Multivariable transmitters, which measure more than one process variable in a single instrument, are growing in popularity among end-users. Typically these transmitters measure pressure, differential pressure, and temperature. As such, a multivariable transmitter can actually replace three single variable transmitters. In many cases, they use these values to produce a mass flow measurement.
Multivariable transmitters can be used to reduce the need to buy a separate flow computer to perform the flow calculation. If individual pressure and temperature transmitters are used, the value outputs are sent to a flow computer that performs the flow calculation. For multivariable computers, the computing power of the flow computer is typically brought on board through the multivariable transmitter, which also performs the flow calculation. The trend toward multivariable transmitters can be expected to continue in the DP transmitter andflowmeter markets. These products typically sell for less than it would cost to buy the transmitters separately.