25 Year Old VS Drive System Integration Help 2

[beauxdog]

We are in the early stages of replacing a 25 year old engineered V/S drive system. The plans are to have the new system completely engineered and installed by November of this year. In the mean time we want to start the integration of the existing drive system into our DCS system. This step starts with automatic draw control of various drive sections. Easy enough to measure the draw and input it into the DCS, hard part getting the drives to accept a signal from the DCS (Honeywell TDC3000, only knows 4-20mA).

The drive system has a master pot that determines overall line speed. This voltage is then sent to each on the drives on the machine. At each drive there is another pot that is used to bias speed off of the master speed i.e. draw control. As in most drive systems of this vintage the pot is used as a voltage divider to supply a reference to the drive. In this case the master line speed is a 0-8VDC signal that signal is then sent through a pot to common and the wiper provides the speed reference in a range of 0-4VDC.

There are many manufactures of signal isolators and converters that will change to 4-20mA to a voltage signal Moore Industries, Action Instruments, etc. These will not work in this situation because the need to used the master voltage and divide it to get the speed reference.

My question does anyone know of anyone that makes a device to pull off such a task?

Thanks for any help…!

 

[rbulsara]

Not an expert in electronics or transducers, but search for dc V to 4-20mA tranducers. I know AC V to 4-20mA tranducers are available.

Failing that, how about using a fixed resistor wired as load to the voltage signal to produce mA in series with 4-20mA device? I would think the V source would have the capability to deliver some power (milliwatts).

In fact a transducer can't get any simpler than a resistor.

R=V/I

 

[rbulsara]

You need to take the internal resitance of source into account, which can simply be calculated using a known load R and simple measurements.

 

[beauxdog]

The power supplies must be isolated, DCS and V/S drive. The device I am looking for is kind of like a ‘4-20mA to 5K ohm pot’.

Thanks for your replies

 

[Laplacian]

If you're interested, our local supplier for such instrumentation has probably seen it all. He supports large refining/chemical plants in the area that have a variety of old+new instrumentation intermingled together.

Let me know if you would like the contact information.

 

[beauxdog]

Laplacian, thanks for the post. I would like any contact information you are willing to provide.

Again Thanks,
beauxdog

 

[DickDV]

Guess I'm missing something here. Why not let the signal isolator provide the 0-8vdc master signal and retain the individual section draw pots to divide down to 0-4vdc.

Most isolators will accept the negative side of the voltage output being a common (even ground) which would mimic the present system, it seems.

What am I not seeing, beauxdog?

 

[beauxdog]

The isolator must truly be isolated. The idea is to provide draw control in each section of the machine. The master speed is generated from a single pot, then each drive must vary from that signal based on current draw requirements. I do not know how to explain that it is imperative that both systems, DCS/VS drive must be isolated. The most basic explanation is that I need a 4-20mA to 5K ohm isolator.

 

[jraef]

Are you planning on an AC drive system or DC? If it is AC, many new drives now come with that as a built in feature. You can set one as a master, have the others follow it as slaves and give each slave drive a trim pot to adjust the ratio from the master speed. There may be some DC drives that offer that now too, I just don't use them so I am not familiar.

"Venditori de oleum-vipera non vigere excordis populi"

 

[rbulsara]

Check this out. Contact them, they may be able to make up something for you.

http://www.elkor.net/etvi.htm

 

[ScottyUK]

Thinking about this, the wiper of the 5k pot must be connected to some piece of circuitry further in to the contro system. If the pot is just providing a variable DC input to a high impedance input on the controller this should be quite easy to replicate electronically.

If you need an attenuated replica of the master signal - is this correct? - then why not create some additonal DCS points and use the DCS to provide the requisite scaling through software to drive additional 4-20mA outputs, one with 100% span and the others with reduced spans that your operator or engineer can adjust to suit the process?



----------------------------------

If we learn from our mistakes,
I'm getting a great education!

 

[jonpayton]

Wow must be a Reliance Max Pak VS drive. Great old drive we still have some in service where I work. It takes a zero to 10 volt run reference. I beleave Reliance still sells a card like you described. Some of the best were made by a company called ESI out of chattanooga TN. They are no longer in business. I beleave one of the engineers still works in Chattanooga for another company I'll try to find a web page for him.
You typically have one motor called the lead motor. A pot will supply a board called a LMR (Linear master reference). This board will adjust the ramp reference for the system, speed of shutdown etc. The signal would then go to 4Ia cards. Real simple cards just op-amps really. They have pots for adjusting each drives speed. You could build your own. You'll also need something to automaticly adjust the speed of each motor slightly. For instance in a web application dancer rollers to keep everything running together. I could probaly get you drawings of a complete machine boards etc. I also have drawings of every Reliance drive ever built. I think! I have working on systems like this for about 30 years. You can do it many different ways PLC's etc, For your drives you may be on the right track for the simplest system. I'll see if I can get a web sight for you and post it.

 

[beauxdog]

Thanks for the reply. Any information that you have would be greatly appreciated. Thanks again beauxdog

 

[DRWeig]

Hey Beauxdog,

Full disclosure: this is a product my company makes, analog-to-resistance transducer.

http://www.kele.com/olcat/ot8/RES-1.PDF

Special ranges happen all the time too.

Holler at me if you need any additional data.

DWeigel@kele.com

 

[cbarn24050]

Hi, this is not so hard to do, all you need is an opto isolator (linear type) a suitable op amp (TLC2201) a few resistors and 2 pots (gain and offset adjustment). It should be able to self power from the drives "pot" terminals.

 

[beauxdog]

DRWeig thanks for the reply. Thanks everyone for their replies! The link in the post does not work on my PC. Do you have a model number?

 

[DRWeig]

BeauxDog,

RES-1-S is "special range" version, you specify the minimum and maximum ohms output. It can be up to 1 megohm, minimum span 30 ohms. You can find it in the "output transducers" section of

http://www.kele.com

under Kele catalog.

Best to ya,

Old Dave

 

[jonpayton]

Subject: pricing


John,
Here is the pricing for most of the boards we build. They are the same as
the ESI boards except we added some features that weren't on ESI's. Balus is
our technician who builds these and he did all of them for ESI for 25 years
before coming here.
Pricing:
PPD-4-320 $605.00
4IA $430.00
LMR3 $410.00
ACC-FR $605.00
PS-1 $ 52.00
PLC1 $1150.00
PWR $358.00
Mt. Vernon has terms of 1% 10 days on the purchase orders to us. I will get
back with you on a meeting for next week as soon as I can get a date Balus
and I can both make it. Thanks Charlie Johnson 1-423-629-4014 FAX
1-423-629-4177

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1/28/05