What You Need to Know About CO Sensors - Part 2 of 4

For part 2 of our series on what you should know about CO sensors, we will talk about portable CO monitors and one of the misleading characteristics of CO sensors—The false positive alarm.
 

Portable CO monitors

Portable CO monitors must rely on batteries to function, otherwise the “portable” aspect of them is moot. To make a device last as long as possible, it is necessary to use a sensor technology that doesn’t take a lot of power. That’s where EC sensors really shine! Because of their very simple design and operation, they require almost no power at all to operate. In fact, if it weren’t for all the electronics wrapped around the sensor itself so that you can interpret the output, one could operate on a single battery for decades! Just how low power are we talking about here? Let’s use a microwave oven as an example. A standard microwave uses about 1000 Watts of power. That’s a whole lot of juice! By contrast, the Sensorcon Protector uses just 90 Nanowatts (0.000000090 W) of power, which is 10 orders of magnitude lower than the microwave. That’s why the Protector can run for 5 years on a single battery.

This simplicity comes at a cost: Exposure to air is what kills them over time. The electrolyte inside the sensor has a finite life, and over time it dries out and loses sensitivity to the target gas. The average lifespan of an EC sensor is 2 years. This assumes that the sensor has seen ideal conditions throughout that lifespan. But there are many things that will decrease the life of an EC sensor, cause erratic readings, or even damage it beyond repair. These are the types of things most users are woefully unaware of, and so many headaches could be spared if they had been informed ahead of time. Let’s talk about some things that could cause those.

False Positive

A false positive is when the sensor shows a spike in readings when there isn’t actually gas present. This is a very common occurrence in portable sensors that are being moved between various environments. But what are the common causes of a false positive?

Problem: Thermal shock. This is when a device is quickly moved from a very hot or cold environment to the opposite. For example, a service tech from up north has their monitor sitting in their freezing cold truck during the winter. They walk the device into a nice warm house, and suddenly the reading spikes. Is it gas? Hard to tell without an actual known source of gas to verify against. How do you prevent a scenario like this?

Solution: Try to always allow time for your device to acclimate to a new environment if the temperature is vastly different from the one it just came from. Five minutes is usually enough unless the difference is like going from   -10° to +70° F.

Problem: Humidity shock. Just like thermal shock, a massive change in humidity can cause a spike in readings on the sensor for a short period of time. This is where product ratings are often ignored as well. Most sensors on the market will rate their humidity range from 10% to 90% non-condensing. Placing a sensor directly into a hot and humid air stream can cause erratic readings, and even cause the baseline to shift, which will make the readings look high for an extended period of time before settling down.

Solution: Just as with temperature, try to always allow time to acclimate to a new environment. Avoid placing your sensor directly into exhaust or process streams where high humidity and temperatures are present. Typically, if this type of analysis is needed, companies will offer special tools and sampling kits to safely deliver the air in the stream to the sensor without damaging it.

Stay tuned for part 3 of our series next week where we talk about other sensor behaviors that are often misinterpreted. Stay safe, and know your environment!