Instrumentation Monitoring

OK. How about an ASI13 analog interface card plugged into the back of an old Apple II desktop computer, running Lotus 1-2-3, all obtained off the junk heap previously enjoyed equipment market then? A bit 1982, though it will work, because it did then.

Seriously, there are thousands of ways of doing it. All that will come from this forum is whatever other readers have used recently. What readers don't have, because it isn't in the original post, is a list of what is available locally. Throw out some suggestions, perhaps?

For blind (after the fact) monitoring, a google search for 'datalogger' will pull up numerous options.

For visual real-time monitoring, there's the old stand-by, process recorders. Check out Honeywell Trendview. Its 10 ohm input resistance means that a 4-20mA signal can be run in series with it and another device and not overload the loop circuit. Or the signals can be paralleled as voltage from the dropping resistor on the present device's analog input card.

You won't know for sure if isolation modules are needed until you connect the circuits. If the power supply for 2 wire loop powered field transmitters is grounded, then you probably will need isolation modules. If the power supply is floating, probably not. Connecting a 2nd device in a loop acts like a ground loop tester and is really good at reacting to ground loops and its the final say.

There's lots of PC analog input cards with software. Google is your friend.

Be warned that a lot of them are high speed input cards, more suitable for use in the oscillographic time domain than for process data. Process data can appear very noisy because of the lack of low pass filtering and the use of sample and hold A/D's rather than integrated A/D conversions.

Many are single ended inputs which is practically begging "please, give me a loop isolator" because it is a prime candidate for ground loops. Even some differential inputs have very low common mode rejection, sometimes not even spec'd. Like my father said, there's nothing someone can't make cheaper (and you end up paying for it one way or another).

People have predicted the death of process recorders for years, but they're still used because they do what they do well and reliably.

Enjoy your shopping adventure.