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Emerson develops two-wire Coriolis meter

An EDITORIAL REPORTS product story
Edited by the Processingtalk editorial team Nov 27, 2008

Emerson has announced a two-wire version of the Micro Motion Coriolis meter.

For many years, engineers installing Coriolis flow transmitters, recognised as the most accurate mass and volume flow technique available for the typical process liquid flowlines on any plant, have suffered from the complex wiring requirements.

Originally, these units had a nine-wire connection between the transmitter unit and the sensor, but then with integral transmitters the wiring was simplified to just the external four wires, two for power and two for the data.

The extra power supply was needed to drive a large enough tube vibration, which would generate sufficiently large Coriolis signals to be extracted from the background noise.

Emerson's two-wire version of the Micro Motion Coriolis meter uses MVD technology, which uses front-end digital signal processing to enable the measurement of much smaller Coriolis signals against the background noise.

In addition, the meter operates on 20mA loop power, but is in fact a 12-20mA transmitter, allowing more power to be channelled into the meter drive circuits than would be possible from just 4mA.

Called the Micro Motion two-wire Model 2200S Coriolis transmitter, the unit is capable of working as a conventional 20mA Hart loop transmitter, with an intrinsically safe option, so achieving a very powerful and simple replacement for any other liquid or gas flow transmitter on gas, liquid or slurry lines of up to 2in in size.

It offers +/-0.1 per cent of flowrate accuracy on liquids, +/-0.35 per cent on gases, and a liquid density accuracy of 0.0005g/cm3, with full Hart diagnostics.

Emerson have introduced a barrier and interface converter unit for use with the Model 2200S that can translate the 12-20mA signal into a conventional 4-20mA signal at the control room interface.

The first test installations have been successfully trialled, for example a 15mm unit was used on reactor gas purge lines at Momentive Chemicals (previously GE Silicones) in the USA, and another installation was at LyondellBasell in Illinois.

While the US promotion for this unit seems mainly to stress the savings resulting from not having to run four cores to each 'new' measurement point, in Europe, on existing plants, the main benefit will be that the two-wire Coriolis can slot into the same two-core plant wiring used for any other flow transmitter, making an accurate Coriolis instrument a viable option as a replacement unit for any existing loop-powered flow transmitter.

Emerson see the Micro Motion two-wire Coriolis as suitable for use in the chemical, petrochemical and refining industries, for continuous process and mass balance applications, and with a 316L stainless enclosure for offshore and marine applications.

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