I am working with an Li-800 gas analyzer and I am trying to extract a CO2 measurement from a serial feedback I get from the instrument. Unfortunately the documentation for doing this is limited and I am stuck. I can successfully poll the instrument and get a package of information back from it. In the “normal view” in my string indicator, the result is gibberish. When I switch to hex view I get something like this: 062A 0028 9838 3895 9884 DA76 960F DB3C 92FA BC26 8F1F D31E 8A56 291D 8104 3000 0000 0000 0000 0000 8056 362E 0000 0000 8746 0000 8921 9333 337D 5DF0 2964 000A The documentation I have says the instrument should send a 89-byte configuration packet. In looking at this package, I only see 64 bytes. The CO2 information is supposed to be encoded in bytes 64 and 65. The conversion for calculating the CO2 is: CO2 = (256*config(64) + config(65))/scaling factor; (I think the scaling factor is 8.192) I have some software that comes with the unit and it says the CO2 at the time I got this configuration package was 2264 ppm. When I successively poll the device, the bytes in the position occupied by bytes 5DF0 and 2964 change regularly. The 337D byte changes slightly and the rest of the package doesn’t change. The package is also to supposed to encode the cell temperature (51.8), cell pressure (978) and supply voltage (16.7). These are supposed to be in bytes 68-69, 72-73, and 77-78 respectively. The general conversion formula for all of these is: Parameter = o + (256*hb +lb)/s; where hb = high byte, lb = low byte, s = scaling, o = offset I am pretty sure offset is 0 for all parameters except for temperature which is -20. The scaling factor for temperature is 8.192, for pressure is 0.8192, and for voltage is 148.945. Any thoughts on this problem? Thanks.

There are two term char enables properties, one for transmit and one for recieve. Try using a property node after your read to see if there are more bytes waitng to be read. If you post your code we could help clear up some of the more subtle points. Ben

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LabVIEW

Decoding serial data.

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Hi Ravens,

the help to this property says the default is "TermChar".

Mike

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Thanks Mike.

You're right. I missed that when I read it. I had right clicked and created constant on that property node and it came up None. When dealing with subVI's, that is a good indicator of the subVI's default value. I guess for property nodes it is not.

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I modified my code so that the "End Mode for Reads" property was set to none and was able to recieve the whole message with one read command instead of two.

Thanks again to everyone for their input.

Corey

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LabVIEW

Decoding serial data.

Re: Decoding serial data.

Re: Decoding serial data.

Re: Decoding serial data.