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Hi all, I am trying to set the frequency of an UMI VFD via the AO2 line of the snap-in I/O module (V200-18-E46B) connected to an V700 PLC, signal is 4-20 mA.

The VFD is set to get frequency value from AI2 input and the corresponding dip switch is correctly set for the mA input selection.

On the VFD, I set the P05.37 (Lower limit of AI2) parameter to 0400 so that 4 mA from PLC correspond to 0 Hz.

My problem is the range of values that the MI associated with AO2 output can be set to.

If I understand correctly, the MI = 0 correspond to 4 mA output from PLC so that the VFD should be set to 0 Hz.

Then for the maximum value I should consider MI = 4095 to set 50 Hz on VFD.

But there's something weird going on, VFD is at 0 Hz until MI = 8 and then starts raising and reaches 50 Hz before MI value reaches 4095.

 

What am I doing wrong? Can someone help solving this issue? Where can I look for an example on this topic?

 

Thanks in advance for support.

 

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4 minutes ago, Fotonic said:

If I understand correctly, the MI = 0 correspond to 4 mA output from PLC so that the VFD should be set to 0 Hz.

No, if you are outputting 4-20mA, then your MI would need to have a value of 819 to output 4mA. This assumes you have it set to "Fast Mode", which is 12-bit.

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7 minutes ago, Flex727 said:

No, if you are outputting 4-20mA, then your MI would need to have a value of 819 to output 4mA. This assumes you have it set to "Fast Mode", which is 12-bit.

I am pretty sure that the output from PLC is correct, measured current with a multimeter.

But anyway, since I am learning, how do I set fast or normal mode for the analog output of the snap in module? I cannot find anything related to this and in visilogic there's no setting for fast modes on AO configuration section.

Thanks a lot!

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6 minutes ago, Fotonic said:

how do I set fast or normal mode for the analog output of the snap in module?

Oops, sorry, that's for analog INPUTS, not outputs. The analog outputs for that module are 12-bit.

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29 minutes ago, Flex727 said:

Oops, sorry, that's for analog INPUTS, not outputs. The analog outputs for that module are 12-bit.

I see, so is it correct to assume a range 0 - 4095 corresponding to 4 - 20 mA 12 bit analog output or do I have to use 819 - 4095 range instead?

Tomorrow I'll try both cases and measure output current with multimeter.

But the problem remains on the VFD, I don't know how to achieve precise frequency control, considering I'd also like to use linearization function to set intermediate frequencies... :/

Edit:

Looking at the VFD manual maybe I found the problem. They say that AI2 0-10 V mode corresponds to 0-20 mA mode so that 10 V equals 20 mA. I set the parameter P05.37 (Lower limit of AI2) to 4 but if this is related to 10 V full scale then it should be set to a value of 2.  Then all the linearization made by the VFD should be correct too.

Edited by Fotonic
Update

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1 hour ago, Fotonic said:

I see, so is it correct to assume a range 0 - 4095 corresponding to 4 - 20 mA 12 bit analog output or do I have to use 819 - 4095 range instead?

It's 819-4095.

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You also need to keep in mind the input filtering that the drive itself is doing, which can influence expected results.  Any VFD control inherently has many settings on the VFD itself that need to be carefully fine tuned to match exactly what you want to achieve.  

And I'd also be revisiting your reference to P05.37.  What does 05.38 do?  There is more to all this than can be interpreted with my quick read of the manual.  It's likely all there, but my experience of VFDs is that they involve many nights of bedtime reading to become totally familiar with the unit!

cheers, Aus

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Along with all the checks above you should also check the way the signal is wired.

If the inverter needs a passive signal then you must connect the inverter 4-20ma common to the  PLC 4-20ma commom (0v).

However many inverters need to see there own powered loop. In this case you need to wire as an active input.

The fact that the inverter rises rapidly from min to max frequency with such a small increase in the MI value suggests a "clash" of voltages.

Regards

Denis

 

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Denis above touches on something I had assumed was in place correctly re the commons.

A side issue to this is that I always try to ensure that every piece of control gear across a site is running from the same phase.  Given the very light loads control gear do, it is a virtually insignificant imbalance and is easily adjusted if necessary. 

On most 3 phase equipment where it isn't immediately obvious (hidden inside casing etc) and a neutral is part of the connection, the control one is often easily found by there being a protection device/fuse etc which can be easily tracked to one of the inputs.

cheers, Aus

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Please note

P00.06 - sorce A frequency command selection

P00.07 - sorce  B frequency command selection

P00.09 Combination of the setting source    -  it is need to be correct configured.

Maybe you use another setpoint sorce.

Also check P00.01 run command channel.

 

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So, the P00.* parameters on the VFD are correct, commands are received via the digital inputs on the VFD itself and the frequency is set via the A2 analog input on the VFD, the dip switch for V/I selection is set on I (at least I hope so, unitronics documentation lacks this information... pretty bad... :/ ) and the analog output from PLC is outputting the correct mAmps.

Connections are made according to unitronics VFD manual.

No success so far, I'll try some more experiments with VFD parameters and in case change to 0-10 V input signal to see if at least that works. :/

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Running a VFD from the PLC should not be this hard.

I reading that you are unsure of your electrical signal.  It's time to back up and verify what you're doing.  A meter will be required.

First, I personally don't like to control drives with 4/20 because it's hard to verify what's going on without breaking the circuit.  The drive is often in the same panel as the PLC, so 0-10V is much easier.  Most drives come configured that way from the factory.

Change your PLC program and hardware to a 0-10V signal and then put your meter on it while you change the value in the PLC.  A value of 0 to 4095 should give you the expected 0 to 10 volts out of the analog module.  This should give you some direction as to where the problem is.

Joe T.

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10 hours ago, Joe Tauser said:

0-10V is much easier. 

+1 to this.  Unless I am using a proven device I know backwards that also gives me an easy way of checking things via any method of monitoring, I always use 0-10V for exactly the reasons Joe states.

Aus

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20 hours ago, Cam said:

The jumper setting are in the installation manual.

 

 

Yes, PLC jumpers are documented, the mistery is on unitronics VFD switches.

With a torchlight one can see inside VFD and near the switches there are some "V" serigraphed, but it's not clear how to interpret them.

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20 hours ago, Joe Tauser said:

Running a VFD from the PLC should not be this hard.

I reading that you are unsure of your electrical signal.  It's time to back up and verify what you're doing.  A meter will be required.

First, I personally don't like to control drives with 4/20 because it's hard to verify what's going on without breaking the circuit.  The drive is often in the same panel as the PLC, so 0-10V is much easier.  Most drives come configured that way from the factory.

Change your PLC program and hardware to a 0-10V signal and then put your meter on it while you change the value in the PLC.  A value of 0 to 4095 should give you the expected 0 to 10 volts out of the analog module.  This should give you some direction as to where the problem is.

Joe T.

I'll discuss with my superior to see if it's ok to go with voltage control, in that case I hope it will be more immediate and the I control will be experimented again in the future, sadly I have no much time left to dedicate to investigate this problem.

I don't know what to do with VFD, all settings seems ok to me, followed manual indications where present.

PLC is outputting the right mAs, as expected.

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Remember me saying that VFD manuals need to be completely read!  The switch settings look clear enough in this, but perhaps they are physically hard to find.  Haven't handled one in the flesh.

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cheers, Aus

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36 minutes ago, Ausman said:

Remember me saying that VFD manuals need to be completely read!  The switch settings look clear enough in this, but perhaps they are physically hard to find.  Haven't handled one in the flesh.

 

cheers, Aus

Trust me, it's a pain to understand how those switches need to be set.

The serigraphy near the switches reports something like "V/I" on one side and the switches are soldered so near to eachother that it's impossible to see if there are other writings on the other side of them. The VFD I am working on at the moment is relatively small (1.5 kW 1ph).

Last month I had to work on 2 VFDs of 15 kW size and accessed the switches just to set RS485 termination on the last one on the bus (I could use modbus on that project and all went ok at first try), I admit I don't remember how the switches were placed but I remember that was not so immediate to locate the correct setting for the RS485 one I needed.

I have 2 7,5 kW VFDs around now too, time to have them installed and I'll have a look at the switches... if possible I'll take and post a picture, stay tuned. :)

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Voltage control is simpler and easier to measure online.

However if you have the switches set to "I" and the correct output from the PLC, there should not be a problem with current.

Can you post a quick sketch of how it is wired up?

Are you using the 24v of the VFD or the 24v on the PLC supply?

Dont worry about the dip switches in the snap in module, these are for analog inputs and not the outputs.

Regards

Denis

 

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Wondering if the switch position shown is a bit like some of the other plc install instructions, in that the black and white are not really well explained, so you don't really know which way is correct.  Joe posted about this conundrum here:

Perhaps worth a look.

cheers, Aus

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@Cara Bereck Levy

Cara, given that Fotonic is having issues and that the UMI VFDs seem to be "typical" with the myriad settings available, perhaps it would be a good idea if you changed the  "Quick Start" in the manual to essential fundamentals, that does good explanations of how to do a basic hookup and get the thing running in no time at all. 

cheers, Aus

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