Allen Bradley -HSCE/encoder grief

lalion

Member
Join Date
Jul 2003
Location
Ballarat, VIC, AUST
Posts
36
Hi all,
just wandering if anyone else has had problems with Encoders/High-Speed-Counter-Cards in SLC500's. Im trying to integrate one into a rollformer at present but getting grief. The encoder(2000 pulses per rev)/HSCE-card is being used to measure distance between shear cuts.

There are 2 problem areas I find, first the length is not consistantly accurate enough, bouncing around within 7mm in 2m lengths but inaccuracies of 20-30mm at 6m lengths. I initially felt this was due to the physical movement of product not being constant; But reverting the system back to a physical cut trigger greatly incresed accuracy. After a collegue mentioned that Allen Bradley seems to have problems with high speed counts/instructions, Im thinking the cause may be somewhere in the sending of the count from the High Speed Count card to the processor and/or its manipulation within.

The 2nd problem is that for longer lengths (6m) the encoder/counter-card resets, thus the new count is added to the max value (30000) and compared against the required length. The problem is that occasionaly the piece will be cut short (5.03m), when measured this length always corresponds close to 30,000 counts, thus ive concluded that the reset/rollover of the count is somehow causing the problem. Ive tried everything, including puting timers and count restrictions so that the 30000 wont be addded to the encoder count until well after the count has been reset to 0 and is well on (>200), but still the problem. Currently I have placed (but havnt full trialed) a soft reset to take effect before the auto/rollover; but don't hold much faith.

So if anyone has any suggestions or knows of certain bugs problems within Allen Bradley regarding this, it would be great. thanks.
 
I you're using the HSCE, the problem is the update time of the acc count from the hcse to the processor (as high as 35 Msec). Use the hard outputs to trigger the cut--it's much faster (5 Usec). Look in the back of the manual to verify these facts.
Don't try to examine the acc count in your program and act on it--the number is not updated in a timely fashion. Come up with a scheme that utilizes the hard outputs on the front of the hsce--even if they feed a PLC input and you write code using the input, it's a lot faster than 35 Msec.

If you're using the HSCE2, the acc updates are much faster but the hard outputs are a little slower.
 
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