Running VFD using preset speeds + Potentiometer

[powersoff]

I would like to run a conveyor motor at 4 different speeds. 3 of the speeds would be hard values (parameters entered based on digital inputs). The 4th speed would be from a potentiometer and would need to take precedence over the digital inputs . I have a Yaskawa drive to work with and have been told by customer this should be simple (no plc control wanted). Has anyone successfully implemented a similar scenario?

 

[jraef]

Not a big deal. Set up a 4 position selector switch, with 3 contacts that close in one position each, with the 4th position having all 4 contacts open. Program the VFD to be in Pot control as long as none of the speed inputs are closed, then program the preset speeds to respond to contact closures from the switch as it is moved to each position.

 

[DickDV]

jraef, I think you misread the OP. I sounds to me like the idea is to have the speed pot take presidence over the fixed speeds.

powersoff, I don't think you have a complete picture of how the speed pot is to take precedence. You will need to provide something somewhere which selects the speed pot over the fixed speeds because there is always an output on a pot.

You could use a selector switch which selects either the pot or the fixed speeds but that gives equal precedence to both modes.

If your drive has level detection capability on the output relays, you could set up one relay to pick up only at the bottom of the pot's rotation and then powering the fixed speeds thru a normally open contact on the relay. That would give the pot precedence at all rotation positions above the minimum point. The operator would have to turn the speed pot down to minimum to get the fixed speeds to work.

I'm not sure I'm helping you any here. Are we understanding you correctly?

 

[powersoff]

DickDV,

Yes,
I think you understand and No I don't have a clear picture of how the speed pot will always have priority.
The ideal situation is the operator will not have to use pot. The conveyor will change speeds via digital inputs (photo eyes) but I think the real world is going to interfere and it will be necessary for operator to change speed as needed via the pot.
I will have to look in manual to see about level detection capability.

 

[davidbeach]

Actually, I think that jraef has it nailed quite well. If it is done otherwise where the speed pot takes priority then what will happen is that all of the speed settings will be what ever they were last adjusted to by the pot and none of them will be the original presets.

 

[ozmosis]

As you have a Yaskawa drive then the probability is that you can set a parameter to provide what you are looking for. However, as you have a Yaskawa drive, you will need a PhD in Egyption hieroglyphics to understand the manual. This is not knocking the drive (they are very good) but their manuals are notorious for being rather complicated.
It would help if you advised the type of Yaskawa drive and this may prompt someone who has used this feature before to advise.
As an example, I know the E7 can do it but I couldn't for the life of me advise correctly the parameters to set to ensure the drive will see the Analogue input and Digital pre-set speeds without changing a parameter value.

 

[powersoff]

The model # is GPD 305/J7.
Thanks.

 

[DickDV]

Fellas, I have no desire to be argumentative here but the OP clearly says he wants the speed pot to take precedence over the fixed speeds.

In every drive I've ever seen, the fixed speeds take precedence over the speed pot.

I don't see a really simple way to do that.

 

[bklauba]

Would not 3 N.O. relays, each enabling a different fixed speed, and the pot, do the trick? This way, the pot has precedence, but energizing of any of the relays causes the VFD to run at that preset speed.

BK

 

[jraef]

That is essentially the same as what I said, just substituting relay contacts for switch contacts.

powersoff,
DickDV is right, my solution, though simple, is not exactly what you wanted, but it is a lot easier to implement for a novice.

But from your subsequent description of the application, I actually see now that you want to be able to TRIM the speed with the pot once a preset speed has been selected. That is subtly different.

I could do it with several other drive mfrs' products so I'm sure it can be done with a Yaskawa drive, but I have to agree with Ozmosis, the Yaskawa manual can be daunting for the uninitiated. Years ago when Magnetek was brand labeling the Yaskawa drives, they completely re-wrote the manual, making it clear and easy to understand. I preferred the Magnetek version solely for that reason. But alas, that situation no longer exists; now everyone is relegated to that horrible manual translated directly from Japanese.

The way I would do it would be to set up the contact closures as separate minimum speeds, but the pot is always the ONLY speed command reference. So for instance, if Speed 1 is 20Hz and you want to trim it to somewhere between 18 and 22 Hz, set up Input 1 to change the Minimum Speed to 18Hz, then let the Pot trim it within that range.

Some drives will give you full access to all I/O and command programming so that you can do this, others may involve setting up 3 completely different parameter sets and using the inputs to switch between them. I don't have that Yaskawa manual to tell if either is possible, but that should give you a direction to head.

 

[ozmosis]

As the drive is the J7, it may not be a easy as originally thought. The J7 is the low feature range and may not provide the functionality required. I had a quick look on the manual of the J7 and it would appear the use of multi-speed inputs and AIN is not directly possible as the drive needs to be setup for either digital input as the speed reference of AIN as speed reference.
It may be possible to use 3 digital inputs as your multispeed seeting and use a 2-wire configuration on S5/S6 as a means to provide a "raise/Lower" function via a couple of push-buttons.
However, I would play around with it to find out as the more I looked at the manual the more I found out where King Tut's grandfather was buried..;-)

 

[roydm]

How about using strictly analog control with trimpots for each of the fixed speeds and a relay to select each one based on the photo eye.
Presumably the operator would throw a switch to take control i.e. drop out whichever relay is closed and substitute his manual pot.

That might work

 

[waross]

I think that we need a better description of what we need.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[powersoff]

My goal is evolving and on top of that all communication at this point has been verbal.
So far the idea is...
1. Push start button VFD starts conveyor at the idle speed.
2. If first photoeye on (run at low speed).
3. If second photoeye on run at high speed( at this point high and low photoeye are on).
4.If high photo eye drops out deaccel back to low, If low photo eye drops out deaccel back to idle.
5.If at any time operator not satisfied with speed he will adjust pot to his liking.

I did find a up/down parameter in the drive manual but if both up/down inputs on or off drive holds speed.

 

[roydm]

OK, I think I see now, The Highest speed takes over, and if the operator doesn't think it fast enough then he can boost the High speed.
How about this.
3 different potentiometers Idle, Low, High all with their ccw tab connected to 0V or common.
The Idle speed pot cw tab connected to the speed reference supply voltage (I will refer to as +10)
The Low speed pots cw tab connected to +10 thru the Low speed photo eye
The High speed pots cw tab connected to +10 thru the High speed photo eye
Each pot's slider tab connected thru a forward biased diode to the speed reference input.
When the drive starts it receives set-point from Idle pot thru the forward biased diode.
Low speed photo eye closes, because it's pot setting is higher its diode takes over.
High speed photo eye closes, because it's pot setting is higher its diode takes over.

Give the operator access to the High speed pot or provide a 4th potentiometer powered thru an override switch. The problem with the latter, he/she must remember to open the switch again unless you have it reset once the high speed photo eye clears.

A few minor points.
If the speed doesn't drop from High to Low you may need a bleed resistor e.g. 100K between Reference and 0V
The highest speed would be with pot fully cw -0.6V
Use a resistor in series with the speed pots to reduce their range.
Be careful not to overload the drives speed reference voltage source or perhaps use a separate regulated supply.
You could also string the pots in series with the photo contact in the slidewire circuit or use change-over contacts from the photo switches to eliminate the diodes.
Don;t run the speed reference voltages with power wiring unless it's shielded, if the photo switches are far off it would be better to use interposing relays.
The drives Start/Stop inputs are normally low voltage DC, if so its OK to run those with the speed reference.

BTW the diodes are called Auctioneer diodes, the highest bidder gets it.

Roy

 

[intoxicated]

if the 3 speeds are hard values (don't know the Yaskawa drive's inputs), why not use real resistors (reflecting the actual fixed speeds) in series with, and switched by a relay/digital output, and switch to pot when you need it, you can switch the 4 values, 3 of them fixed value, and the 4th actual value of the pot, and you'd only need the analog input