PWM integration with PLC

I currently have an application where I need to integrate 7 Balluff position transducers with a PLC . This is an application which will be used to set the height of seven saw blades. The position transducers which we are planning on using have a PWM output. After visiting the AB site, I found the 1746QS module for the SLC 500. When I got a price quote from my AB distributor, I was a little shocked.
I was curious to know if anyone has worked on a similar application, and maybe has gone about this a different way? Is there a more inexpensive way to interface these transducers with the PLC? I have been told that I need the PWM to get the required accuracy. The length of travel is only about 12 inches. Any feedback will be greatly appreciated.

For something like that we usually use the Balluf that has a 4-20mA signal. If this is in a hydraulic cylinder with standard flow control valves (not servo) then the resolution should be more than enough. You should be getting around 12bit resolution (4096 steps or .003" per count).

By the way the 8 analog input module is made by someone (Spectrum, I think) other than A-B and it has some nice scaling functions available on it that are not available on the 4 analog in that is made by A-B.

It all depends on what you are trying to do with it.

Darren

I think Balluf offers fieldbus interfaces on their transducers. You might go that way if resolution is an issue, although update rate might be a problem then.

Keith

Exactly what are you trying to do?

The 1746-QS does a lot more than just get position feedback from Balluff rods. If you need closed loop control the 1746-QS is a good way to go. Otherwise you will eat up the difference in cost with your time when you are trying to recreate the wheel. The QSCfg.exe has graphing capability that makes it easier to tune your positioning loops and the QS will also allow you to synchronize axes. The dianostic tools are worth the difference in cost.

Do not get field bus feedback rods if you are positioning the saws. PWM is the way to go on the 1746-QS. Other modules like the 1756-HYD02 can use PWM or start stop. The 1756-M02AS uses SSI that can provider resolutiuons down to 1 micron.

I move a lot of logs, lumber, chipper heads and saws. A whole lot.

Qs

The 1746 QS also has 4 axis. The software tool is good to work with. It will require a lot of programing you may not wish to do. I would recomend you look at an independent controler like a Delta Controler. Peter can fill you in on the details. If you dont need 4 axis then you wont need the QS module. I believe the software for both the QS and the Delta controler are developed by the same company. We use the QS on a "slew and skew" infeed to chipping heads. If you have the cash, its a good system. Have a good weekend!

After reading this again I would be inclined to agree with Peter and Bruce. I initially assumed that you just needed to know the position of these things for information purposes. If you are actually controlling them you will want to stay away from the fieldbus options and go with the interface options into a dedicated position controller.

Keith