Analog signal and DC Drive issue

NBJamie99

Lifetime Supporting Member
Join Date
Jun 2008
Location
Ohio
Posts
32
Hello all and thanks in advance for the help.

I have been asked to use an existing drive with a new control system. At the moment I have it fully setup other than the speed reference.

Old setup:
This drive internally produces a 0 to -10 volt signal which was then ran to a 500Ohm Pot(-10 to top, a special +.2V to bottom, and a shield connected to common, and the reference signal), and the returned signal was the speed reference, 0 being 0% and -10V being 100%.

Verification:
I have looped the -10V directly into the input for the reference signal on the drive and everything powered up and moved correctly.

Attempt 1:
I have a MicroLogix PLC with a 1769-OF2 Analog output module, which is configured to output -10 to 10, and scaled in the ladder to output 0 to -10 just as the drive was setup to receive. I connected the common from the output card to the common of the drive, and the output V+ from the card to the speed reference input on the drive. This did not work.

Thoughts:
Find a device that will accept the 0 to -10 from the drive and adjust an output signal from that source, based on an input from my PLC. I am not sure what sort of signal conditioning or isolation terminology such a device may be called, does anyone have some thoughts? Please list links to possible device information, if possible.

Thanks,

Jamie
 
I ran into a simliar problem years ago. The issue is with the drive. The analog signal is not isolated from the drive. Basically what you need is an isolator to correct the issue. You sould be able to contact the maker of the DC drive and they will be able to sell you one.
 
I have been jumping from sites and catalogs to track down an Isolation module that will work, but guess I am having issues determining the function. I have been looking at the Phoenix MCR-C-UI-UI-DCI and the description of the function sounds like what I would like, but I can not tell from the print of the function how that is possible.

That module is a 3-way isolation device, where Input/Output/Power are all isolated from each other. The print does show a separate ground for each section of the module, but I am not clear on where the signal voltage is coming from; or since it is isolated and grounded to the drive, would that not be an issue? I would just hate to buy one of these modules and have it not work.

Thanks
 
try this one:
Transducer, 3 way isolated, Siemens, 3RS17 06-1FE00

i have used it several times...
they use an internal transformer to isolate and create a supply for the output
 
That had a very good explanation with it, and is exactly what I could use, but it does not function for negative voltages. But thanks for the lead.
 
What is the DC drive manufactor. They probably have an isolator for that drive. Most mount directly to the drive itself.
 
The drive is a Saber 3306, the manual can be found on yaskawa's website, but they no longer support the drive. That has been passed on to anther company.

I called the service line, and he agree that it did not work because it is not isolated. He also said they have not done anything with these drives in a long time, but remember them using an action something, which I thought was probably an action pak from action instruments. He also said he thought phoenix contact makes something similar.

I also called AB and asked about their Isolated output cards, and he informed me it is not the type of isolation that I am looking for. He proceeded to tell me that if I used an isolator, to make it work I could connected they output of the isolator and the -10 output from the drive to the reference terminal. So that if I am outputting +10V and they drive has the -10 it will sum to 0, and as I reduce the +10 the sum will go negative, which will increase the speed of the drive.

I was thinking about testing a Phoenix MCR-C-U-U-DC, I figure I could start by powering if from the 24V created on the drive, connect my signal from my analog card and connect the output to the speed reference.

If that does not work I would try what the AB guy suggested with the opposing voltage sources.

Any thoughts?
 
attempt1:
why don't you try with the plc analog output module and put a resistor on the output (check the load acceptable for the module).

attempt2:
connect the output of the isolator to the common of the drive, and the common of the isolator to the speed reference input on the drive. in this way the signal will be reversed.
 
I have used the Action Pak brand isolators before in a similar situation.

You may have to reverse the polarity of the isolator output, and get one with separate zero and span adjustments so that you can best simulate the desired signal

Even then, it still may not work, depending on the input impedence of the drive.

I don't recall the particular model number of the ones we used, but it was very user friendly, versatile and reliable.

If worse comes to worst, and the isolator won't help, you can always use a motor operated pot...do they still make those?

Paul
 

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