JAN-FEB 2019

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24 INTECH JANUARY/FEBRUARY 2019 WWW.ISA.ORG Smart transmitters enable smart sensors Integrating digital technologies made instrument transmitters smart, with instrument sensors following in their wake By Steven J. Smith P rocess instruments consist of two main components: a sensor and a transmitter. The sensor is sometimes part of the instrument assembly, as with some pressure instruments, but is more often separate, as with analytical instruments, such as those used for pH measurement. Before sensors could become smart, transmitters had to gain intelligence by adapting digital technologies. It would not have been practical, or sometimes even possible, to connect a smart digital sensor to a simple analog transmitter. Industrial instrumentation has progressed significantly since the 1970s, when the vast majority of instruments simply had a single 4–20 or 0–20 mA (analog) output proportional to the process variable. Some sensors had the inherent ability to measure multiple process variables, but they required multiple analog outputs to access this additional information. With an ana- log transmitter with a single analog output, secondary variables remained stranded, as did data regarding the configuration or health of the instrument. The process variable was relegated to a dedicated analog signal transmitted from the instrument over two wires to an indicator or control system, with a multidrop configuration. Working with these instruments required direct access to the device and Figure 4. A technician can connect a smartphone to an instrument, such as a flowmeter, and access the meter via its integrated web server. The same procedure can also be used for access from a remote PC or tablet.

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