- Question Title: Variable speed drive air compressor
- Asked by: Guest
- Asked On:
- Answers: 1
The Yaskawa F7 VFD Installed on Our ALUP SCD 80 is not reading the 4-20mA signal ( for the analog speed reference command) from the Air Control 3 Module.
The Yaskawa dealer Tech says the Air Control 3 is putting out a 4-20 mA signal that is too weak to read.
The Alup Tech says the 4-20 Ma Signal is fine, and he can measure it, and it is operating properly.
The end result is that we have a compressor that will not run and no one knows how to fix it. It has worked fine since 2005, and now this.
How do find a technician that can work on both a Variable speed drive and a compressor control at the same time ?
Answers & Replies
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Hello Ryan,
Thanks for your question. I understand your frustration, as I have encountered such situations numerous times: the people that are supposed to fix the problem all point to each other :) I have seen it a lot, not only with compressors, but with many different machines..
Well, what can I say? "putting out a 4-20 mA signal that is too weak to read. " sounds a little strange to me. 4-20mA is 4-20mA. It is not a voltage signal, it is a current, so it can not be 'too weak'. If the Alup was designed to output 4-20 mA, and the Yaskawa was designed to read 4-20mA, than it should just simply work.
More info about 4-20mA loops can be found here:
Understanding current loops
and troubleshooting current loops
I'd love to come over to Seattle to help you, but I guess that's not possible :)
My advice would be to first check the output of the compressor controller. Does it really output 4-20mA? I understand the tech did that and it was OK.
Next, get or borrow a 4-20 mA tester. This is a small device that can simulate 4-20mA signals. Connect it to the Yaskawa. Is it reading that signal properly?
If not, there is something wrong with the Yaskawa.
If it does read the 4-20mA signal from the simulator properly , then the compressor controller and the variable speed drive are incompatible for some reason...
In that case, I would suggest to install a 4-20mA signal conditioner/converter/buffer in between. Set it up in such a way that it accepts an input of 4-20mA and has an output of 4-20mA, so noting really changes signal-wise (it just acts like a buffer).
These device can be found here or here for example (just two examples, all mayor electrical brands have these things.. search for: 4-20mA buffer, 4-20mA isolator or 4-20mA converter).
Hope this was helpful and good luck finding a good technician :) If you need any more help, just let me know!