Indoor air quality monitoring products — why buying them may not be such a good idea

Indoor air quality monitoring products that do not specify their accuracy and reliability, expected product lifetime and how to use them properly should be treated as scams, according to a blog on halestrom.net.

Only a few designers realise that it is difficult to make WiFi-connected devices that provide more information than measuring temperature with an error of 5°C, humidity error of 50 per cent and pressure error of equivalent to 1 km in altitude, according to the writer of the blog.

An indoor air quality monitor is a gadget that gathers data on the particulate suspension, gases, and chemicals present in the air. The purpose is to identify trends and spot problem areas, and make adjustments accordingly.

Technicians, building owners and facility managers use indoor air quality monitoring systems to check airborne disease risk, identify areas that are not good for the occupant’s wellbeing, and detect anomalies such as mould growth.

According to the halestrom.net blog post, a device measuring temperature, humidity and pressure can be easily made by using an off-the-shelf sensor component and a PCB with a microcontroller or chipset that has wifi. While these individual sensor chips are cheap and can be found easily, they are seldom used correctly.

To ensure that the temperature measurement of a room’s air is a valid measurement, it needs to be kept far away from any other power-using electronics on the board. This is because even the smallest amount of heating from a main micro + WiFi chipset will impact the temperature of the nearby sensor. It is difficult to calibrate this error out as even a gentle breeze can vary it arbitrarily.

A change in temperature will also modify the relative humidity which is represented as a percentage of the maximum water capacity of air at its current temperature. As a few degrees change in the temperature will change how much water can be stored in the air, the percentage of humidity will read incorrectly, the blog said.

In order to use a temperature, pressure, and humidity chip correctly, one needs to put it far away from the rest of the chips on the board, ensure that the product is labelled with an arrow showing which way to mount it, and not have any copper fill near the chip.