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Steve G

HART signal to standard input

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This may not be the right place to post this but sense I am using AB hardware I will post it here. I have some new flow meters that came in and they seem to have come in with a HART 4 to 20 signal. They were not requested with this type of signal and the hardware I have on the system is a 1794-IE8. My question is can I wire the 4 to 20 HART signal to a standard 4 to 20 ma input and will it work, or am I going to have to add another input card for these flow meter. I have only once had to deal with HART and it was on a system that was already installed and I just had to add some status bits into the software. Thanks for any help on this topic

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HART (Highway Addressable Remote Transmitter) are Analog Transmitters which can be configured/calibrated while functional within a process using the established analog circuitry to carry the configuration/calibration software data. I believe you could wire them up to a "stock" Analog Input module and use the signal just as you would do with any analog transmitter, of course without the HART functionality which could be provided only by a HART Analog Input module. Edited by dmargineau

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HART is a high-frequency protocol overlaid on top of a standard 4-20mA signal, so you can take it directly into a standard 4-20mA analog input. Not sure if you need any kind of filter, but I don't think so.
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Thanks for the help, I went and installed it and it works fine, no filter needed. I also called the manufacturer of the flow meter and they told be the HART protocol was only used for the configuration device you can buy with the unit and a standard 4 to 20 ma input was just fine to use. Thanks again everyone.
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The HART signal rides on top of the 4-20 mA, and doesn't interfere with it. It's very handy for configuring field instruments while they're in service. Usually you use a hand-held calibrator which you simply clip onto the 4-20 mA circuit the way you would with a Voltmeter. Your 4-20 mA devices won't even see the HART signal. You can read up on it at www.hartcomm.org

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HART communicates at 1200 bps without interrupting the 4-20mA analog network.  It allows a master application to get two or more digital updates per second from a smart device. If you need a HART to Modbus converter (RS-232/485/422), you can check this one out: http://www.icpdas-usa.com/i_7570.html?r=dora

 

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