What You Need to Know About CO Sensors

How long does it take for a home carbon monoxide detector to go off? People tend to believe that the answer to that is “As soon as the level of carbon monoxide passes the limit, of course!”, and while that does make logical sense, that actually isn’t the way home carbon monoxide detectors work. Most people don’t know how carbon monoxide detectors work — and that’s okay because it’s a specialized topic. How often do you talk about detecting carbon monoxide in regular conversation? Probably not very often!

I have spent nearly 20 years of my life designing gas detection devices. In that time one thing has been made abundantly clear: Unless people are specifically trained on how gas sensors operate, they will often misinterpret readings, think their sensors aren’t working when they actually are, or expose them to harsh environments or chemicals that adversely affect the sensor. There are numerous ways gas sensors can be affected by the surrounding environment that could lead to false readings, low sensor output, sensor instability, or dead sensors.

In an ideal world, a carbon monoxide sensor would last forever and stay accurate for its whole life. Unfortunately, no such technology exists. The vast majority of carbon monoxide sensors on the market today utilize either “electrochemical” (EC) sensors, or metal oxide sensors (MOS). Each of them has their own pros and cons, as well as use cases that are best suited for them. Beyond the sensor technology types, there are also large differences between how sensors are expected to respond with various product types, which the average consumer is typically unaware of. Let’s talk about the various types of products and how users expect them to work, how they actually work, and what can typically go wrong on them that most people may not even be aware of.

These are the kind that you typically plug into a wall at home to keep you and your family safe from carbon monoxide buildup. The kind that plug into a wall usually use a metal oxide sensor. These types of sensors consume far too much power for a battery operated device but are very well suited to line power where they will add nary a few cents on your electric bill.  These types of sensors are very cost effective, and in a predictable environment like a home, can last for a very long time without having any issues. I mention a predictable environment because one of the main caveats of metal oxide sensors is their cross-sensitivity to other gases and their ability to become “poisoned”. In a home environment, at most these sensors may be exposed to noxious fumes from cleaning chemicals periodically, but rarely directly or for long periods of time. Out in the world where things are more chaotic, direct exposure to gases like hydrogen or various VOCs can degrade the sensor performance substantially, even killing the output entirely. This is why electrochemical sensors are the go-to for applications away from the home. There are some electrochemical CO detectors for home use, they typically look just like the plug-in kind but operate for 5-10 years on a battery.

Home CO detectors are all built to a particular standard called the UL 2034 standard, which the US government has adopted as the general law for how they’re supposed to function. People that are familiar with the function of wearable CO monitors with a display might be surprised to know that the alarm limits for home detectors are significantly higher than the safety limits set for worker exposure by OSHA.

The limits set by the 2034 standard are shown below.

These limits are set higher to try and account for false positive readings, as the average consumer cannot be expected to be fully trained on how these technologies work, and it would be a great inconvenience and strain on emergency services to be constantly responding to calls when it could just be a sensor acting strangely. However, more and more data on the adverse effects of long-term exposure to low levels of carbon monoxide are coming to light, and the informed consumer might find themselves wondering how they can be better protected or informed of their environment at home. That is where devices like the Sensorcon Inspector and Protector series come in. With real-time gas concentrations being shown on the display, user-configurable alarm points preset to OSHA standards, and industry-leading battery life, users can always feel safe and informed about their environment. Sensorcon’s devices, like most portables on the market, utilize electrochemical sensors. Stay tuned for part 2 next week, where we will discuss portable CO monitors and the issue of false positive alerts!

Dave Massner
Sales Engineer - Sensorcon
dave.massner@molex.com
p. 316-828-0015