Internet PLC Forum

If we setup a HSC using the HSCDEF statement and then the counter trips the function associated with it in the HSCDEF statement.  Then through some sort of movement in an encoder it decrements the counter and then increments back to the set point that trips the function again and again and again.  If this occurs at such a rate could a recursive type action occur in the calling of the function associated with the HSCDEF statement?  For example:

HSCDEF 1,1,1000
//  when the counter hits 1000 it trips function 1
//  the counter dithers around a difference of one count down
// and up and fires function 1 again before the first function
// finishes, what would keep this from happening over and over // at high speed, thus causing a recursion of some sort?

Function 1:

OUTPUT[1]=0
REFRESH


P.S.  Does the refresh statement take precedence in execution over the updating of the HSC?  Thus a missing of counts while the refresh occurs?


Thanks again, great product and may the new year bring even more success to your company.




 

Hello again,  after about five years of use of the MD888 in my facility, its still going strong.  The only problem I have with the unit is the HSC is not keeping a consistent count.  I gain/lose pulses all the time.  I have commented on this problem in the past here in this forum, trying the suggested solutions with no improvement.  

I have the 888 connected to a HMI using the Omron protocol through the RS232.  The HMI displays a scaled value of the HSC that relates to the position of a log relative to a saw blade.  I can set the HSC on the fly after verifying the position with a tape measure.  Ie, the tape reads 12" so I enter 12" on the HMI and scale that input back to the correct HSC value.  By the end of the day this is off by several hundred counts.  My feedback device is a Quadrature Encoder.  I have used several different encoders with no improvement.

I know the knee jerk reaction is electrical noise.  I have eliminated this thought by 1.  O-scope inspection.  2.  Ran a test program that sets the HSC inputs to interrupts and seen if there was any noise tossing the inputs around.  No interrupts were fired.  I am confident that noise isn't an issue.

I did have some limited relief using this  http://www.beiied.com/PDFs2/AntiDither.pdf
which leads me to believe that maybe under certain circumstances the SETSYSTEM 4 command fails.  I am not sure if at certain frequencies the encoder transitions sent to the HSC are not being handled correctly.  
I am not sure if anyone else has had these issues with the unit.  I really like the PLC, they are awesome in my opinion, but I cannot get this problem resolved.  

I am willing to try another solution if all else fails, but to me its quite extreme.  I am considering sending the encoder channels to schmitt trigger RC low pass filter then to a D Flipflop(for each channel) that is clocked with a much lower frequency than 10khz(spec of the PLC), but higher than my max output frequency of 1.3khz; putting the encoder channels on the D inputs and only sending the channels out to the HSC inputs on the clock transitions.   I really don't want to do this.

If it helps anyone, I have used both open collector output encoders and line driver outputs of A/A' B/B' and none of this has helped.  

I will give a better description about all of this, if I see an interest in resolving this problem with everyone here.  All ideas are welcome.


Regards

Hello support,

I have some questions.

1. What happens when the encoder inputs (MD Series) are pulsed faster than 10khz in quadrature mode?  1a.  Does it still count? 1b.  Stop counting. 1c. Get a random count?

2.  On the analog inputs, should we ground the unused inputs?


Thanks in advance and as always thank you for a great product.

I am sure this has been discussed before, but why does the RTC cause my HMI to time out from time to time.  I read in the doc's a bent pin can cause this, but I checked this several times and it continues to do so.  Any help would be appreciated.  

BTW, I have a MD888+ and this didn't happen before it was installed with the RTC.  I need this  in case of power outage.

plc_user