842E-M Ethernet IP encoder

[IamNotaCat 0]

Good Morning,

I am considering during an upgrade attempting to use a 842E-M Ethernet IP encoder. I see I can configure it to read both position and velocity. For my application, I want to know total product ran and current line speed. The velocity seems pretty straight forward. If I have a 12" tracking wheel, and I set it to Rev/Min, then I essentially should have a direct Feet Per Minute (FPM) readout from the Encoder.I.Velocity tag (I hope). The counter part is what I am having trouble understanding how to configure from the manual. (Unfortunately I need to make sure this will work before I can buy one, so I can't bench test). 

So say I set Resolution to 10,000 counts per revolution, and revolutions' at 1  (Maybe even could swap to 842E-S now that I think of it). My position should count up 10,000 times per 1 revolution, and that would tell me I've ran 1 foot. On my old SLC 5/04 with a 1746-HSCE2 card, I could roll over back to 0 after my count and just count up a counter every time. I can't find any sort of 'Roll over' or definitive information in the manual about this. It seems most application examples in the manual are expecting back and forth applications of some sort. Of course, I could just do a modulus command or something like that to keep track, but then what happens when the max position value is entered? The max value of the position counter register at 10,000 counts would hit overflow by 6100 feet ran. 

 

I am clearly missing something, has anyone done a similar application before? 

[Joe E. 259]

How much resolution do you need? I've used a resolver with a 1' circumference wheel before in a very similar application. We only needed the total accumulator to be accurate to within 1'. We configured the resolver to (I think) 1024 counts/rev and incremented the count any time the position was within a certain range (0-10 or something). You could set up more windows to get more resolution. BTW, this machine was running at about 45'/min, so it wasn't high speed. If your system is much faster, this way may or may not work.

[IamNotaCat 0]

Max Speed is about 200 FPM, with a 12" wheel It would mean 3.33 revolutions per second. I just don't understand how the counting goes period on that one. On old HSCE counter on my 1024 PPR pulse tach with a quad encoder, it would count 0-1024 and reset, so I had a GEQ 1000 with a one shot to increment a counter saying it ran 1 foot. Since it resets at 1024 the next run through is always 1024 pulse counts before it gets back to the 1000, kept a pretty accurate count.

 

With this things position value, how does it reset? Am I going to hit overflow or does it automatically zero out at max value... which was 0x3FFFFFF I believe. This means even if I did 1024 counts / rev and maybe modulus the position with 1024 to get a 'Rev' count which would be a footage count, at max I could store around 65,000 before maxing out the value. Would I need to just store that value, trigger a position count reset, start counting again, and do a summation?

[IamNotaCat 0]

As of right now what I was thinking is I may have to use the CIP message to set up endless shaft functionality.

 

[Joe E. 259]

In my experience, when a single-turn encoder "rolls over", it just goes back to 0. So you could do exactly what you mentioned with a GEQ 1000 and a one-shot. That's what we did with the resolver I mentioned above. I would expect that to work fine for what you're doing. Your pulse may be a little "late" sometimes, but as long as you don't miss any windows, it will total out to be accurate within a revolution.