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Air compressor shows wrong pressure with replacement pressure probe

pMetal

Aluminum
Joined
Jul 14, 2014
Location
United States
I'm bringing our old air compressor back to life after being in storage for several years.

It is a 25hp Chicago Pneumatic (Atlas Copco) brand rotary screw machine (Model QRS25). The controller on it is a model ES3000. At some point in the past we damaged the pressure sensor (also known as pressure transducer or pressure transmitter) while doing maintenance.

Chicago Pneumatic support doesn't answer the phone or emails, so I ordered a generic pressure transducer from McMaster (one that reads up to 200psi, for 12V, which outputs 4-20mA).

It works, but the compressor's pressure reading is way off: When depressurized, the control displays 28 psi (when actual gauge pressure is 0 psi). And when the compressor is running, the control displays 116 psi (the setpoint), when the actual gauge pressure is only 75psi.

So I bought another pressure transducer... This time from a company that makes aftermarket parts for Chicago Pneumatic machines, which was cross-referenced with the OEM part number. This gave the same exact results.

I don't see a parameter in the control that allows me to calibrate pressure transducer reading, and I certainly don't see a way to calibrate for non-linear results (since the pressure error is greater at higher pressures than at lower pressures).

The controller manual says that the proper transducer goes to 17 bar (which I believe is 247 psi), so maybe the fact that I first bought a 200psi transducer explains the error in the readout. However, since the second time I bought a transducer, it was supposedly an OEM replacement, now I am wondering if there is some other issue.

Do you think the issue is simply that I need a 247psi (or 250psi) transducer to get the correct readings? Or do you think there is some other problem (such as a bad controller board)?
 
The difference 116 - 28 = 88 psi. The gauge reading is 75 psi. Gauges are not accurate.
The thing is working. The zero is not adjusted. Does the controller board have any small potentiometers?
 
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Rons is headed in a productive direction... Adjusting the hysteresis (2 pots?) to get the control to turn on and shut off at the correct gauge pressure is the goal.

Does the aftermarket company have tech help?
 
Yes, I didn't want to get into detail. But, is there a "zero" pot and a "Span" pot?

I use these little SMC pressure switches. I like them so much that I have two spares.
I use one on a compressor. The set points are adjustable by the push buttons.
They also make analog output models. Don't know, but it appears you could use
one to satisfy you current loop. But all you really need is just a simple on-off switch.


I use this on my compressor:

I have a couple Festo switches for spares too:


The only thing is the output is a small transistor. So you can't pull in a relay or contactor coil all by itself.
I'm using it with VFD that takes digital inputs.

Have you ever bought a pair of running shoes and liked them so much that you had to back and buy two more pairs?
 
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The difference 116 - 28 = 88 psi. The gauge reading is 75 psi. Gauges are not accurate.
The thing is working. The zero is not adjusted. Does the controller board have any small potentiometers?
I think you're right.

There's no potentiometers, but there are various parameters on the control (its all digital). The manual shows a parameter for "offset on pressure reading", however with a note that it is only on later versions of the control. And, as it turns out I'm out of luck and that parameter is not available on my controller.

So, for now I've adjusted the control to tell it to output 200 psi (the max that the control will allow), and it is actually (per gauge) at around 120psi.
So it is usable for regular shop use now.

However, my plan was to use this compressor a particular application that requires higher pressure than that, so I'm going to buy yet another pressure transducer (this time one for 250 psi) to see if that gets the display to the correct pressure.
 
You could test this yourself with a current meter. Maybe even a DIY current source to see what the board was matched with.
I looked up your model and wow, 23K dollars at Grainger.

I rate Omega very high:
 
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I think you're right.

There's no potentiometers, but there are various parameters on the control (its all digital). The manual shows a parameter for "offset on pressure reading", however with a note that it is only on later versions of the control. And, as it turns out I'm out of luck and that parameter is not available on my controller.

So, for now I've adjusted the control to tell it to output 200 psi (the max that the control will allow), and it is actually (per gauge) at around 120psi.
So it is usable for regular shop use now.

However, my plan was to use this compressor a particular application that requires higher pressure than that, so I'm going to buy yet another pressure transducer (this time one for 250 psi) to see if that gets the display to the correct pressure.
Crazy question. Motor and other internals rated for 200 PSI? Bad things could happen if not.
Our 20hp Atlas screw kept freezing internally and popping the safety valve, fogged the shop if not caught. So one of my guys replaced it with a pipe plug. Problem gone. Forgot to shut it down and it stayed on all weekend. Monday morning that same guy went over it because it started making a loud sound. Got there just in time for the oil filter to explode. Blew off some of the sheet metal and major oil mess.
 
Crazy question. Motor and other internals rated for 200 PSI? Bad things could happen if not.
Our 20hp Atlas screw kept freezing internally and popping the safety valve, fogged the shop if not caught. So one of my guys replaced it with a pipe plug. Problem gone. Forgot to shut it down and it stayed on all weekend. Monday morning that same guy went over it because it started making a loud sound. Got there just in time for the oil filter to explode. Blew off some of the sheet metal and major oil mess.
That's what these jewels are for. I use one on a 120 gallon tank and one on the compressor pump, intake side of second stage.

 
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I feel your pain. I have a similar issue with Kaeser. They refuse to provide help in acquiring manuals and technical support. They have repeatedly referred me local dealers for support. They would not even deliver a part number of the air/oil separator filter. Yet, when I call and or send emails to these dealers, I never get a response. Some member hear stated that these compressor companies consider advice and technical support are profit centers, but that does not answer the reason for no answers.
 








 
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