VFD Switch on Frequency

No matter what the frequency is when I switch the VFD off it always defaults to the highest frequency when I switch it on.

Am I missing a setting.

Have not specified my model as just want some feedback from other VFD users

I am useing the frequency control knob on the VFD to set the speed not an optional pot

Edited By petro1head on 12/12/2019 13:02:55

The front panel knob may be an encoder rather than a pot (to sense rotation, not absolute position). The smaller Schneider VFDs are like that for example. In that case the VFD only knows the knob has rotated 'so many clicks, plus or minus from starting point' - At power off the position will be lost unless of course there is a parameter setting that can retain the position/frequency.

A 'start up frequency' may have been set.

Best thing to do is check the manual carefully for the precise model, different brands/models have different capabilities. If it is a mainstream brand, try calling their technical support line or drop them an e-mail.

Check your minimum and maximum speed settings in the VFD config

I think David has the answer. Indeed its probably a rotary encoder and not a pot. So I will have to buy a pot.

Stuart they are set correctly, just checked thanks

Edited By petro1head on 12/12/2019 16:44:05

I have only used the rotary encoder to program the VFD, as I had already connected all the remote controls. The speed is controlled by a pot which has to be programmed and certainly always sets whatever speed the pot is at when the start switch is pressed. The encoder does not have travel limiting stops like a pot.

Defaulting to max. speed on switch-on isn't a normal feature of the VFD fitted with a rotary encoder that I have, a Schneider. It re-starts at the previous speed setting after being switched off at the mains. The same applies to my other VFDs with pots. unless the pot. has been twiddled  whilst the VFD was off.

Somewhere in the parameters should be one controlling the working frequency source. It's worth checking that it's set for panel control rather than, say, external or PC.

Edited By Clive Brown 1 on 12/12/2019 19:56:19

Interesting.

These are the options under Frequency Setting Mode:

0：Frequency setting（UP/DOWN）
1：Panel potentiometer
2：External AI1
3：External AI2
4：PI regulation
5：UP/DOWN by the P5-20 add and subtract
6：UP/DOWN by the P5-20 add and subtract, frequency qing zero downtime

I have it set to 1

Not sure what option one is about as there is no Up/Down

Edit: Just set the option to 0 and now it remembers the last Frequency setting.  Not very intuative if you ask me but not complaining if it works

Edited By petro1head on 12/12/2019 20:31:47

That's logical:

• Option 0: Rotary encoders detect right/left movement not position. As encoders only signal turning steps the VFD controller has to set and remember the frequency in software. Then the controller converts right/left rotary clicks into up/down frequency steps relative to the frequency it stored in memory.
• Option 1: A potentiometer returns a voltage directly related to it's physical position. The controller derives frequency straight from the voltage and has no need to remember anything in software. In effect, the potentiometer is the memory.

Selecting option 1 told the controller it had no need to remember frequency. But you're right to say this behaviour is somewhat counter-intuitive. It would have been more user-friendly had the controller been programmed to ignore the rotary encoder when Option 1 is selected (and vice versa). Maybe there's a Use Case where it's handy to set the frequency with a pot and then to vary it with the encoder? Don't see it myself!

Trouble with potentiometers is their tracks wear and go intermittent, especially in a dirty workshop. Sooner or later, even the best have to be replaced. Encoders are a good deal more robust, but the controller has to be brainy enough to understand them. Not a problem now that microcontrollers can be had for well under a pound: very common today to find electronic controls implemented with rotary encoders rather that pots.

As an aside, rotary encoders come in two main families. Most common are a cheap plastic type with low resolution (perhaps 20 counts per revolution), low turning speed, and click detents . These are intended for manually operated controls. Also available are precision encoders, about 25x more expensive, with high resolution (up to 2000 counts per revolution) and capable of spinning up to about 3000rpm. This type is used for precision control or precision monitoring, as needed to make an Electronic Lead Screw.

Dave

That's puny...

www.renishaw.com/en/resolute-absolute-encoder-system-with-rexa30-rotary-angle-ring--10852

32-bits, 36,000 rpm...

Neil

I tried a pot on it today, had to set it to option 2, much better as I now dont had to twiddle as much

So ordering a new 5k Pot with knob and fabricating a bracket

Want one!

"Contact for quote" I see. That usually means big money, but it is xmas and I've been a good boy all year. I'm sure fellow forum members are desperate to know what to put in my stocking this year. Problem solved!

Dave