tmassey
Contributor
Here is a quick write-up of my carbon monoxide (CO) calibration / bump-gas setup. I had previously written up my experience as a comment in a different thread (see below for details) but it's poorly named and spread across multiple posts, so I thought I would combine it all in a single easier-to-find post.
In order to do this, you need a source of calibration gas, a "regulator" (or valve) to dispense that gas from the bottle, and some hose to plumb the gas from the valve to the sensor.
The trickiest part is getting the calibration gas. Shipping pressurized cylinders is always hard, because they need to be shipped as hazardous material. That means that the only real source of affordable calibration gas is a local supplier. And the only easily-found local source I've been able to find is Grainger. By picking it up at your local Grainger location, you avoid having to pay for hazardous material shipping.
Unfortunately, Grainger only sells to businesses: you will need a business tax ID. I have such an ID, so it was straightforward for me. If you don't, ask businesses that have any kind of maintenance department if they have a Grainger account: it's highly likely that they do, and they might be willing to throw your cylinder on their next order. And given the difference in price, it's worth the effort to make this happen.
From what I've seen, most CO analyzers are designed to use 50 PPM as the gas for calibration. Here's the Grainger link for that gas: Grainger GASCO Calibration Gas. In case the Grainger link goes away, it's Grainger Item 23YK59, GASCO Item 17L-50-50.
When bought it in 2020, it was under $30. Now it's double that. The last five years have been a wild economic ride...
Once you have your calibration gas, you need a way to get it out of the bottle. The small calibration gas cylinders that are likely to be used by us amateurs are similar to small disposable propane cylinders and use a similar connection: CGA-600. And you can use the same types of valves/regulators you would use for such cylinders. This might include repurposing an old O2 regulator, or could be as simple as a modified torch.
I didn't really have any such items laying around, so I purchased one new. I ended up going with a very simple valve sometimes marketed as a "regulator": the Gasco Calibration Gas Control Valve CV-2.
gasco-gas.com
I purchased mine on Amazon, but Amazon links don't seem to last much longer than eBay links, so here's a photo so you can see what I'm talking about and find your own current link:
As you can see, it's simply a CGA-600 connector, a needle valve and a barbed fitting. About as simple as it gets.
If you want to get fancy with it (and I almost *always* want to get fancy with it...), you can add in an inexpensive acrylic flow meter. I used a 1000mL (1L) flow meter I picked up on eBay for less than $10 shipped (back before the end of the world in 2020). I like having flow meters in such applications: it's always nice to be able to take a look and see that yes, Virginia, gas is indeed flowing, yet not so much as to be wasting my rather expensive calibration gas. One of my sensors specifies a specific flow frate, so this allows me to meet that. But again: we're not really worried *that* much about high-precision, so just make sure there's a perceptible flow and you should be fine.
Speaking of: I purchased the 17L cylinder of gas, and I'm still using it 5 years later. I calibrate twice a year and I have two sensors. Of course, right now the 34L cylinder is only about 15% more expensive, so maybe you choose to buy that one instead; but know that even the small cylinder will last you just fine for quite a while.
From there, you just need the proper tubing to go from the valve to your sensor. If your sensor came with a calibration cover, you might need to adapt your hose down to fit it directly. Otherwise, just aim the end of the hose directly at the sensor. In our case, we're not really trying to carefully measure the exact CO concentration: we just need something that lights up when CO of any kind is detected. So simply pumping CO directly at the sensor should be fine. I ended up with mostly 1/8" ID vinyl tubing, with a few pieces of 1/4" ID tubing to mate with the barbs on the flow meter. I simply used wire ties to hold everything together: there isn't enough pressure or flow involved to justify more than that -- and you're only going to be running it for a handful of seconds anyway.
One other thing: if your sensor supports recalibrating the zero point and the CO point, do both: I'm pretty sure only doing the CO point calibration led me to some false positives.
Anyway, this is a very simple setup. Calibration gas cylinder from Grainger, CGA-600 valve from Amazon, flow meter from eBay and vinyl tubing and wire ties from Home Depot to tie it all together. 60 seconds or so of gas flow twice a year and I have properly calibrated CO sensors. Well worth the $60 I spent in 2020, and probably still worth the $120 or so you're likely to spend in 2025. Hope this helps others to find this information more effectively in the future!
Link to original posts: Source For Replacement Sensors in the US and Elsewhere
Link to review of an inexpensive Carbon Monoxide sensor I've been using for a while now: Forensic Detectors Carbon Monoxide (CO) Detector Review
In order to do this, you need a source of calibration gas, a "regulator" (or valve) to dispense that gas from the bottle, and some hose to plumb the gas from the valve to the sensor.
The trickiest part is getting the calibration gas. Shipping pressurized cylinders is always hard, because they need to be shipped as hazardous material. That means that the only real source of affordable calibration gas is a local supplier. And the only easily-found local source I've been able to find is Grainger. By picking it up at your local Grainger location, you avoid having to pay for hazardous material shipping.
Unfortunately, Grainger only sells to businesses: you will need a business tax ID. I have such an ID, so it was straightforward for me. If you don't, ask businesses that have any kind of maintenance department if they have a Grainger account: it's highly likely that they do, and they might be willing to throw your cylinder on their next order. And given the difference in price, it's worth the effort to make this happen.
From what I've seen, most CO analyzers are designed to use 50 PPM as the gas for calibration. Here's the Grainger link for that gas: Grainger GASCO Calibration Gas. In case the Grainger link goes away, it's Grainger Item 23YK59, GASCO Item 17L-50-50.
When bought it in 2020, it was under $30. Now it's double that. The last five years have been a wild economic ride...
Once you have your calibration gas, you need a way to get it out of the bottle. The small calibration gas cylinders that are likely to be used by us amateurs are similar to small disposable propane cylinders and use a similar connection: CGA-600. And you can use the same types of valves/regulators you would use for such cylinders. This might include repurposing an old O2 regulator, or could be as simple as a modified torch.
I didn't really have any such items laying around, so I purchased one new. I ended up going with a very simple valve sometimes marketed as a "regulator": the Gasco Calibration Gas Control Valve CV-2.
CV-2
This valve/flow meter offers a low cost and convenient method of gas flow regulation. Specifications Part #: CV-2Valve Inlet: CGA 600Outlet: NAFlow Rate: VariableGauge PSI: NAMa…
gasco-gas.com
I purchased mine on Amazon, but Amazon links don't seem to last much longer than eBay links, so here's a photo so you can see what I'm talking about and find your own current link:
As you can see, it's simply a CGA-600 connector, a needle valve and a barbed fitting. About as simple as it gets.
If you want to get fancy with it (and I almost *always* want to get fancy with it...), you can add in an inexpensive acrylic flow meter. I used a 1000mL (1L) flow meter I picked up on eBay for less than $10 shipped (back before the end of the world in 2020). I like having flow meters in such applications: it's always nice to be able to take a look and see that yes, Virginia, gas is indeed flowing, yet not so much as to be wasting my rather expensive calibration gas. One of my sensors specifies a specific flow frate, so this allows me to meet that. But again: we're not really worried *that* much about high-precision, so just make sure there's a perceptible flow and you should be fine.
Speaking of: I purchased the 17L cylinder of gas, and I'm still using it 5 years later. I calibrate twice a year and I have two sensors. Of course, right now the 34L cylinder is only about 15% more expensive, so maybe you choose to buy that one instead; but know that even the small cylinder will last you just fine for quite a while.
From there, you just need the proper tubing to go from the valve to your sensor. If your sensor came with a calibration cover, you might need to adapt your hose down to fit it directly. Otherwise, just aim the end of the hose directly at the sensor. In our case, we're not really trying to carefully measure the exact CO concentration: we just need something that lights up when CO of any kind is detected. So simply pumping CO directly at the sensor should be fine. I ended up with mostly 1/8" ID vinyl tubing, with a few pieces of 1/4" ID tubing to mate with the barbs on the flow meter. I simply used wire ties to hold everything together: there isn't enough pressure or flow involved to justify more than that -- and you're only going to be running it for a handful of seconds anyway.
One other thing: if your sensor supports recalibrating the zero point and the CO point, do both: I'm pretty sure only doing the CO point calibration led me to some false positives.
Anyway, this is a very simple setup. Calibration gas cylinder from Grainger, CGA-600 valve from Amazon, flow meter from eBay and vinyl tubing and wire ties from Home Depot to tie it all together. 60 seconds or so of gas flow twice a year and I have properly calibrated CO sensors. Well worth the $60 I spent in 2020, and probably still worth the $120 or so you're likely to spend in 2025. Hope this helps others to find this information more effectively in the future!
Link to original posts: Source For Replacement Sensors in the US and Elsewhere
Link to review of an inexpensive Carbon Monoxide sensor I've been using for a while now: Forensic Detectors Carbon Monoxide (CO) Detector Review
