4-20mA > HART

Hello,


I have a module that gives a 4-20mA signal without HART interface. The customer uses HART and wants to be able to get both the 4-20mA signal and the value via HART to their DCS.

Any ideas for black boxes. I have found repeaters but the way I understand they need a HART interface in the transmitter side also.

for you to send the module information to your customer, your module must have a Hart interface.

Nonuke is correct. Hart performance is built into the transmitter. If the transmitter does not have HART, it never will, with the sole exception of Honeywell's ST700/800 pressure transmitters with swappable comm modules.

I'm no expert, but every HART interface I have seen includes a 4-20 mA loop input. The 4-20 mA loop is the circuit on which the HART protocol is superimposed; you simply can't have HART without having a 4-20 mA loop.

I think that MrQ is looking for some kind of 're-transmitter' that will take in 4-20 mA on one side, then re-transmit the 4-20 mA as well as a HART signal containing the 4-20 mA value as the Primary Variable.

That sort of device might exist, but I can't see a reason for one; if the analog signal is the only input, then the HART data can only serve to duplicate or confirm the existing signal.

I suppose in somebody's mind this might be a way to improve 'signal confidence' by sending the same data both as analog and digital.

Ken is correct. That is exactly what I am looking for.

I'm very skeptical that you're find what you're looking for.

Only a tiny fraction of the AI's are capable of stripping off the HART data, mostly DSC's, a few high end PLC's or PAC's, so the HART market for analog is a fraction of the HART market for configuration.

The market for a device that has already suffered a D/A-A/D conversion which then takes the analog value (with that error) and converts it to HART and retransmits it, is your client, and your client alone, as far as I know.

The market for HART is
- configuration via HART
- multiple variables, like a coriolis meter or multivariable DP flow meter
- diagnostic data available via HART
- HART multidrop, primarily for diagnostics
- the occasional guy who knows that some minor error is avoided by getting the HART value and not getting the error from the D/A-A/D conversions (1 in 100,000)

Good luck looking, but in 20 years of HART stuff, I've never heard the request before, nor seen a commercial device that does what you're looking for.

I am also sceptical and realize that this is odd....

Another solution would be an analog output module with 4-20mA output and HART. Preferably for CAN bus.

Ideas?

An analog output with HART for a PLC is available. Allen Bradley's ControlLogix has a HART AO card.



The vendors are going to have to have a PAC product or be a player in the process world.

Remember the PLC card is a HART master, talking or reading from a HART slave field device. I'm not sure that that fits with what you're asking for. Field devices are always HART slaves, polled or written to by the DCS/PAC/PLC master.

I'm not sure an AO card HART master will communicate successfully to another HART master AI card.

I can't help you on CAN, it's not a player in the process world.

Found this.

http://nivelco.com/download/pdf/pdf4g04a0602a.pdf

Congratulations! Talk about finding a needle in haystack!
The -8 4-wire model looks like it will do the job.

MrQ said:

Found this.

http://nivelco.com/download/pdf/pdf4g04a0602a.pdf

Click to expand...

Nice find, but would it be cheaper to just replace the transmitter with one that is has Hart build in.