals used in these sensors include Ni (Nickle), Pt (platinum) and Cu (copper). This resistor is capable of making a wide range of temperature measurement as it can be used to measure temperature in the range between -270 0C to +850 0C. However, the current produces heat in a resistive element causing an error in the temperature measurements. PT100 and PT1000 are famous RTD sensors.

PT100- temperature sensor

Thermistor:  

This is another type of temperature sensor and its name is the acronym of “thermally sensitive resistor”. This sensor is relatively low cost, flexible, and easy to use. This sensor works based on changing its resistance in response to temperature. It was first discovered by Michael Faraday back in 1833 but was manufactured after 1933.

s-l300- temperature sensor

Max 30205:

This temperature sensor is a product of Maxim and accurately measures body temperature with an accuracy of 0.1oC. It is also capable of providing an over temperature alarm/interrupt/shutdown output. It is available in an 8-pin TDFN package and can operate over a reasonable range of temperature from 0°C to +50°C.

MAX30205- temperature sensor

Other temperature sensors:

Besides the above-mentioned measuring devices, there are some wearable sensors available for measuring body temperature.

One of these sensors works by integration of optical fiber Bragg grating (FBG)-based sensors into functional textiles to extend the capabilities of wearable solutions for body temperature monitoring. In addition, the temperature sensitivity is 150 pm/°C, which is almost 15 times higher than that of a bare FBG. This is the most used wearable design.

Another most common design for measuring body temperature for wearable application is using LMT70. This sensor is a high Precision Analog Temperature Sensor with a precision of 0.1oC.

LMT70- temperature sensor

LMT70 has two parts, wearable design part, and an electrical design part. The Wearable Design section includes an overview of the electrical and mechanical design of the LMT70 Wearable Design. For making an accurate measurement, the mechanical aspects of the design should be carefully considered to conduct all the heat possible into the LMT70.   

The electrical design is composed of two PCB’s:

  1. The main PCB board which includes such components as the battery, LCD connector, the ADS1115, and the MSP430G2553 is responsible for converting the LMT70 data into an accurate temperature value.
  2. The remote PCB which is a very small PCB that includes LMT70 which is a body temperature sensor. In addition to this component, such supporting thermal devices as copper pads and thermal vias are used also to sense skin temperature. These two boards are connected to each other.

Conclusion:

There are various methods available for measuring the temperature of the body. But the best method is the use of wearable sensors which are being progressively more comfortable and less obtrusive. The advancement in low-power, compact wearables (sensors, actuators, antennas, smart textiles), inexpensive computing and storage devices coupled with modern communication technologies pave the way for low-cost, unobtrusive, and long-term health monitoring system.

References:

https://www.omega.com/prodinfo/thermistor.html

http://www.ti.com/product/LMT70

https://www.mikroe.com/fever-click

https://www.thomasnet.com/articles/automation-electronics/Thermocouples-Types/

http://www.thermo-kinetics.com/resistance-temperature-detectors

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