Downloads

Here you'll find the latest firmware, user manuals and changelogs for all MoreSense sensors. Firmware updates can be installed easily "over the air" via the built-in web server of your sensor – see the user manual for instructions. Questions? Feel free to contact us.

MS-07

VOC Index and NOx Index explained

The MS-07 shows VOC and NOx as an index, not in ppm or µg/m³. That can be confusing at first, so here is what the numbers mean. Both indices come from Sensirion's gas sensor technology (also used in the SEN66 inside the MS-07) and its Gas Index Algorithm.

Why an index instead of a concentration?

Indoor air contains hundreds of different volatile compounds, and their mix changes constantly. A small, affordable gas sensor can't reliably tell them apart or measure each one exactly. What it can do very well is notice when the air changes compared with what is normal for your room – a bit like your nose, which picks up a new smell when you walk into a room but gets used to it after a while. The sensor learns that "normal" from a moving average of the previous 24 hours.

VOC Index: 1 to 500, normal is 100

The VOC Index runs from 1 to 500, and the usual background level of your room is always shown as 100.

Below 100 – cleaner than usual, for example after airing the room or running an air purifier.
Around 100 – normal for this room.
Above 100 – more VOCs than usual: cooking, cleaning products, perfume, paint, candles, or simply a lot of people in a room. Values above about 150–200 are a good reason to ventilate.

NOx Index: 1 to 500, normal is 1

The NOx Index reacts to nitrogen oxides and other oxidizing gases. Most of the time there is hardly any NOx indoors, so the normal level is 1.

Around 1 – normal, no NOx events.
Above 1 – something is producing NOx. The most common indoor source is cooking on a gas stove; traffic fumes coming in from outside also count. Opening a window or running an air purifier brings the index back towards 1. A value above about 20 is a sensible trigger to start ventilating.

Good to know

After switching on, the sensor needs time to learn your room; the readings become meaningful after a few hours and fully settled after about a day.
Because the index is relative, two rooms showing the same value don't necessarily contain exactly the same amount of gas – the number tells you how much the air differs from what is normal there.
Looking at VOC and NOx together tells you more: cooking on gas raises both, while cleaning products or perfume mainly raise VOC.

Want to know more? Sensirion explains the technology in two short information notes:

MS-06

MS-05

User manual available in English and Dutch.

MS-04 LED matrix display

User manual in Dutch.

MS-02

Please note: from firmware version 1.7.1 the e-mail option has been removed. User manual in Dutch.