humidity inside pneumatic air lines

piscis said:

Has anyone here has had good experience and can recommend an analog sensor capable of measuring the humidity inside pneumatic air lines?

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Is condensation an issue with your compressed air, or are you looking for a way just to measure?

If condensation is an issue, then your compressor will need a dryer to remove condensation and all panels such have a filter regulator combination to remove moisture

The big question is how dry do you really need the air? If you are running drill motors and other air motors you can have moisture
valves and actuators less
really small valves with very small orifices and high precision much less water.

Drying air can be done to almost any level you need but the dryer you go the more money it takes to do it.

Since you are near equator you really need to dry your air. You have 3 methods - install them between compressor and receiver
1. Put in compressed air to water or ambient air heat exchanger. If you use a water one you can provide all your hot water needs. Estimates are you can recover 50 % of complressor motor power.
2. Desicant dryers. These take electricity to dry the desicant but work well
3. Refrigerated air dryers work very well but again take electricity

Piping should be installed to leave the water in the header. Branches to point of use should come out the top of the pipe. Drains out the bottom. Ingersoll Rand and other compressor makers have good info on how to install these systems.

You also want to put in particulate filters before each application to catch pipe scale and you want to put in oilers to lubricate equipment.
Vasaila has many sensors for measuring water content in air. It is not that simple as just relative humidity since that is affected by both actual water content (%/% or weight / weight) and by ambient temperature. I would check with them or a compressor maker ie Ingersoll Rand.

Dan Bentler

That's an interesting one I to would like to find a sensor for this type of application, we have driers but on two occassions we had a problem with them without anybody nowing, as we have hundreds of APV ASI valves (these contain very small solenoids) we had many that failed, normally a good clean & lube will do the trick but these are fiddly & don't work very well after dismantling, I would like to monitor the amount of condensation to pre-warn us so if I find a sensor that is suitable I will post the results.

This is a good one and I'm going to watch this post.
I have customers with well designed and maintained air systems and the dryer stopped working. There is no alarm on that part of the system so the air system filled with water before anyone knew there was a problem.
Perhaps if we had a way to monitor incoming air for excessive moisture we could prevent a lot of problems.

Parky

If you have really moisture sensitive valves you can put a small moisture separator up stream - can double as particulate. Then place oiler. Too much oil can slow em down but that is almost always self curing unlike water or particulate.

Also put drain valves in your distribution headers. If automatic then weekly go around and open the manual you put in parallel to ensure the auto is working.

Dan Bentler

parky said:

That's an interesting one I to would like to find a sensor for this type of application,

Click to expand...

gas said:

This is a good one and I'm going to watch this post.
I have customers with well designed and maintained air systems and the dryer stopped working. There is no alarm on that part of the system so the air system filled with water before anyone knew there was a problem.

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Parky, Gas,

I have no idea if this will work (I have not tried it). Previously I had heard of an aspirin pinched under the lever of a microswitch. Supposedly the aspirin will crumble when wet allowing the microswitch lever to move and complete a circuit.

There is also this thread that has some links to some products, albeit not designed for compressed air.

http://www.plctalk.net/qanda/showthread.php?t=26970&highlight=detect+water+floor

piscis said:

Has anyone here has had good experience and can recommend an analog sensor capable of measuring the humidity inside pneumatic air lines?

Click to expand...

Try http://www.vaisala.com. Very good at measuring humidity or dewpoint.

Danny,
That stuff is for meteorological use but you just gave me a good idea. I know that the HVAC guys measure humidity of moving air in ductwork. One of those guys is pretty sharp and I'm going to pay him a visit in the morning.
Thanks

Vaisala appears to have the answer. Dew point sensor for compressed air
see
http://www.vaisala.com/instruments/applications/plastics-compressedair.html

This one looked good to me
Vaisala DRYCAP® Dewpoint Transmitter DMT242 - spec sheet at
http://www.vaisala.com/instruments/products/dm-dmt242.html

Dan Bentler

Yep, our Oriad dryer system (from Kemp) uses a dewpoint sensor to switch dryers and to alarm at a high dewpoint.

I am very interested in seeing if it is possible to sense the humidity in an air line.

A quick Google came up with this. I don't like their package but I wonder if you could purchase the sensor from them
http://www.airbearings.com/humidityalarm

TWControls said:

I am very interested in seeing if it is possible to sense the humidity in an air line.

A quick Google came up with this. I don't like their package but I wonder if you could purchase the sensor from them
http://www.airbearings.com/humidityalarm

Click to expand...

If you are doing air bearings for sure you do not want water near them.

Water can condense in the headers especially so if run outdoors and subject to freezing. With air bearings I would have a receiver to act as a water trap and a drain valve to give me an idea of how much water I am NOT removing back at dryer and then a sensor to measure water content of air. I posted a couple links to Vasaila above.

Dan Bentler

I contacted Vaisala and settle for their 4-20ma Analog Sensor:

Dewpoint Transmitters for Compressed Air Monitoring
Model number #DMT 242 S2D1AOB
They were quoted at $1,147.50 each.

I’m not sure if these sensors are isolated so I need to find out about this. I will bring the signal to my PLC and build a monitoring and data collector HMI package. Thank you all so much for your great replies.

I’m just curious if anyone here will be able to comment between these two technologies for reliably sensing dewpoint?

Thin film polymer sensor
Vs’
Chilled Mirror sensors