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Interfacing with Proportional valve with HART

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Interfacing with Proportional valve with HART

We have a valve with HART control that we are currently controlling with an NI 9265, current output module. This has worked fine but we're wanting to get positional feedback from the valve. Previously we had used a USB HART Protocol Modem (https://microflx.com/products/din_hart?variant=792035747) This worked fine on an older system where we were using an SCXI Chassis. But the cRIO module has a max load of 600 ohms and when we put the required resistor for the modem to work, the combined load of the valve and the resistor were too much and we weren't getting full scale output. 

 

Now I am looking into using the AM-9898 module. However this module only reads in the current loop, it doesn't have a current output. Could I use this in conjunction with the NI 9265 or do you think I would run into the same problem? Thank you for any help or input. 

 

Also the valve controller is a metso nd9000 I believe. I'll have to look and see if I can find the information on the load resistance.

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Re: Interfacing with Proportional valve with HART

I found the information for the valve. It has a load resistance of 475 ohms so that plus the 250 ohm loop resistor put it over the 600 ohm max load of the current output module. So unless the AM 9898 has a lower resistance I don't think it will work.

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Re: Interfacing with Proportional valve with HART

Hi CaveJohnson,

 

The AM 9898 has a RX resistance of 272 ohms (under "HART Specification", here). It can read and write on the HART bus. It doesn't allow direct control of the current as an analog output though, but if you keep going through the ND9000 valve controller would that move the valve itself?

Andrew T.
"His job is to shed light, and not to master" - Robert Hunter
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