Hi people,
I need to select equipment for measuring and recording temperature in a database. I like the products from opto22, but I was wondering: do you know of any cheaper, smaller-brand, or chinese clones or alternatives? The devices should be able to accept different instruments, and interface to ethernet. Thanks for any pointers.
Z.
What temperature ranges are we dealing with here and what type of sensors? How many points do you need to record, how frequently? That sort of detail matters here as the scope for responses in so seemingly a simple request is wide enough to cover a very large list of possible responses.
My work is mainly in the 4K to 300K range of temperatures and we use Carbon and Pt100 elements in most of those measurements. Some of our measurements are recorded at 1ms intervals due to the nature of the behaviour of one of the fluids involved.
Once you improve the detail of your requirements a suitable answer will certainly be forthcoming.
Paul,
What fluid at 4K, helium? At one time at RCA Labs, our project had a helium liquefier. We used enough to justify its installation.
Jerry
Yes. My current workplace has it's own Cryo-plant as we use so much liquified Helium that the suppliers would not be able to keep track. There are a number of baloons in our roof-space where we store the warmed gas once it has done its cooling duties ready for re-liquification. It tends to be a fairly continuous process and we don't let very much go to waste.
My bit is one of the user processes.
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The requirements are fairly modest: 0 to 150 Celsius range, 1s sampling rate aprox. The important facts are that: it needs to be cheap, it needs to provide ethernet access. The project is for a friend who owns a small firm that produces waste water treatment machines. Right now its all mechanical, gauges and valves: first step is to record temperatures on-line. I am interested in hearing about cheaper alternatives to the opto22 Ethernet SNAP boxes. I've built a few microcontroller based devices which send data via serial ports, but ethernet is a major task for a DIY project.
Z.
OK, in that case you may find that buying a single SBC and adding some conditioning circuits (Op-Amp/Isolation, multi-plexing etc) yourself may be the least expensive option. Look at
I expect that Pt100 probes would be your most likely sensor. The correction formula is relatively easy if you need super accuracy but the curve of a Pt100 is very nearly linear anyway that you may be able to live with the slight dip in the middle of the range.
When you have logged all the temperature profiles you need and understand his waste process well enough you can then re-use the board as part of an overall embedded control system for the equipment.
Some of the microcontroller vendors sell module boards with ethernet hardware and some of the ethernet software already in place, for example:
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Because PRTs are much more linear than thermocouples and the range is relatively small, the number segments needed probably won't exceed 2. Even so, I prefer quadratic interpolation to linear with more segments because the slope discontinuities are smaller and can be made zero if that's important (although the article doesn't explain how).
Jerry
Paul, thanks for your answer. The mpe boards are nice. I am afraid that the industry is moving fast towards this kind of embedded boards with mini-operating systems and I/O and I know little about them. I need to do my homework.
Z.
You are welcome.
If you need any help with the Forth environment on the MPE boards I, and many others, also hang out at comp.lang.forth. There are a number of books that will also help to get you thinking in the right frame.
I know that there was a Forth based system that used the Opto22 modules as well. However, things are going towards the smaller footprints of embedded controllers which give you significant increases in power of expression of the solution to any problem.
If Ethernet had not been in your list of requirements I might have steered you towards another Forth based Vendor who aslo does H8 based boards and system components.
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