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Wiring Potentiometers in Series

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#1 Atlascycle

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Posted 17 October 2008 - 04:59 PM

I have an application where I need to control the spindle speed on a Coil Unwinding reel that has a DC motor and drive.

I would like to have a Potentiometer to set the max speed and then have another Potentiometer connected to a dancer arm that will increase the spindle speed as the strip raise the arm.

I am using a Baldor BC-142 Drive. Drive Manual

According to the Manual the Low connection of the Potentiometer is connected to terminal P1, the Wiper is connected to P2, and the High Terminal is connected to P3.

To Get this to work would I connect the Low terminals on Both Potentiometers to the P1 Terminal, connect the first Potentiometer Wiper to the High of the Second, Connect the Wiper on the Second Potentiometer to the P2 Terminal and the High of the First Potentiometer to the P3 on the drive?

Does this make any sense?

Thank you in advance for any Help.


Jason

#2 paulengr

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Posted 18 October 2008 - 07:01 AM

I have an application where I need to control the spindle speed on a Coil Unwinding reel that has a DC motor and drive.

I would like to have a Potentiometer to set the max speed and then have another Potentiometer connected to a dancer arm that will increase the spindle speed as the strip raise the arm.

I am using a Baldor BC-142 Drive. Drive Manual

According to the Manual the Low connection of the Potentiometer is connected to terminal P1, the Wiper is connected to P2, and the High Terminal is connected to P3.

To Get this to work would I connect the Low terminals on Both Potentiometers to the P1 Terminal, connect the first Potentiometer Wiper to the High of the Second, Connect the Wiper on the Second Potentiometer to the P2 Terminal and the High of the First Potentiometer to the P3 on the drive?

Does this make any sense?

Thank you in advance for any Help.


Jason



It is best to control dancers by measuring the TENSION on the roll as it comes off and using that to adjust your speed. This is not a problem that can be trivially solved with potentiometers and creative wiring. These are a bit tricky to do but if you google for it or contact a local automation company, you'll find plenty of information.

So I'll describe the various combinations of ways you can use 2 pots but be forewarned that pots are pots. You can't make it very linear and you might get lucky but mostly you are just going to end up with spooling everything onto the floor or breaking the roll by using pots.

Wire up the wiper to one side of one of your potentiometers, effectively shorting out half of it. This turns it into just a variable resistor. Wire this "variable resistor" in series with either the "high side" or "low side" of your other potentiometer. This causes the resistance of your main POT to become variable on one side. The effect you get is nonlinear but then again, pots are almost always somewhat nonlinear anyways.

Another technique is to wire the shorted pot between the wiper and high or low side contact. I think this is what you are trying to describe. How? Let's say you wire it up on the low side, providing a way to adjust the output voltage lower (reducing the low side voltage resistance). Say someone sets the "variable resistor" to 0 ohms, shorting out the low side. Now let's say they also adjust the potentiometer to maximum, effectively setting the high side resistance to 0 ohms. 0+0 = 0 ohms across the pot, shorting all 3 legs together.

In addition, things aren't very linear at all. Try simulating these various combinations in Excel using ohms law and you'll see all the craziness you will end up with.

#3 BobLfoot

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Posted 18 October 2008 - 05:31 PM

Its rather Old School but a simple LM941 Op Amp circuit would achieve what you desire.

Your first Pot for Max Speed would adjust the Hi Rail of the Op Amp, effectively setting the max output of the Op Amp back to the drive and hance the max speed.

Your second pot For Dancer Speed Adjust would adjust gain of the op amp, effectively increasing speed when the dancer moved.
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#4 Atlascycle

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Posted 31 October 2008 - 08:49 PM

Thanks for the replys. I got pulled away from this project, I think what I will need to do is add an arm connected to the Potentiometer to see how the coil is getting smaller as it is unwound. the only problem is that this uncoiler is double sided and I will have to have two arms and switch between them when the turrent is changed.

Thanks for the input on this.

#5 JeffKiper

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Posted 31 October 2008 - 11:06 PM

Jason
When I was in the same world as you we used evry kind of sensor you could think of to uncoil.

We used 1 photoeye to energize a clutch & de-energize a brake. They sucked because you always had a bang bang system.
Then we went to 2 eyes the first disengaged the brake and second enegized the clutch. They where stacked over each other. That was a little better because we gave the system a chance to freewheel to catch up.

We used dancers but what we ran into was the bounce of the arm on the strip was to much to control. So someone added weights to the arms to dampen the change in the that did help but then the feeder that was undersized to start had to work that much harder to pull the strip.

One of my favorite systems was the ultrasonics we had. There are several on the market that are made just to do what you want. We had some that you could adjust the signal dampening on so the responce was delayed and smoothed because of the strip jumping around.

Does your drive have 2 analog ins? If so use the first as max speed and the second a speed trim. I didn't get to use this machine but at a GE they had a long ramp to max rate on the drive. I guess (bad word) that they had the drive set do that once the line started the de-coiler would out run the line then shut off then start up and out run the line again. I do remember that it did not have any analog on it only discete.

In my current world we run our de-coiler at the same speed as the line. It would take some playing with but once you have you SPM you can figure up the FPM of sock that you will need. Set your Line speed in FPM and use your drive with dancer as a position control. Idea is if the dancer drops to the floor the drive slows down or if the dancer raises speed up the drive. You don't have any true tension control with a dancer.
JAK

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#6 atanas

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Posted 03 November 2008 - 05:16 PM

Hi Atlascycle,

I have used quite successfully similar Baldor drive and motor in similar application. The dancer mechanism was with ultrasonic sensor (as Jak suggested).

I do not think you need any additional elements. Look in the drive manual:

On the board you have four trimpots. Set the MAX speed a little over the maximum line speed and if needed adjust ACCEL and DECEL trimpots for smoot ramp-up/down the speed.


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