Sensor to Measure Oil Residue in Compressed Air

Yes, I know this solution, but this is as I wrote, complete device, I'm interested only in sensor (OEM solution).

Anyway, thanks for trying.

That is exactly what I want to do :)

Wow! that's a million dollar question. I wish I knew the answer.

The purpose of final use will point to where you start. Consider:

Is it in-house or a product for sale. The source of compressed air.

You must define exactly what you mean by 'oil residue' because you then mention 'oil vapour' - your research will reveal there is a vast difference. Detecting and measuring techniques are different for each.

The cost of capital and maintenance of the monitoring system.

The standards you propose to use for testing and calibration, and hence the audit trail for quality control (for others) to independently substantiate the claims you make.

ISO 8573 and a whole host of associated parts should help (or hinder).

This is for starters.

I want to use it to monitor oil content in air stream after the dryers and filters, air should comply to ISO 8573 class 2, most likely the oil should be present only as vapour.

Dew point of this air stream will be in between -20 to -50 degrees Celsius.

Final application is to monitor compliance of air stream according to ISO 7396-1:2010 standard.

And ofcourse it hast to be achieved the cheapest way possible :)

don't know about ISO 7396:2010. There is a 2007 version up-dated with amendment A3. Is that the one you mean.

"... most likely the oil should be present only as vapour..."

In which case you will need a sensor able to detect oil vapour with results traceable/correlated to comply with ISO 8573:Part 5: Test methods for oil vapour and organic solvent content., but if comprising less that 6 carbon atoms then you need to comply with Part 6: Test methods for gaseous contaminant content.

In all probability oil vapour itself will not be an issue, it is the oil aerosol (when things go wrong?) so you need a sensor able to detect oil droplets with results traceable/correlated to comply with ISO 8573:Part 2: Test methods for aerosol oil content.

The completely different approaches to detecting and measuring 'oil' in compressed air are outlined in detail in these 3 parts of ISO 8573 - so you will probably guess that had a sensor existed that would do all 3, it would be in regular use. And if successful would remove the need for these standards.

I think you need some luck if you hope to find one, especially a cheap one.

I wish you well.

@horace40

OK. I've done some digging, and it seems that in my case the "Oil may be present as liquid, aerosol and vapour." this is quote from standard ISO 7396-1.

Also my air stream must comply with class 2 (oil content not higher than 0,1 mg/m3).

I'm not very familiar with the standard 8573.

Does it mean that in my case I will need 3 different types of sensors? I think that I will have no other option but to buy these standards.

As cheap I meant, that my goal is to make a device that would be cheaper than the ones existing on the market. As you know cheap is a relative matter. Simply I don't want to pay 6000 EUR, for something that maybe I can build on my own with the use of proper sensor.

Anyway thank you all very much for your help.

Here is a list of the 9 parts:

ISO 8573 consists of the following parts, under the general title Compressed air :

- Part 1: Contaminants and purity classes

- Part 2: Test methods for aerosol oil content

- Part 3: Test methods for measurement of humidity

- Part 4: Test methods for solid particle content

- Part 5: Determination of oil vapour and organic solvent content

- Part 6: Determination of content of gaseous contaminants

The following parts are in preparation:

- Part 7: Test methods for viable microbiological contaminant content

- Part 8: Contaminants and purity classes (by mass concentration of solid particles)

- Part 9: Test methods for liquid water content.

Part 1 gives the quality classes, and the other 8 specify the test method to see if (the chosen class of) pt1 is being met.

Linked to the 8573 series is ISO 12500 series. These spell out the tests filter/dryer people must carry out on their products to demonstrate claims of compliance with 8573.

I doubt if buying a set of each of these will help much.

More to the point is that if any class of ISO 8573 is called on by ISO 9678, the supplier and installer will need to demonstrate compliance at commissioning. Not your problem.

Testing the air at a later date (I guess this is the purpose of your product) is to show continued compliance - which is a maintenance problem.

Building a quantitative device is a lot more complex than a relatively simple device to look at failure mode, where a qualitative result might suffice.

The natural state of compressed air is hot, wet and oily. Neglect maintenance, and that is what you get.

Building a device to detect failure early on (not just oil) could be a better proposition.

In my country we have only first 3 parts.

Part 2 and 3 are rendered absolute. The rest is not available.

This what you say is my problem, cause I must prove that some certain objectives were achieved at the commissioning.for now I'm achieving this with Dreager Multitest but I want to build something that is multi use.

Maintenance is not always a problem, sometimes it is the quality of filter elements, or dryers itself. I'm dealing with medical market for couple of years now, and this what I want to achieve is to put a new quality on the market, a complex solution to monitor content of all components of air that we breath in, in compliance to medical standards.

The only thing that I broke my teeth on is the oil content. Thats where my question is coming from.

What is your country? Just curious.

My expertise is in compressed air for breathing for industrial air supplied respirators. Very similar to medical air but Europe works to EN12021. We use the BS EN version in the UK. I have been retired for 13 years so I am out of touch of what is happening on industrial sites today.

But during my time I searched for instruments to measure contaminants, but like you, with no real success where oil was concerned. Usual practice in those days, for on-site instant results, was to use colour change detector tubes. The alternative was to collect samples that were sent away to laboratories for analysis.

These methods are still used today as far as I know, except in recent years Factair have used a Draeger impactor test for oil aerosols in their portable Air-Test kit

That still leaves oil vapour, which can be tested using Draeger tubes.