Sunday, June 16, 2013

HART multi-variable transmitters

Some “smart” instruments have the ability to report multiple process variables. A good example
of this is Coriolis-effect flowmeters, which by their very nature simultaneously measure the density,
flow rate, and temperature of the fluid passing through them. A single pair of wires can only convey
one 4-20 mA analog signal, but that same pair of wires may convey multiple digital signals encoded
in the HART protocol. Digital signal transmission is required to realize the full capability of such
“multi-variable” transmitters.
If the host system receiving the transmitter’s signal(s) is HART-ready, it may digitally poll the
transmitters for all variables. If, however, the host system does not “talk” using the HART protocol,
some other means must be found to “decode” the wealth of digital data coming from the multivariable

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