Simultaneous measurement of voltage by two computers

[dMemphys]

Hello everyone,

For a test bench we're finalizing, we have a few sensors (PT, TC, etc...) that are amplified to -5/5V by Delmation modules, multiplexed and recorded on a computer by an ADLink PCI card. As some of these measurements are critical, we need to double the recording devices (the computers, in case one fails during a test). What we did was to buy a second computer and equip it with a second multiplexer card (ADLink). Basically, we now have two computers that are interogating the same sensors right after they've been amplified by the Delmation modules.

Our problem, as we should have anticipated, is that both cards, while they're sampling the input, interfere with each other. Spikes appear when one card takes a measurement and the measurements display a sort of overall beat.

We were wondering if there was an easy way to solve this problem. I guess that, in a way, we should try and galvanicaly isolate each card with the input?

Thank you for your input!

 

[MikeHalloran]

Never mind the spikes; the receivers could affect each other's DC readings as well.
You need to synchronize the computers so that they sample in alternation, _and_ disconnect the idle computer from the circuit during the active computer's measurement. It's not clear that there's a way to do that with what you have.

Maybe there's a fancier multiplexer.

Maybe you could forget the analog multiplexing, and make each measurement station independent, running an embedded webserver, or at least dumping their numbers onto a net or a bus in some digital form.

Or you could just run with the one computer, but have a twin or two ready and warmed up and set up for fast hot-swapping.



Mike Halloran
Pembroke Pines, FL, USA

 

[djs]

Can you find a signal conditioner with dual outputs?

 

[dMemphys]

Hi!

Thank you both for your answers, they actually helped me direct my search. Dataforth, from which we got the signal conditioners, actually already sells redundancy hardware. This hardware actually seems to be dumping all the measurements on a ModBus network and, hence, allows multiple acquisitions from different computers.

Shame I did not learn about this sooner ^^

Thanks again!

 

[GregLocock]

You seem to be adding redundant redundancy and not necessary redundancy. In my experience the analogue sensors and wiring and plugs and amps are the weak point.

Cheers

Greg Locock


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