encoder pulses delay

I am tracking a product in a conveyor, I use a photoswitch to start a counter and then after certain amount of encoder pulses (delay) I trigger a ligth but I have to adjust the delay if I increase the speed of the conveyor, what can I do to not have to adjust the delay at different speed.

thanks

Automatically adjust the delay based on the conveyor belt speed?

Raflex,

Just for clarity. You are using an encoder or pulsing device/ system, correct?

Are you using a high speed counter?

You mentioned "changing a delay", can you define how your "delay" and a counter (presuming your counter is counting conveyor pulses) work together.

Perhaps the actuator operates slowly and is too slow at the faster conveyor speed. If this is true please indicate so.

Are you seeking general knowledge or are you seeking platform specific advice?

I am using an incremental encoder 600 ppr, compaqlogix plc and hsc.
lets say that the delay to strobe a light in ppr is 100 from sensor to position (distance in inches) at low speed, if I increase the conveyor speed I have to decrement the delay in ppr so the light strobe fires at the same position.

Not knowing the application I'm just making a guess. If the encoder is connected to the conveyor mechanically then it is already measuring distance not time so it will trigger the strobe at the same position regardless of the speed. If there is a relatively long delay between when the strobe is triggered until when it actually fires, I could see the count possibly might need to be varied. You could probably use scaling and subtraction math program code to provide the proper amount of change. You might also require a higher resolution encoder if one pulse + or - affects the triggering position beyond what you can tolerate.

Raflex, I think what you might be observing is that the PLC does not turn it's outputs on immediately, and the inevitable delays between writing the strobe pulse into the tag database, and it being transferred to the output card become more significant at the higher speeds.

If you are doing all of your code in the cyclic task, there will be a variable delay due to the scan cycle, and there will be a variable delay due to the RPI update time of the tag being transferred to the output module.

You should be trying to reduce this inherant delay as much as possible in your application.

Consider using a either a fast Periodic Task, or, better still, an Event Task, to detect the counting input, and at counter .DN fire your strobe output tag.

EDIT: Event Task triggering from the HSC is not available in CompactLogix, therefore you will have to use a fast Periodic Task. You will have to determine how fast this needs to be.

Then program an IOT to the output mudule if the counter .dn bit is on. This will send the output data to the output module immediately.

Daba, you are right, what I am seeing in our application is what you describe, I just found the task, programs and routines programming manual literature from rockwell. I am going get more in depth with this isue, I am new using rslogix 5000.
If you have a sample code of the possible solution, will be very helpful.

Thanks a lot Daba.

I have not used the HSC module, but on reading the user manual for it, it has four outputs that can be configured to come on at a preset count. Perhaps you could implement your strobe control directly from the module, not from the CompactLogix controller??

Couple that with configuration of the counter to reset on the rising edge of the photoswitch, and I believe the HSC will do everything that is needed in this application.

Someone else who has used the HSC will be able to advise better.

You can use one of the higher RANGES (12-15), and, with a RANGE, you can change the preset, on the fly. The normal count process does not allow this.
SO, determine the functional relationship between base speed and 'where you want the counter to preset', and use a RANGE function. It worked for me.

I reduced the RPI to 1ms and now is significally better, but I still see some variation. I will try to use preset ranges on the HSC.
RPI + scan time is going to affect this delay anyway I think.
Thanks to all you guys.

Raflex said:

..... I will try to use preset ranges on the HSC....

Click to expand...

Yes, I believe that is your best bet, get the Controller Scan-Time and I/O updates out of the equation and you should be good to go.

Once configured correctly, I believe the HSC can be left alone, and do its job autonomously.