GS1 Drive Max Speed...

I asked this question over at the A-D forum, but the response time 'round here is much better...

When using the front panel potentiometer to control speed on an A-D GS1 drive, is there a way to limit maximum motor speed?

IOW, "scale" the pot?

Right now, it gives 0 to 60Hz, but I want to change the range to something like 0 to 30Hz to prevent some bozo from accidentally exceeding the mechanical capabilities of the machine it's driving... bonkhead

I know you can scale the analog input, but I'm not sure if there's a way to scale the 'on-board' pot. Worst case is I'll throw an external pot on the thing, but that seems stupid since there's already one just sitting there...

Any ideas?

beerchug

-Eric

Eric I dont know the drive but could you use the motor parameters 02 03 and 04 to set the frequency and/or rpm to half the rated?

Just curious, have you tried the offset in parameters 4.02?

It is unusual they dont state a maximum/minimum frequency setting, maybe we are overlooking the obvious.

For those interested one manual for a GS1 is here:
http://www2.automationdirect.com/static/manuals/gs1m/gs1m.pdf

Yes, overlooking the obvious. That's what I was hoping for... ...No such luck...

You can only set the base frequency to 50, 60, or 400Hz, so no trick there. As far as changing the motor base RPM and max RPM, I'm not sure I want to fiddle with that as I'm not positive that it won't damage the motor... utoh

Since the manual states that the base RPM can be set from 375 to 9999, I question why there's a limit on the low end (375). IOW, what if someone wanted a max RPM of 300?

Parameter 0-04 (Motor Maximum RPM) is where I'd expect to set my max RPM (kinda good description!), but that can only be set from whatever the base RPM is, to 9999RPM.

I did try setting the 4.01-4.04 parameters. This had no effect on the pot.

I have a feeling that they didn't include parameters for a scenario like mine, so it just can't be done. Oh well, I guess you can't have EVERYTHING when you only have to pay US$168 for it...

I think I'm gonna experiment with selecting the speed over MODBUS. Then I can just set my limits in the PLC...

Thanks for the effort, Ron!

beerchug

-Eric

AHA!...

I just found something that works!...

No exactly what I wanted, but not bad.

In the Protection Parameters (6.x), there is a parameter called "Upper Bound of Output Frequency". I set that to 32Hz (the max value I want), and the drive will not go above that setting. The bad news is that the potentiometer 'resolution' doesn't change. You still have the same control up to just over 50% on the dial, then it has no effect beyond that.

This will be okay for this application. It should keep the idiots at bay, which is all I'm concerned about. Although, I'll probably still toy with the MODBUS idea if I have time...

beerchug

-Eric

Eric, I scanned thru the instruction manual rsdoran posted and have the following suggestions.

When the parameter is asking for motor nameplate data, enter it just like it is imprinted on the nameplate. This is not the place to attempt max or min speed limits. You can get into motor trouble if these are not entered accurately.

The overall max and min frequencies in Section 6 of the parameters can be used to limit speed regardless of which input source is in control. However, as you found, you can end up with deadband on top and bottom of the sweep.

If you look in the manual at pages 4-32 thru 4-34, there is a discussion about adjusting the speed input gains. I believe that this is where you can tune the sensitivity of your speed pot. For example, if all you want is 30hz maximum, then I would start with an analog input gain of 50%. You may need to tweak this to get exactly what you want on the bottom and top.

One little suggestion here. I really hate to see drives programmed for 0hz at minimum speed. There is a huge difference from a safety standpoint between 0 speed and stop and it is hard to tell the difference when looking at the motor. At zero speed the motor is energized, and anyone coming into contact with the motor leads will be at considerable risk from shock. Whenever the process will permit it, leave at least 1 or 2 hz on the bottom of the speed reference so there is a clear difference between minimum speed and stop.

DickDV said:

Eric, I scanned thru the instruction manual rsdoran posted and have the following suggestions.

Click to expand...

Good, I was hoping for your input!...

When the parameter is asking for motor nameplate data, enter it just like it is imprinted on the nameplate. This is not the place to attempt max or min speed limits. You can get into motor trouble if these are not entered accurately.

Click to expand...

I though so... That's why I said I didn't want to fiddle with that. Thanks for the confirmation.

The overall max and min frequencies in Section 6 of the parameters can be used to limit speed regardless of which input source is in control. However, as you found, you can end up with deadband on top and bottom of the sweep.

Click to expand...

Yes, "deadband"... That's the word I was looking for!
Looks like this is my only option with this drive...

If you look in the manual at pages 4-32 thru 4-34, there is a discussion about adjusting the speed input gains. I believe that this is where you can tune the sensitivity of your speed pot. For example, if all you want is 30hz maximum, then I would start with an analog input gain of 50%. You may need to tweak this to get exactly what you want on the bottom and top.

Click to expand...

I tried this last night, but it has no effect on the on-board pot. It seems these parameters only affect the analog input. If I mention this to A-D, I expect they will add this ability in the future. They've been very good at fulfilling "wish lists" with their other products!... :nodi:

One little suggestion here. I really hate to see drives programmed for 0hz at minimum speed. There is a huge difference from a safety standpoint between 0 speed and stop and it is hard to tell the difference when looking at the motor. At zero speed the motor is energized, and anyone coming into contact with the motor leads will be at considerable risk from shock. Whenever the process will permit it, leave at least 1 or 2 hz on the bottom of the speed reference so there is a clear difference between minimum speed and stop.

Click to expand...

This is an excellent point to bring up. I am always looking for good ideas to make a process safer (and more idiot-proof, but that's never easy!). Yes, there should never be a need for a zero speed setting. If you want zero, just turn it off!...

Thanks again for your input... It's much appreciated!

beerchug

-Eric

One last thought here, Eric. I'm not familiar with how these drives are laid out but, would it be a major undertaking to lift the wires on the existing speed pot and rout them to the analog input?

I've only used a half-dozen or so of these drives so far, so I haven't had a chance (or need) to peer "under the hood" (YET!). From the looks of it, I have a feeling that the pot is soldered directly to the main PC board (or possibly a daughterboard). This is a fairly compact drive, so the pot connections might not even go through the board (surface-mount technology)...

For now, I think using P6.15 to limit the max (AND P6.14 to limit the min, per your suggestion) will do. There is no need for 'fine' adjustment of the speed. I have a feeling the drive will just "live" at the max speed setting anyway...

beerchug

-Eric

Eric,

If you do talk to AD, you might suggest that they look at the following idea...

  MIN            Speed Pot            MAX

   |                                   |

   +-----------------------------------+



   +-----------------------------------+

   |                                   |

   0%    Analog Input for Scaling     100%

If the Analog input is at 100% then full scale of the speed pot is 0-60.

If the Analog input is at 50% then full scale of the speed pot is 0-30.

If the Analog input is at 25% then full scale of the speed pot is 0-15.

The Speed Pot adjustments should then develop better resolution as the Analog Input Signal goes down. That is, 100-steps/60-Hz, 100-steps/30-Hz and 100-steps/15-Hz. The lower the analog signal, the lower the value of each step.

This basically the idea of a Master Speed Control. You can then keep that analog pot hidden somewhere.

ABB uses this in their drive control... you just have to select whether or not you want to use that scheme.

Nice idea Terry!... You could also use a fixed value resistor in lieu of the pot.

A quick update to Dick's excellent MIN speed suggestion...

I implemented this, and THOUGHT it worked. I set MIN speed to 10Hz, then turned the pot down. Sure enough, it quit reducing speed near the CCW stop. But then, when the pot actually reached the stop (0%), the drive went to zero speed. Similar to an on-off/volume control on a cheap radio, but without the "click" to off.

This sucks, as you can still get the drive to "run" at zero Hz. I think I'm going to scrap using this on-board pot altogether. I'll just add an external 5K pot which I'll be able to make work the way I WANT it to!...

beerchug

-Eric