Logic Analyzer

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. My intent is to capture failure data when it occurs (2-3:00 am, typically) and have it waiting for me rather than babysit the machine with an oscope (my 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. Now that I'm working with machinery cycles of 2-3 seconds, the best resolution I require is 1 millisecond.

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.

If you are using RSLogix5, you might try a Histogram Log

Mickey

Mickey,

Thanks for the suggestion. I had already considered that, but some of the signals involved do not connect with the PLC I/O and short of wiring/programming spare inputs to the PLC, the histogram would not be able to access the external signals. If I am wrong about this, please let me know.

Logic analyser

Hi
I know its not a pc based analyser but for general use have you considered the Budgie Fault Tracker Electrical System Analyser and Recorder.
I havent tried it myself but do intend to. The spec looks great perhaps someone else out there has more info?
They are sold by RS components for £785 Stock code 459-3708 at least they are in the uk.
I have also seen them on the web so a quick search should find a site.

Hi grover1,

Why not consider one of those matchbox PLC with 8 or 16 inputs and built-in clock? Usually 5 or 6 of the first inputs (assuming you only consider the lowest prices) are available for interrupts and useful for the fastest/shortest informations or transients. The limit for timestamping should be between 10 and 25µs. At least with interrupts you could be sure of the order in sequences in case of avalanche.

Use the elapsed value of a 100khz pulse generator as a time base. On double-word counters this gives you up to 12 hours with a 10µs resolution. Add other words for additionnal RTC values : no limit since the elapsed value acts as a ring counter !

Due to very low consumptions in small PLCs (15mA or less at 24VDC without input), use a battery as a power supply and trace power losses in your system. Some products are available for 12V but perhaps more expensive.

Otherwise with any small PLC you'll choose, build a word counting ms or less since the last second or the first scan (see above), make each input writing "RTC+elapsed value+input number" in a stack on its rising/falling edge and that's it. Read the data and rebuild the trace graphically in Excel as needed... which is finally a PC based analyser.

Regards.

Laurent

Mickey Mills

You might take a look at http://www.dataq.com

Could you use something like this.

They have other stuff on their website as well.

I hadn't considered using another PLC to solve my problem. Your idea intrigues me Laurent, because it force me to learn new ways to program PLCs, of which I am fairly new to. Just yesterday a new monitoring requirement came my way and a dedicated PLC may very well be the most cost-effective and least disruptive solution. With my current lack of expertise and time limitations, I need to take an off-the-shelf turn-key approach. Your suggestion isn't wasted and many thanks for your time.

Mickey,

The DATAQ (DAY-tak) DI-730 looks ideal for my application. What I really like about it is the voltage range it offers- I shouldn't have to precondition my signals. I'm waiting for pricing and availability. Many thanks for finding this. I'll post a follow-up if this works for me.