Frequency Control of a VFD by HMI

I want to operate a motor by VFD by a plc and HMI. The motor is operate with 4 or more step by change terminal connection. It is easy to me, but i need to control frequency by HMI in any step. But i can't use Analog module an any potentiometer. Is it possible? I want to do this using Mitsubishi Fx 1N 60MR PLC. can anybody help me?

If I understand you correctly you should be able to use some logic in your plc that is driven by selections made on your HMI to fire different outputs that select multiple preset speeds on your drive. Unless you can write parameters to the drive from your screen then these speed values would be fixed unless you change them on the inverter keypad.

Actually I want to change the frequency of any step of preset value by using HMI. May be it can be pulse control ladder. Because i want to macke a small machine, which is operated with 4 steps. There are some preset value will be set like Step1: 20Hz, Step2: 30Hz, Step3:35Hz, Step4:50Hz. but whwnt the machine is running with Step2 iwant to change the speed by HMI. But the step is Same. Can anybody help me

If you want to be able to actually change the speed for each step to any value you want (i.e. not a preset programmed into the drive) without using an analog output module, then the only way I can think to do this effectively is with a comms bus connection of some kind, i.e. MODBUS.

I did come across a setup once with an old PDL drive where 8 digital outputs on an RTU were being used to control the speed by encoding that speed reference into 8 bits which the drive then decoded back for its reference. That particular drive had that as an option, not sure i've seen that on modern drives.

Good luck...

Which VFD are you using? Some of them have Pulse inputs, or you can try to make/buy a signal conditioner that will take your pulse-train output and turn it into a 0-10V signal.

One of my colleagues has used the iPos program in an SEW Movitrac to write his own Pulse to frequency code in the past. This uses a standard digital output.

if you know how to program the HMI and MIT Plc,

it's easy for members to give an idea,

but if you don't know, it will big problem

Hi Most drives have hard wired connections for different speed selection (speed usually set by a parameter)

So
Preset speed 1 maybe 20Hz
Preset speed 2 maybe 30Hz
etc

At the HMI you can have a button for each step to provide a plc output binary pattern for your drive preset speed inputs

For most companies that make both VFDs and PLCs, the easiest approach will be to use the same brand for both, there will be very simple interfaces to do what you want to do. So in your case if you want to use that Mitsi Fx PLC, talk to your Mitsi supplier to get a Mitsi VFD that has compatible communications options, then get the HMI that goes with it as well. You can do it without that, but you will be on your own to create comm messaging back and forth, and given that you had to ask the question in the first place, that indicates you are probably a novice. For a novice, brand compatibility is a better place to start.

Thank u Jev, i think u r right. by using pulse train it can be possible. can u give me any more idea about it?

You have a few options here. You can either use your Output to generate a Duty based signal, a Frequency based signal, or use a couple of outputs and write your own serial with a data and strobe bit.

Frequency:
There are several methods to write code that generates a pulse on your output (Pick one!). Try to make it as accurate as possible keeping scan times in mind. Your processor and output hardware will limit the range of this frequency, for example 0-1kHz. Use a configurable Frequency to Analogue converter to generate a 0-10V or 4-20mA signal for your drive. Since you're not changing the frequency that often, or quickly; the reaction time isn't critical. I would use something easy like 0-200Hz and scale it 0-10V, so you have a little resolution to play with. It won't be perfect, but it will be usable and you can adjust it to suit.

Allen Bradley 931S-F1C2D-DC
http://raise.rockwellautomation.com...ents.asp?CID=ABEEC947E096459E9EBD163EC2422A7C

Phoenix Contact MCR-F-UI-DC
https://www.phoenixcontact.com/online/portal/us?uri=pxc-oc-itemdetail:pid=2814605

Many brands have similar items.

Duty:
You'll need a VFD with programming capabilities. I know SEW and ABB have drives like this. Create a task in your PLC program that's scanned every 2-50ms (Depending on how quickly you need to change things). Within this task create a counter from 0-100 (0-100% of that period). Turn the output on from count 0 to any upper limit <100, and this will give you a duty. For example 0-50 is 50%, and so on. Write a routine into your drive that uses the same known period (2-50ms) and measures the on-time of the input. From that calculate your duty % in the drive and scale your speed. This won't be entirely accurate, as you'll use up some time in counting/timers. You can use an error correction to fudge this.

Serial:
Again you'll need a VFD with some programming capability. Chose an appropriate clock (I think we've used 50ms). In both your PLC and VFD programs write code for 2 outputs/inputs (You can use more to make it less complex). One is your data bit and one is your strobe bit.

- Hold the strobe bit high for a time longer than your clock. That way the routine in your drive knows this is the start of data transmission.

- Once this goes low, count and strobe your data through the outputs. Every clock cycle is a bit of data you want to shift. I think we currently shift 64 bits, or 2 DINTs. The more you shift; the longer it will take. Just be careful how you use rising/falling edges to strobe and when your data bit changes in relation to your strobe, or you can get some timing issues.

- In your drive write a separate routine or function for the data transmission. When you see the long strobe, it means data is about to transmit from the PLC.

- As the strobe toggles, shift the data bit into a word in your drive and increment a counter.

- When the counter hits the number of bits you're sending (64 for us), check that the data makes sense and then use it to change the drive speed.

- If the counter doesn't reach the number of bits, or the data isn't within acceptable limits, then get ride of it. As an option you can send an output back to the PLC asking for the data again.

Maybe I'm being dense, but if all you want to do is change the preset values why can't you simply use the keypad that comes with the VFD?

You may be able to do this with an HMI and a VFD that both talk Modbus. Then just set the various HMI elements to the equivalent Modbus registers on the drive. I've never done this, but something like a C-More from AutomationDirect and a Powerflex 523/525 might be a decent solution.

Otherwise, a lot of drives come with remote-mountable keypads. Why not just do that like Tom suggested?

The posted probably need to run the VFD speed in manual mode if the auto mode system fail or initial during startup.

He probably expecting using Plc DO via relay act as binary input,configuration on VFD Digital Input parameters.

e.g
Relay no:1 ON - 0001 – 10hz,
Relay no:1 and no:2 ON - 0011 – 20hz,
Relay no:3 ON - 0100 – 30hz,
Relay no:1 and no:3 0101 – 40hz,

From the HMI,
4 command PB each assignment with selecting speed.

From my understanding; the OP currently has DO's changing the preset frequencies on a drive. With this setup, if you wanted to vary the speeds, you would need to continually adjust the preset parameters in the drive.

What they're after is something you can adjust from the HMI, without the use of added analogue cards or fieldbus... So rather than using presets in the drive, you enter a value in the HMI that allows you to change the frequency (Full range) through the PLC program.

The usual way to do this would be analogues or fieldbus, but I suspect it's an existing system that no one wants to upgrade or spend money on, but want the functionality of being able to adjust the speeds from the HMI, rather that having to play with the drive.

Jeev said:

From my understanding; the OP currently has DO's changing the preset frequencies on a drive. With this setup, if you wanted to vary the speeds, you would need to continually adjust the preset parameters in the drive.

What they're after is something you can adjust from the HMI, without the use of added analogue cards or fieldbus... So rather than using presets in the drive, you enter a value in the HMI that allows you to change the frequency (Full range) through the PLC program.

The usual way to do this would be analogues or fieldbus, but I suspect it's an existing system that no one wants to upgrade or spend money on, but want the functionality of being able to adjust the speeds from the HMI, rather that having to play with the drive.

Click to expand...

The classic "I want a brand new luxury car, but I don't want to spend any money" problem.