Best Way? Line Speed (Encoder)

[rootboy]

I have it working, but it does only a peak and it holds it... The value never goes down, but only up... and it stays up at a peak and never falls...

Thanks,

John

Can you take a screen shot with some live data in it for me? That would help.

I have my original average program back home, and I wrote (or mis-wrote, apparently) this from memory.


Thanks!

 

[JohnnyQuanex]

Yes, I will try to get that Monday...

Thanks for all the help...

 

[JohnnyQuanex]

Can you take a screen shot with some live data in it for me? That would help.

I have my original average program back home, and I wrote (or mis-wrote, apparently) this from memory.


Thanks!

Here's the logic... I added a truncate instruction to clean it up... Like I said, the value just increases and holds; it never falls... (It also takes a long time to stabilize; not much better than the my other time/average setup that I started with...)

I've also included another rung of logic (second picture); this is where I'm trying to use the line speed value as a control feature to error-proof my encoder (in case the wheel loses traction with the product...). I'll probably develop some alarm features with that too, but for now I just need a fast, real-time value for this logic...

I read a couple of posts that said I could change my encoder to velocity, but I'm not sure what that would do to my current counter logic... I'm open to learning more though...

Thanks,

John

 

[JohnnyQuanex]

There are two varieties of 842 series EtherNet/IP encoders.

The ordinary 842E-S and 842E-M are single-turn and multi-turn absolute encoders that are treated like I/O modules with a cyclic connection.

The 842E-CM-S and 842E-CM-M are CIP Motion versions, which are actually an axis in the CIP Motion subsystem of ControlLogix and CompactLogix controllers.

On the non-motion modules, look at the Module Definition on the General Properties tab in Studio 5000 for that encoder. You'll have to click the [Change] button (in offline mode) to modify the Input Data type.

The default is Position, but you also have the option of Position + Status or Position + Velocity.

The speed will then be calculated onboard, with the units you specify in the configuration.

Edit: Ian beat me to it by 20 minutes !

Ken, Ian,

I setup my program with the velocity setting as a trial...

What now?

How do I use that to program a counter and how does this help me with line speed? (Special instructions?)

Thanks,

John

 

[JohnnyQuanex]

Here's the logic... I added a truncate instruction to clean it up... Like I said, the value just increases and holds; it never falls... (It also takes a long time to stabilize; not much better than the my other time/average setup that I started with...)

I've also included another rung of logic (second picture); this is where I'm trying to use the line speed value as a control feature to error-proof my encoder (in case the wheel loses traction with the product...). I'll probably develop some alarm features with that too, but for now I just need a fast, real-time value for this logic...

I read a couple of posts that said I could change my encoder to velocity, but I'm not sure what that would do to my current counter logic... I'm open to learning more though...

Thanks,

John

Okay, I think I improved the stabilization time problem by reconfiguring the multipliers in the CPT instruction... I changed the around so that the feet per sec would be the leading object...

Looking at it again, I think it also solved the peak and hold problem...

I'll verify, but it sure appears like it has...

Thanks,

John

 

[JohnnyQuanex]

Okay, I think I improved the stabilization time problem by reconfiguring the multipliers in the CPT instruction... I changed the around so that the feet per sec would be the leading object...

Looking at it again, I think it also solved the peak and hold problem...

I'll verify, but it sure appears like it has...

Thanks,

John

Okay, so it is working pretty well now. I do have a problem though; the feet per minute value is spiking from 120 to 178 fpm every few seconds... I think it's occurring when my feet per second value goes from 2 fps to 3 fps and back...

What can I do to stabilize that further without slowing thing down?

BTW: The minimum speed value, I changed it from 10 to 1 because our products only run 2 - 5 fps depending on the product...

Thanks,

John

 

[JohnnyQuanex]

Okay, so it is working pretty well now. I do have a problem though; the feet per minute value is spiking from 120 to 178 fpm every few seconds... I think it's occurring when my feet per second value goes from 2 fps to 3 fps and back...

What can I do to stabilize that further without slowing thing down?

BTW: The minimum speed value, I changed it from 10 to 1 because our products only run 2 - 5 fps depending on the product...

Thanks,

John

Okay, I was wrong. The values stays up when the encoder stops...

Here's a new snip of our line stopped...

It needs someway of resetting the running average maybe? A reset would be too discrete though. I need real-time data so I can detect subtle speed changes and use that data to for control features...
Thanks,

John

 

[AustralIan]

Use REAL values rather than DINTs.

 

[JohnnyQuanex]

Use REAL values rather than DINTs.

Ooooh, okay...

Let me try that...

Thanks,

John

 

[JohnnyQuanex]

I think I set everything to use REAL values... (except the timer)

It still does the same thing...

 

[Doug-P]

Would a thread on filtering help?

http://http://www.plctalk.net/qanda/showthread.php?t=43380&highlight=filter

 

[Ken Roach]

Why are you experimenting with ladder logic to calculate the velocity when you have a tag that literally gives you the velocity of the encoder, calculated automatically inside the encoder ?

 

[JohnnyQuanex]

Why are you experimenting with ladder logic to calculate the velocity when you have a tag that literally gives you the velocity of the encoder, calculated automatically inside the encoder ?

Ken,

I wrote this earlier today...

_______________

Ken, Ian,

I setup my program with the velocity setting as a trial...

What now?

How do I use that to program a counter and how does this help me with line speed? (Special instructions?)

Thanks,

John

 

[JohnnyQuanex]

Ken,

I wrote this earlier today...

_______________

Ken, Ian,

I setup my program with the velocity setting as a trial...

What now?

How do I use that to program a counter and how does this help me with line speed? (Special instructions?)

Thanks,

John

Ken,

How do I count with the velocity tag?

 

[JohnnyQuanex]

Ken,

I downloaded the program with the encoder setup as a status-velocity... Is there a way to have velocity and position status so I can use the encoder for both..? I don't see any obvious way...

I can't see how to count feet with the velocity settings unless I would simply multiply the rpm by the circumference of my encoder wheel... That doesn't seem like the best way to count...

Any advice would be appreciated...

Thanks,

John