Using a Reliance Master Control with GV3000 Drives

[ssommers 20]

This project landed on my desk & I haven't done one of these before so I have a couple of questions. I have 8 GV3000 drives controlling individual motors on a tube mill. They all run at different speeds that gradually increase from #1 to #8 in order to draw the tube down to the proper diameter. The rolls on each motor stand are changed frequently (at least 5 times per week) as the tube size requirements change or as the rolls get worn and have to be replaced. There's no PLC controlling this tube mill - it's all relays & drives. They tried teaching the operators to change the parameters, but that didn't work too well so the electricians have to change the parameters. So... about 5 years ago, someone bought a Reliance Master Controller, but it was never engineered or installed for many & various reasons. Now management wants it installed this week because the mill is down for other upgrades. The book says nothing using this with the GV series drives. I'm hoping that's simply because the Master Controller is older than the GV series. It looks to be a big pot that controls the incoming 115VAC to the transformer that steps down & converts the signal to 0-12VDC that is distributed to all the drives. Then that signal gets hooked to another pot at each drive to be able to tweak the final setting. Is anyone else using a Reliance Master Controller to distributed drives? Is there anything else I need to consider before hooking this up? Thanks in advance! Susan

[GerryM 2]

All the master controller does is supply the overall speed reference to the line. If your GV3000's are setup to operate with a voltage reference(0-10V) then it should work. The more important question is will you still have to adjusty the trim between stands #1-8 for every setup change? I assume 'yes' since different tooling usually equals different operating characteristics. So in the end how is that different than what you are doing now? I think you need to go back to the engineering stage, as you said here: "it was never engineered ". As an example: Your GV3000 may be able to be networked and controlled that way. Maybe its better maybe not, but i would say the whole thing needs to be engineered to find the best solution. Is this the unit you are referring to: http://www.reliance.com/pdf/drives/instruc...20controller%22

[ssommers 20]

Yes, that's the one and I'm definitely doing the engineering stage. I'd rather take an extra week now than to slap it in and have management come back and say "That's not what we wanted," even if they're on my case to have it done. Right now, the drives are setup up in series. Only the 1st drive has a speed pot and there are no encoders on any of the motors. The 1st drive sends an analog output to the 2nd drive which has a gain parameter set to about 1.05. The 2nd drive sends an analog output to the 3rd drive & so forth using the gain parameter to control the speed on the next drive. This requires an operator (or more often, an electrician) to know how to change the parameters whenever a sizing roll is changed. And worse yet, it can't be a predictable gain number because the sizing rolls may be ground down about 1/2" in diameter over their lifetime. It's a case of you never know what speed you'll get until the operator puts a tachometer on the top of the roll. Add to that variability that the gain ratios between the rolls are never the same for any 2 sizes of tubes and you have a real mess. My first thought, when I saw the setup, was to put an encoder with a 1 ft. wheel on the top of each sizing roll. Feed that back to the drive & then it would be easy to set the speeds with an individual pot. The problem - too much fluid spraying in the sizing section which would either make the encoder wheel slip or gum up. Inconsistancy in the encoder will cause inconsistant motor speed will cause inconsistancy in the tube. Not good, so I had to rethink it. Now I'm looking at this Master Controller and realizing that the best thing about it is that the drives will be independant. I'll be able to set all the gains at 1. No more electrician calls because the operator will be able to turn a knob to change the speed. And if the operator only has to change 1 sizing roll because it's worn down, he'll be able to simply tach that one new roll during setup. No more running through the whole set of 8 just because 1 changed. The larger problem is that I'm going to have to explain to management why I'm going to spend money to go from 1 pot to 9. The pot on the Master Controller will set the fastest motor's speed regardless of which drive it is. All the rest will have their speeds trimmed down using their individual pots. I'm certain that management will see this as stepping backwards, but I'm going to push that it's more flexible & user friendly than their current system. Thanks for helping me think this through, Susan

[GerryM 2]

That does sound better. Glad to see its coming together. I also have a tube mill. It has three sections with three DC motors and three old reliance drives. Each motor drives 3-4 stands interlocked through a transmission. We have only two trim pots and a master to worry about. We don't have the master controller, I think each drive accepts a master and trim signal somehow. I'm not sure what the procedure is for adjusting them, I know they use an ampmeter to assist there trim decisions. When you're done I would just make sure your operators have knowledge of how to trim the speeds. Your electricians may need to train them. This statement is what scared me the most: Edited 24 Aug 2006 by GerryM

[ssommers 20]

I wish this mill had a transmission! All our 7 other mills use 1 motor & a backshaft transmission for the sizing section. This one was an "experiment" about 13 years ago and that person left the company shortly thereafter. I think I'm the only person who's come along since then that has any drives design experience and I have just enough to be dangerous. Currently, the operators put a tach on top of the roll and then changes the gain parameter up or down depending if they need it faster or slower. It can be trial & error for inexperienced operators and some will just throw their hands up in the air and call an electrician instead. The worst part is that each gain change affects all the downstream drives. So a roll change at position 2 means checking rolls 3-8 as well. With the new setup, they'll actually have to tach the fastest roll first under no-load conditions - roll 8 or the last roll used - and then set the rest of the speeds going backwards. It will probably take a few laminated posters, but I think the operators will be able to adjust. How do you have your master & trim pots setup? Just trying to see if there's a better mousetrap before I set this one... Thanks, Susan

[GerryM 2]

I don't know for sure. I'm the only one in the office this week. One of our other guys, who knows in detail, left the company last quarter. He left notes, but I don't know where they are without digging for a while. Our problems were related to consistent and round diameter. We found that the tooling design wasn't the best and the project took off from that point of view. Along the way it was discovered the trims weren't correct because there should be a small tension between stands and we had the opposite in some cases. My involvement was to replace ampmeters with ones that had an appropriate scale & resolution, add diameter measurement, add a display for the operators, and collect data on all that to a database.

[ssommers 20]

I finally got to install the Master Controller & trim pots on Friday. The Mechanical Engineer finally physically saw exactly what was going on with the drives starting up and we convinced the Plant Manager that it needed to be done. I knew it theoretically, but couldn't prove it until several other mechanical issues were cleared up. Now I have 8 motors with their associated drives that all start up at the same time. The gains are all set at 1 and there are no more dependancies between drives. The final piece came about 6pm. After setting all the speeds the same, I did an unloaded speed test to see if everything came on together. Motor 4 still turned back about 10 degees before going forward. This problem had been noted for about 2 days, so the tool makers checked out the gear box while the electricians wired in the speed pots. The gear box was good. At that point, I had to guess whether it was the drive or the motor. The drive would take less time to change, so I went with that. The electrician replaced the drive & everything started up together as one. It's now Monday afternoon and I'm happy to report that the tube mill has been up & down several times with no problems attributed to the drives. However, I'm curious... What would make a drive send an AC motor back like that? There's no reverse command given to these drives. No parameters or wiring changes were made during the drive replacement. Anyone else ever have a VFD go bad like this? Thanks for all the help! Susan