Llama118

VFD Analog output to LOGO!

17 posts in this topic

Hullo neighbors, 

We've got a LOGO! 0BA8 configured to use I8 as an analog input,
and the goal is to read the current operating speed of an ABB ACS310 VFD.
(we want our PLC to be able to react to any changes in speed from the VFD)

Problem is, nobody can figure out how to hook up the analog output from the VFD to the analog input on the PLC.

Have tried going from AO -> I8 and have also tried adding a connection from the LOGO! input neutral back to the GND... nothing works. 
Attached is the terminal diagram for both devices with our poor attempts labeled.
Any insights?
 

VFD to PLC attempts.png

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Seems to be ok the wiring.

Did you set the I8 as analog input?

How it looks the LOGO program?

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I7 and I8 are configured as analog inputs. We have a test program in LOGO displaying the voltage coming in from each connection.

They'll read a digital input correctly as 10v. All we're getting from this connection to the VFD is apparent phantom voltage floating around 1v. It's fluctuating, and it doesn't change regardless of the speed of the motor or the settings on the VFD.

 

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Have you verified the configuration of the analog output in the drive? I'm not familiar with ABB hardware, but it could be that the analog output is disabled in a parameter or is configured to represent something else.

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Yes, and we've tried several other configurations to see if we get anything different, but nothing seems to change the output from that floating volt.

I was convinced we must be missing something in the wiring, but now I'm not sure about that either.

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We've checked all four available analog inputs, tried a different 0BA8, and tried every analog terminal on the VFD. 
EMI from nearby wiring has also been ruled out.

Everything else is working beautifully, but we're stumped on how to get an analog signal out of the ACS310.
It's always just this one volt noise.

IMG_20190228_103807.jpg

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You may have a bad output on the drive. Is there another analog output available? Do you have a 0-10V source you can wire to the PLC just to verify it's right (after disconnecting the drive, of course)?

 

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All of the 0BA8 inputs have been tested and will correctly register any regular 0-10V signal. 
Every analog terminal on the VFD produces the same noisy volt on our PLC. The frequency output from the VFD to the motor is optionally controlled by a potentiometer, which is working perfectly fine. We've tried hooking up to every leg of it and still get that noisy volt.
We've tried 0-10V terminals and 0-20mA terminals and it's always the same. 

Some connection must be missing, or incorrect... it's a stumper.

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What do you get when you measure the voltage at the drive's analog outputs with the PLC disconnected? Beyond that, I would need to dig into the manual for the drive, which I'm not able to do right now.

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It would appear that the VFD does not have an analogue voltage output , only a 0 to 20mA current output.

You can modify the Logo input to read current, or you could use a 500 ohm resistor to convert to 0 -10V.

 

Steve

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Is your connection cable correct screened?

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4 hours ago, Joe E. said:

What do you get when you measure the voltage at the drive's analog outputs with the PLC disconnected?

9V with the motor off and 21V with it engaged, that was without switching back to a more useful output configuration in the VFD (it was there because we tried them ALL)
They're not useful values, but we should be SEEING them when the PLC is hooked up to it, and we're not seeing anything but the Phantom Volt.

3 hours ago, nehpets said:

It would appear that the VFD does not have an analogue voltage output , only a 0 to 20mA current output.

You can modify the Logo input to read current, or you could use a 500 ohm resistor to convert to 0 -10V.

To my knowledge, the OBA8 analog inputs are just set to read 0-10V, although most analog function blocks can be configured to interpret 0-20mA.

More importantly, we also tried hooking our analog input to each leg of the potentiometer, and that IS running 0-10V. Still only seeing that Phantom Volt.

52 minutes ago, dekor said:

Is your connection cable correct screened?

Yes. Even without cable screening, though, we should still be seeing a noisy but controllable signal, instead of JUST noise.

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That's the parameters for configuring what that 0-20mA signal adjusts proportional to. As mentioned above, we've tried all of them... no luck there.

I'm not certain we're wiring the connection to the input correctly.

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If the drive's output is only 4-20mA, you're not going to get a good result wiring it to a 0-10V input without using a shunt resistor, as nehpets described. Can you reconfigure the PLC input to 4-20mA?

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The input cannot be reconfigured, although the software can compensate somewhat.
But we've gotten the same results hooking up to the Output Frequency Reference terminal, which is 0-10V.  

We have the appropriate resistor on the way, but without it we should just be seeing excessive voltage on the PLC input. Voltage above 10V just shows up as 10V in the 0BA8 (we tested that too). But nothing from the VFD shows any change in voltage whatsoever from that noisy phantom volt.

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The spec sheets for mA output modules I've looked at indicate that they can drive their signal through a short with no problems. For example, the Point IO output will drive 4-20mA through 0-750 Ohms. I would verify that the drive's output can do the same thing. If so, you can connect a mA meter directly to the output. If you get a good 4-20mA signal at your meter, then you will need to use a shunt resistor on your 0-10V input to get any meaningful readings there.

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