Danw,I really appreciate your feedback
Thanks
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QUOTE=danw;874895]HART is primarily used for configuration, reading and writing parameters via HART, using a HART modem with a software app like Pactware or a handheld communicator like Emerson's Flex.
Pactware needs each device's DTM file that is specific to the device. Presumably, all the configuration parameters are accessible via HART. Some of the DTM files will read, log and display the primary variable. If the secondary or tertiary variables are assignable from a pool of variables, that sort of task would be accomplished through the DTM. I'm pretty sure that the DTM for Siemens pressure transmitters will read the secondary value (body temperature).
If you want to read HART variables from a field device for logging or control purposes, it's a different ball game.
01. Analog input reads HART
The PLCs, PACs or DCSs that do so use a very high end analog input and the software/firmware implementation to get the data and tag it. I am unaware of a low cost option for this kind of HART performance.
2. HART multiplexor (mux)
Multiple HART devices reside on a series network 'loop', each device with a HART ID number. Typically, the mux controller polls each device in sequence and provides the data to the real world as valies in a Modbus slave/server register. Mux's go for $4k-$5k.
3. HART multidrop
Multiple HART devices reside on a series network 'loop', each device with a HART ID number. Typically, a PC program uses a HART modem to address each device as needed.
Not terribly popular because of the relative slow rate at which can HART read variables from multiple devices (about 2 readings per second).
If you just want to goof around with reading HART values, then a HART modem with Pactware with a pressure transmitter that uses the primary HART variable for pressure and the secondary HART variable for body temperature.[/QUOTE]