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Hi all,

I'm new to this forum and wish to pick the brains of anyone that could suggest a fix  for a very unusual problem is occurring on a vision 570 with v200-18-E3XB snap in.

We have built 5 identical machines that are essentially batch fillers using the vision 570 with V200-18-E3XB.  All machines have identical programs.

We have a flow meter that pulses out 1 pulse for every gram of product or about 25 pulses per second. we feed this pulse into the HSC and totalise until the desire value is reached . simple! except one of the machines counts for a while , say a minute  or two, then the  plc decides to stop counting. the counting doesn't just stop , it ramps down to zero  over a period of say 5 seconds. 

when this first occurred I check the wiring from the flow meter to the  plc with a digital counting multi meter and all  was good .  It was then I noticed one of the connector block on the digital inputs wasn't all the way in . about 2 mm out . I pushed it in and the problem disappeared. problem solved I thought! but the the problem has come back and the connector blocks are all seating well. 

has anyone come across bad soldering on connections of input terminals on this product or know what else it could be ? 

 

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Swap the PLC and the IO module from one machine to another.  If the problem goes away it's in the PLC hardware.

If it doesn't go away, there's a problem in the pulse output of the flow meter.  Do you have an oscilloscope or a meter that can read frequency?

Joe T.

 

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hi Joe,

I wish I could but the other machines are in operation and in a different state! (location) . I plan on on getting the faulty machine back here for further analysis. 

I don't have a oscilloscope but do have a DMM with frequency input . I already used this the check the frequency output of the flowmeter all the way back to plc and it was fine . saying that I dont know what the trigger voltage and time scale  is for the DMM vs the PLC. I might invest in oscilloscope to better understand what if if any changes are happening to the signal. 

while I am the designer of the overall machine, I did not program the PLC . this was outsourced. the programmer is very knowledgeable with lots of different brands and has several years experience programming PLC's . His core job. 

  I do not pretend to fully understand the ladder logic but  something else  bugs me (and the programmer)   about the code or plc when it comes to the HSC on the vision.  let me elaborate ...

we are using an emerson micro motion  1700 transmitter to send a frequency output to the PLC. scaling output method is set to "pulses per gram". In the cal settings of the plc HMI there is a user definable input for this relationship . i.e we set the 1700 flow transmitter to 1 pulse per gram and the PLC set to 1 pulse per gram and all good! except it doesn't work . we have had to set the flow meter to 2 pulses per gram  and the plc to 1 pulse per gram to measure correctly !! while trying to fault find what was going on I used the flowmeters diagnotics tools to fix an output frequency of say 100hz. when the plc is set to 1 ppg I get a reading of 50 grams per sec on the plc. when I set the plc to 2 ppg I get 17-20grams per sec on the plc instead of an expected 25!

As the set value of pulses per gram is raised the error gets worse.  And I notice the value wanders up and down a bit !! 

Note : This error occurs on all the machines. something not good is HSC land?

happy to forward the program if you want a look . 

 

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Do you have / can you borrow another EX3B module to try?

This is why I carry a USB scope in my car.  If the pulse output of the flowmeter is really short, too low in amplitude,  or wanky shaped the PLC may not recognize it.

This is my unpaid endorsement (assuming you're in the US)

http://www.analogarts.com/products/usb-oscilloscope/sa915-100-mhz-bandwidth-oscilloscope

It's very capable for $200.  I personally have the 500 MHz model and a couple of Chinese 250 MHz probes, which works well on both industrial machinery noise-finding adventures and troubleshooting antique radios from the '30's. 

I found several even cheaper on Amazon.  Depending on how many hours you've spent trying to solve this problem, it may be well worth it.

Joe T.

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