Oscilloscopes and Logic Analyzers

Recently I've been asked to solve a lot of automation hardware problems that involve very short duration disruptions in power or signal, and it would be great to have a digital storage oscilloscope to diagnose them. Being a member of the sales department, though, such heavy-caliber diagnostic instruments are beyond my budget.

So I've been looking at PC-based instruments like the BitScope.

Does anyone out there on the Forum use a BitScope or similar PC-based oscilloscope or logic analyzer ? The biggest drawback that I'm seeing from reading the specifications is that these devices aren't as well isolated and can't handle the typical voltages we work with; the scopes won't handle 120VAC and the logic analyzers are built for 5VDC, not 24VDC. I'm hoping that others know about converters, probes, or other techniques that I am unfamiliar with.

I've used this one, and some other similar ones, worked pretty well.

For high voltages (heck, even for scopes that can handle them) I still like to use differential probes. You might be able to simply use a 10:1 or 100:1 probe too, if it's not on a floating ground system.

Ken Roach said:

Being a member of the sales department, though, such heavy-caliber diagnostic instruments are beyond my budget.

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Your name came up at my last meeting with my AB distributor and they had quite an interesting story about your position with RA and when you first signed on. If your job description above is accurate they must have been blowing smoke. Too bad too it was a great story. I am still impressed with your contributions here though keep up the good work.

To your question I have not used any of the pc based scopes.

ken.
I bought one of these USB scopes a while back & really like it.
http://www.usb-instruments.com/oscillo_stingray.html
It won't take the 120v signals without the differential probe linked to above. I haven't purchased one yet, so I cant testify as to their performance. But it works on signals below 50v well. I really like the signal/wave generator part.

Measuring High Voltages

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The DS1M12 is rated at +/- 50V DC maximum input ( 35V RMS AC ) even with a x10 oscilloscope lead attached. Measuring higher voltages than this directly may damage the instrument and invalidate the warranty. The instrument is not galvanically isolated - i.e. the ground of the internal circuitry connects directly to the ground of the host pc via the USB supply. To measure high voltages such as mains supplies use a high voltage differential probe such as the USB Instruments SI-9001 for your personal safety and to prevent damage to the instrument.​

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Msg to Doug2

Your comment about Ken is wrong and your people were not blowing smoke. I have been working on and off with Ken for years as he has worked out various issues I have had in a variety of applications. He is quite litteraly one the brightest people I have had the pleasure to work with and knows more about so many diffenent areas than most of us could ever hope too. Not only that, he is a great guy to go party with.
Sorry about the mushy stuff Ken but his comment irritated me.

i have another scope but have read with interest about
bitscope since it's early days. nice thing about BitScope
is it's open design.
there is POD interface which is basically 8 inputs which
can be used for anything you like:
http://www.bitscope.com/design/?p=expansion

here is what is inside bitscope (POD interface):
http://www.bitscope.com/design/hardware/pdf/Bs11-3.PDF

to make it 24v compatible, simplest interface is eight voltage dividers
(can be two resistor networks or even discrete resitors).
this is small enough to be put inside DB25 shell.
isolation can be done through optocouplers. just make sure
to check frequency response. for monitoring PLC digital I/O,
this is not critical (only about 1kHz) so anything will do:
http://www.cel.com/pdf/datasheets/ps2501.pdf

8 optocouplers (can be 2chips x 4opto), 16 resistors (can be 2x resistor networks)
and one DB25, done - you have 8 optically isolated channels.

Depending on your budget the DataQ DI-730 should take care of your needs. It runs about $4250 delivered, including software.

http://www.dataq.com/support/documentation/pdf/datasheets/720_730b.pdfhttp://www.dataq.com/products/hardware/di730.htm

I have used this unit exhaustively for the past three years and have never come up short. At minimum I've been able to characterize machine behaviors that aided fault isolation at later times. At best, I've discovered unknown anomalies, found intermittent problems and most important, PROVEN what is happening inside the machine. I work in the bio/pharm industry and the unit has paid for itself more than ONE HUNDRED fold. What is an hour or day of downtime cost in your plant? If you can prove when the machine malfunctioned, could you save most or all of an otherwise unusable product?

The unit has eight input channels, each completely isolated from the others and floating. Too many other features to list, but you can scan all inputs once every 50usec if needed. Both the recording and playback software are VERY easy to use. No cumbersome programming or exhaustive configuring. Similar to an o'scope, you just set basic parameters like voltage range, sampling rate, channel labels and away you go.

I could go on and on, but read the spec sheet for yourself, if interested. If you need clarification or more information, let me know.

CeCo3

I also have just purchased the Stingray

http://www.usb-instruments.com/oscillo_stingray.html

It works great, for the moment I do not need the differential probe for signals over 50V.

The only thing I couldn't do is to make it work on signals over 1M, they are saying something about 20M.

However under 1M works great

Ken,

A few more points.

• Input voltages up to 1000VDC (or peak AC) across six ranges! (The high voltage is why they had to use dual banana jacks versus screw terminals.) I can record 5v logic on one channel at the same time I'm recording 208VAC on the next, with no modules to swap out.
• Data is streamed right to the hard disk, so you are only limited by disk space.
• Playback is immediate. You can review recorded data even while the instrument is recording to the very same file.
• You can limit the file size by time or by size. You can also have it automatically open contiguous files, as each becomes full another is opened with a different file name.
• The input signals can be scaled to read in the unit of measure.
• The latest ethernet unit allows daisy chaining multiple units across long distances, great for work in mills, refineries, etc.
• The unit is extremely easy to use and is intuitive. As soon as you physically connect the laptop and start the software, you are reading active channels on your screen. Select the filename and size and ta-da, your recording. You can also append existing files.
• Quirks are few and very minor in my opinion. Banana jacks can be cumbersome at times, but I've built some interface to simplify cabling, since most of my work is 24VDC and under.
• I haven't used an oscope in the three years since I obtained the unit.
• There is optional software for streaming directly to Excel and it also supports ActiveX. Standard files can be exported to csv format.
• The unit is very reliable and accurate. No calibration issues or malfunctions so far. One USB problem found when used on an old laptop, no issues with modern HP and IBM laptops. (The USB dropped out but was detected and marked as such). Never happened to me once in 500+ (1,000 maybe?) files recorded.

I really like being able to characterize machinery motion. We've purchased various sensors and devices with analog outputs, like pressure and flow transmitters, frequency to analog converters, LVDTs, and more. PLCs do not sense every input, which limits histogram effectiveness. This unit fills in the gaps and more!

I can't speak to how well DataQ would stack up against the competition, but it is the cat's meow in my book. If it came with a holster, I would walk around with it.

CeCo3

Chuck Woodbury said:

Your comment about Ken is wrong and your people were not blowing smoke.

Sorry about the mushy stuff Ken but his comment irritated me.

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Oops you must have misunderstood my post to Ken.
1st off Ken helped me through my first major cnet installation and has helped many other people on here over the years. The comment that our rep made about ken was just that he holds a position with RA Software that is of much greater stature than sales rep (not that there is anything wrong with sales rep). They also had a interesting story about Ken's pre RA life with a competitor of RA. It was all good and the only reason I brought it up is because Ken mentioned in this post that he is in sales. Apologies to Ken if it was taken wrong.

A common mistake; Kevin Roach is the VP of Rockwell Software. Sometimes I get his e-mail, and once I got his bar bill.

Thanks for the comments, both of you guys, and also for the recommendations on cheap USB devices and the more sophisticated products too. I'll keep on shopping.

aha That is exactly what happened. I didnt want to come out and say you are the vp. lol Have a good 1

Update: After looking at a lot of inexpensive scopes and lusting after the DataQ suite of tools, and working with some old DSOs and new scopemeters, my compromise choice between features and price was the Cleverscope.

http://www.cleverscope.com/

I bought the unit that includes an 8-channel logic analyzer, and sprung for the big 8-MB memory expansion. Ordered through their USA distributor (Saelig Inc. in New York) it was shipped the next day and arrived a week later via UPS Ground.

I've been learning to use the controls, which are a little clumsy and finicky until you get used to them, and taking captures of my favorite waveform, DeviceNet CAN signalling.

When I have some field experience with using this unit, I'll post reviews and information for its applicability to common fieldbus, communication, and logic controller measurements.

Thanks, Ken for the update. Please keep us posted. Dan

Hopefully Ken RA will make a mistake in the accounting and start sending you Kevins paycheck.
Regards Alan Case