Potentiometer and analog volt out

[darrenj]

man... most of the guys on my maintenance crew regard VFD's as black magic. .

LOL we all know its not Black Magic...Its voodo majic!

 

[Matthias von Zorn]

Thanks for all the replys guys. It is a boston gear RB drive. I cant seem to locate the voltage output on it (ie, 12v, 24v,etc ), but its a 5k ohm, 1/2 watt pot. Anyways, the reason im doing this is cause we have built a new furnace system, and rebuilt an old one for a customer. They have a very facny wonderware system with every bell and whistle on the planet. But, since the old furnace has this dc drive (and it works, dammit (maybe it needs to meet an unfortunate accident)), they will NOT replace it. And, its just burning me up that I cant set conveyor speed on this system, which makes 1/2 of my control and feedback system useless (for the second machine, first one is new and has it all). They wont pay for a new DC drive with a speed referance. So im trying to "make it work" on my budget of 0.

 

[DanielCamacho]

The real world...

Soryy to hear that, unfortunately I have faced simular situations. It makes good sense to upgrage a relatively inexpensive part so that the production can be increased or just to ease the jobs of others, but often the people that hand out the cash don't see it that way... You may be able to submit something tangable (in writing) how this would improve things. Bottom line they want to see a return for the investment... Is there a spare parts wharehouse on site, maybe maintanence could remove a new drive for you... Just an idea... Good luck...

 

[JesperMP]

I cant seem to locate the voltage output on it (ie, 12v, 24v,etc ), but its a 5k ohm, 1/2 watt pot.

It must be possible to find out what voltage it uses. And you need to know it to match it with the analog output.
It is possible that it is an isolated DC input/output so that you cannot measure between the supply out and ground. You should be able to measure between the DC+ and Gnd/DC- terminals on the drive.
If you measure "+5V" on the terminals, and it floats between the terminals and plant ground then it is probably isolated.

If it is isolated, then you need a signal amplifier that:
1. Scales you PLC output 10VDC to the drives 5VDC (5VDC just as an example).
2. Can be driven by the drives supply terminal (on the output side of the amplifier).

 

[Matthias von Zorn]

It just makes no sense. Residnce time, process prediction, maintenance monitoring, etc all need to know how fast the belt is moving. They arent even going to use 1/2 the abilities of the system, all for the cost of a 400 dollar drive. It really is madening. Oh well. Thanks for all the input.

Matt

 

[Steve Etter]

Matt,

I just did a quick Google search and did not find the Boston Gear RB drive. Do you have any additional info on it or maybe a website where I can download a manual?

Steve

 

[Matthias von Zorn]

I have the manual, and it hasnt been much use. The webstie is www.bostongear.com The Doc No for the drive is 19025. They are also called Ratiotrol drives. The fact that the NO4v isnt isolated has me very nervous to do this now as well. I do apprecate all the help tho. I found an isolated SLC card, but of course, theres no budget for that either

 

[rsdoran]

This is the manual: http://www.bostongear.com/pdf/upload/lit/Beta%20Manual%2019025.pdfLooking at the schematic on page 25 it seems to be using a +10v source for the potentiometer. It also uses a control transformer that seems to separate (isolate) the control from the motor output.

As mentioned a signal amplifier/conditioner that can take your analog output and convert it to the drives input values may work.

Another option is the use of a digital potentiometer.

Another option is design your own speed reference system using resistors or multiple pots preset. Example: Use 10 resistors (or pots)with 10 relays to pre-set 10 speeds...ie 1v=10%, 5v=50%. The manual shows using a 5K pot so 500ohms would give 10% of max, etc etc.

The last requires more effort but its a cheap option, I have had to do this a few times.

 

[Lancie1]

Matt,

I will repeat myself. All you need to add is a low-cost signal isolator, also called a signal converter, a DC-to-DC Converter, or a Signal Transmitter.

Put a voltmeter across the wires coming from the existing pot to find what voltage level is needed (0-5, 0-10, and so on). Buy an isolator and add this between your PLC module and the DC Drive. See the link below for an example that WILL work. This one will accept 6 different input voltage ranges, and convert to any of 6 output ranges. If your company won't pay for this needed device, then you have a serious problem that cannot be solved with any type of device. A swift kick to the boss's rear end might be more appropriate...

http://www.kele.com/cgi-bin/navigate.cgi?cat=Model%20DT13&js=setuser

 

[Matthias von Zorn]

Wow, thanks for finding that. I looked at the schematic a bit too, but wasnt able to trace the voltage down. I am definetly armed with enough info now to make this work, one way or another. Thanks again guys. The problem with the budget is this company didnt buy any of these systems for the rebuild. But, since its all there for the first machine, I am trying to give them the extra worth. So I have no budget for it, because it was never puchased. I developed and programmed the whole system, and it eats me up not seeing it run on the second machine, even though it wasnt even suppost to be there. Thanks again.

Matt

 

[Unregistered]

" I looked at the schematic but wasn't able to trace the voltage"

Maybe in your toolbox you have a yellow box with a display , and two cables with needle things on the end - this is called a multimeter -

Give you a clue , this can help .

 

[rsdoran]

I am not sure Matthias is the one that needs to get a clue. There are many situations where using a meter may give you a reading but will not provide the specifics. No load and load voltage can vary significantly. Thats why so many mention matching impedance.

I see a +10v reference, the actual output could be much higher with nothing connected. If a 1/2 watt 5K ohm resistor is connected then measuring across the pot should give you a reliable reading of the drives analog voltage.

I am sure there have been many situations where "budget" issues didnt allow you to obtain exactly what was needed for a situation. In many cases you may have some used or stockroom components that may be used. Thats why I mentioned using relays and resistors, many plants have those in stock. In conjunction with a discrete output card its a cheap reliable method to vary the speed with an older style dc speed controller...I have had to do it on numerous occasions.

Maybe I dont have a problem with it because onct upon a time ALL the machines used things like pots, resistors and relays. In the paper industry if you made envelopes the older automatic die cutters didnt have PLCs, they used potentiometers for positioning, speed etc. They may have a bank of 50+ pots. The last one I dealt with was a F.L. Smithe PHP.

 

[Matthias von Zorn]

Or maybe the actual drive is 1500 miles away, and all I have is a manual to go on? And maybe the schematic RSDORAN posted was a bit tuff to read in my faxed copy of the manual and I missed the volt referance. Geez, you dont think I dont know what a multimeter is?

 

[johnnysparks24]

Dart Controls for Variable DC

Hello,

In a above reply, it was said to connect a voltage analog output to the Common and Wiper terminals.

Common (-) and Wiper (+)

In Dart Controllers the Speed pot is connected to Pot LO (P1)
Pot Wiper (P2)
Pot HI (P3)

according to the schematic P3 is connected to +12vdc which is the internal supply. P2 is the variable that controls the desired speed. P1 would be low or ground.
So I would think that you would connect a 0-10vdc from a analog output card to P2 (+)
P1 (-)

In an earlier post of mine on the same topic someone said to connect the PLC analog output (0-10vdc) to a dart controller via P2 and P3.

Any suggestions.

John

 

[Steve Etter]

In theory, you are correct. The positive from the PLC analog card would tie in where the wiper would normally go.

One word of caution - it appears you are talking about mixing references and currents. This can cause you big problems if the two systems are not designed for this. I would suggest using an isolation board between the PLC and the drive. By doing so, you will reduce the opportunity for burning out your drive or PLC card.

Steve