Speed Sensing

[Big John T]

Kinda hit me that the previous code would fail if one stayed on...

So this one should work...

Edit: This one would replace 16 lines of code and 8 timers the way I did it before...

Thanks
John

 

[geniusintraining]

The link does not work. What is the model number of the part you use?

Thanks
John

Try this one, mine are intrinsically safe but they have seveval to choose from that are not, but they work very well and you only look at the one input and have the prox SW wired to the detector, it also has a speed pot so you can choose different speed of failures

Rotational speed controller

WE 77/Ex-DW

http://www.pepperl-fuchs.com/selector/gui/show_product_detail.kly?selected_prod_id=16072

 

[rsdoran]

Peter, do not think the OSF is avaialable except for Micrologix 1200 and 1500, he appears to be using a 5/0?

 

[rsdoran]

Kinda hit me that the previous code would fail if one stayed on...

Edit: This one would replace 16 lines of code and 8 timers the way I did it before...

Thanks
John

Think you will still have to use 4 timers unless there cutting "time" is very very close, probably be safer using 4 timers. I am assuming you have 4 physical drivers.

 

[TConnolly]

It doesen't happen often but it does happen. Perhaps something with a wide hysteresis zone that once on has to move quite far to be off again...

Hysteresis is exactly the reason I'm questioning the likelyhood of the prox oscillating on/off if it stops with the prox on the edge of the target. If its a problem, try backing the prox away from the trarget slightly so that hysteresis becomes a bigger factor.

 

[Big John T]

Think you will still have to use 4 timers unless there cutting "time" is very very close, probably be safer using 4 timers. I am assuming you have 4 physical drivers.

I'm not sure why I would need 4 timers. I'm not sure what you mean by "cutting time"? As long as any tool is still turning the screws in we keep the air going to all tools until they all quit turning. Most machines have 4 or less air drivers on them some have up to 8... Their is only one air valve for all tools... so only one output is controlled.

DC drivers are so much easier LOL...

Thanks
John

 

[rsdoran]

I'm not sure why I would need 4 timers. I'm not sure what you mean by "cutting time"? As long as any tool is still turning the screws in we keep the air going to all tools until they all quit turning. Most machines have 4 or less air drivers on them some have up to 8... Their is only one air valve for all tools... so only one output is controlled.

DC drivers are so much easier LOL...

Thanks
John

I thought there may be an issue of the "tool" being broken or something if it kept trying to rotate. I was "assuming" each tool was driven separately.

 

[Jimmie_Ohio]

Looking at rsdoran's post #6 and it is wonderful by the way. I came up with this rendition that would knock out a lot of code for a machine with 4 heads... Any reason why this would not work? I don't have a machine to try it on at the moment... I should have one powered up in the next day or two to try it out...

Thanks
John

I would make SEPARATE rungs with SEPARATE one-shots for the individual prox switches, then parallel them into the reset. Or, with RS Logix 500, you could make each of these resets a separate RES rung.

Dang, I'm slow. John, your earlier post is what I was talking about...

 

[TConnolly]

If you have only one output then maybe using a single TOF might be the way to go after all. Would I be correct in stating that each driver has a target and prox? If so then program each one to single shots and have the single shot bits in parallel to the TOF. Once 1/4 second goes by in which none of the single shots has pulsed then the TOF times out, clearning the DN bit. This logic will work no matter how many drivers you have, be it 4 or 8, or more.

 

[Big John T]

I thought there may be an issue of the "tool" being broken or something if it kept trying to rotate. I was "assuming" each tool was driven separately.

These air tools are screwing bolts into small engines... If one keeps rotating for what ever reason (missing bolt etc) the auto time out kicks in after usually 8 to 10 seconds and faults out and makes a loud noise (you don't want to be standing next to the speaker) and breaks the auto cycle.

John

 

[Big John T]

If you have only one output then maybe using a single TOF might be the way to go after all. Would I be correct in stating that each driver has a target and prox? If so then program each one to single shots and have the single shot bits in parallel to the TOF. Once 1/4 second goes by in which none of the single shots has pulsed then the TOF times out, clearning the DN bit. This logic will work no matter how many drivers you have, be it 4 or 8, or more.

Yes, each driver has it's own prox and target and input into the plc.

I tested my last code on a PLC and it seems to work no matter what state any input is in...

Thanks
John

 

[Big John T]

Peter, do not think the OSF is avaialable except for Micrologix 1200 and 1500, he appears to be using a 5/0?

Most machines have 5/03's or 4's with some compact logix and a few scattered 1200's and 1500's for good measure...

John

 

[Kabir]

I did not have time to read all the replies you got.
I would just offer a small suggestion.

Some time ago I installed a small plate with a couple of holes in on to a shaft. A proxy was fitted to sense the holes on the plate.

I used a counter and a timer which each one of them Done Bit trigger a CPT instruction that used the accumulator of both to calculate the RPM of the machine and store it as a float. This way you could display the RPM on an HMI as well as you could set High and Low Speed Set point and plot the speed vs. time graph of the shaft.

Look at PLC scan time as well as input card response when checking higher speed shafts

 

[wildswing]

John,

We use similar setups to detect motion faults. Here's an example of the logic we use...

The mirror (or dummy) bit allows us to use one timer. The timer resets on the ON > OFF and OFF > ON transition of the prox input. Preceding this with the MOTOR RUNNING feedback stops false alarms when the motor is stopped.