WBGT

Pseudo WBGT Feeling Temperature Measurement

Fig. Measurement Environment

Supported Target MCU Devices

Supported Sensor Devices

Calculate the heat index WBGT

What is the heat index WBGT?

WBGT; Wet Bulb Globe Temperature is one of the internationally standardized heat indexes.
The value is in degrees Celsius, making it an easy-to-understand index. However, a special measuring device called a wet bulb globe thermometer is required to measure it. There is also a simpler method of measuring it, which is created by the Japanese Society of Biometeorology (日本生気象学会), and estimated it from temperature and humidity. But, since there was no data below 20°C in the published table. So, I also used data from the other WBGT estimation formula derived from meteorological data for six cities by Masashi Ono of the National Institute for Environmental Studies (国立環境研究所).

Method of Calculation

The pseudo WBGT formula I created for indoor use is:

WBGT = 0.725*Ta + 0.0368*RH + 0.00364*Ta*RH – 3.246

Instruction

Schematic for Connection

Connect an I2C interface of M5Stack ENV II or III Unit to the GPIO header pins on your Raspberry Pi.

Fig. Schematic

The Simplest Code

Which is used the bc command. It’s useful for calculations on a Linux-based OS such as Raspberry Pi. You can get a WBGT value to substitute temperature for the variable TMPL and humidity for HUM, and execute the following command.

echo "0.725 * ${TMPL} + 0.0368 * ${HUMI} + 0.00364 * ${TMPL} * ${HUMI} - 3.246"|bc

Example:

pi@raspberrypi:~ $ TMPL=28
pi@raspberrypi:~ $ HUMI=90
pi@raspberrypi:~ $ echo "0.725 * ${TMPL} + 0.0368 * ${HUMI} + 0.00364 * ${TMPL} * ${HUMI} - 3.246"|bc
29.53880

Software on GitHub

URL of This Document

Authored by Wataru KUNINO