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Guest grover

Logic Analyzer

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Greetings. I need to monitor eight, 0-24VDC signals over a 24-hour period to help solve an intermittent machine failure. Some, but not all of these signals interface with the A-B 5/30 machine PLC, therefore, I don't think an RSLogix histogram log would work. My intent is to capture failure data when it occurs (2-3:00 am, my typical luck) and have it waiting for me rather than babysit the machine with an oscope (my otherwise favorite tool of choice). When I worked in the semiconductor industry, we made frequent use of logic analyzers to monitor the real time logic level of up to 16 digital channels. The resolution of these devices was quite impressive, down to 10 nanoseconds or less. The problem is they cannot scale down to the 1 millisecond resolution levels that I require now. Any ideas on an application that would work on a Windows laptop and cost no more than $1,000 or so? I would appreciate any feedback. Grover

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How about a Paper chart recorder...I had a similar instance on a thermoformer that was hickcupping once in a while...Rented a Hospital type chart recorder...I beleive it was 42 points I was looking at...Ran all night long and it turned out the problem was the contracator's drill...every time he would hit his button to drill his hammer drill on the new area they were installing the noise was picked up on the recorder an you could see the major spikes that influnce the control power on the machine....We installed line filters on the control power and "walla" problem never happened again...

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I've run into the same type of situation several times and an extra plc does the job well. I've got a very expensive 16-input DAQ device but why would I leave that on a jobsite along with the needed computer when a small plc will usually do just as well? Just set the input filter time down to zero or whatever you need (I'm assuming you can do that with a AB plc; can't recall) and program it to record the input #, time, etc whenever any input changes state. I had one tough problem where the plc was able to prove it wasn't electrical but rather a mechanical problem. Because there was just too much data to record for any great length of time, I gave the plc the ablilty to search for data patterns as triggers before writing data to memory. As we narrowed the pattern down we could quickly input our new ideas of what the pattern should be into the plc via an HMI screen we had connected to it. We gradually reduced the amount of recorded data that had to be ploughed through with better and better patterns until we understood what the problem was. Worked really great. I Used a bottom of the line micro plc from Mitsubishi. I would not repeat that experience today; I'd use high end DAQ equipment, record everything in one shot and analyze it offsite but it worked well with our limited resources at the time. Most cases are much easier to diagnose and a quicky program into a spare plc is as good as anything. A side benefit of buying a plc for the job is that you can use the plc in your next project. If you buy special test equipment, you get to admire it on the shelf! Even renting is money down the drain by comparison. Jim Rowell

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How about to add a subroutine which store the status you concern when it is changing. and import all the datas periodly using your labtop. If the resolution is "down to 10 nanoseconds or less" , my suggestion is to devolop a singlechip graping the changing . Good luck.

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