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Product category: Flowmeters and Flow Sensors
News Release from: Emerson Process Management - Flow Division | Subject: DeltaV
Edited by the Engineeringtalk Editorial Team on 05 June 2002

Process plant sensors with added
intelligence

New breeds of process transmitters are emerging which take advantage of the growth of intelligence and computing power available in field devices.

New breeds of process transmitters are emerging which take advantage of the growth of intelligence and computing power available in field devices These transmitters monitor several different variables at once, and can deduce enhanced measurements to improve processing and quality control

The ability to transmit digital information around a modern process control system, using such information networking techniques as Foundation fieldbus, has led to rapid dispersal of the plant control intelligence and functions back into the field devices.

The PlantWeb digital plant architecture uses and interconnects field-based intelligence centres - where intelligence is based in the control valves, differential pressure transmitters or flow measurement devices themselves.

The skills of modern process automation systems - for example the DeltaV batch control system from Emerson - is to access and collect information from these intelligence centres, and use their own software capability to present this information to the process operator and plant manager in the way each of them expects to see it.

The opportunity for the designer of intelligent instruments is that these equipments can do so much more, because they have extra intelligence and an efficient communications system - still based on a two wire pair of interconnections.

Micro Motion design engineers have accepted this opportunity with both hands - and extended their Coriolis mass flowmeter technology to the extremes.

The new electronic processing available for use with these sensors is multivariable digital technology, named because the sensor is no longer limited to measurement of just one variable.

The Coriolis technique itself allows separate measurement of mass flow rate of the fluid, and actual fluid density within the sensor, as two independent variables.

Adding a temperature sensor gives another process variable, making three totally independent measurements stored in the device, along with measurement of time.

Simple - almost to be considered conventional - signal processing allows the intelligent electronics to compute the fluid volume flow rate (as the mass flow divided by the measured fluid density), and to select the required units for measurement of mass flow rate, density and volume flow rate.

Internal batch and accumulated totalisers can display and transmit these flow totals.

Preprogrammed event points can be set in the electronics to register when batch totals, flow rate alarms or density limits are exceeded, as well as quality monitors for the instrument performance.

The intelligence built-in to the Micro Motion MVD electronics processors also introduces digital signal processing into an industrial instrument - the first time this has been done with a Coriolis meter.

Digital signal processing used at the earliest possible stage in measuring the Coriolis signals allows more efficient signal processing and better signal to noise ratio in the measurement circuits.

This leads to more accurate data and extended measurement ranges, and enhanced zero stability, using the sort of technology applied to space telescopes and modern telephone systems.

For the process plant operator this means increased performance and reliability, plus a wider range of application from a single instrument.

Further benefits come from the other data that can be stored in the memory of the unit - data from other plants or laboratory measurements.

The accumulated experience of years of measurements on process fluids can be stored in a microprocessor chip.

This can relate the density of a liquid to the salt or sugar concentration, or the alcohol content, or the solids loading.

Standard formulae and relationships are known and preprogrammed within the memory, enabling the instrument to give measurements that are familiar to the food process operator, such as Brix or Baume.

But new customer and process specific data can be configured on site: data that are specific to that process perhaps, and requiring commercial confidentiality.

This can be configured in the memory by the plant operators themselves.

Such data typically might require at least a temperature proportional correction, which is simple to achieve within the electronics using the fluid temperature, already measured within the device.

Often the relationship between measured density and sugar, or alcohol content, or other process variable, can be so complex that the microprocessor chip has to store a matrix of these curves at different temperatures - and tracking the fluid temperature measurement, the software can select the appropriate curve for any normal plant situation.

The simple analogue 4-20mA output can then be configured to transmit a signal relaying the computed alcohol concentration, or whatever the required plant parameter represents.

The following outputs are available from an MVD Coriolis meter: mass flow rate; mass flow total (batch or accumulated); liquid (fluid) density; temperature; derived volume flow rate; volume flow total (batch or accumulated); derived process concentration; derived solids content; corrected density figure; and volume flow corrected to standard conditions.

An example of this derived preprogrammable relationship technique applied to sugar dosage in baby food comes from Nutricia in Holland.

Recently they replaced some positive displacement flowmeters with Micro Motion meters in order to dispense batches of dextrin-maltose sugar solution into the process tanks, using mass flow measurement.

Both the temperature and concentration were process variables that had an impact on batch quality, but using mass flow measurement led to significant improvements in process control accuracy and repeatability.

However, when the dextrin-maltose came from a different supplier, the quality and sugar level changed, so that simple mass flow was no longer sufficient to maintain control.

The Micro Motion Elite sensor used at Nutricia measures not only the mass flow rate, but also the actual density of the batch being delivered.

By applying a standard Brix algorithm from within the electronics, the solution proposed was to correct the delivered mass flow for the actual sugar concentration, as deduced from the density, using standard tables.

However the dextrin-maltose did not follow the standard sugar curves, and a series of trials were needed to establish the correct sugar content to density and temperature relationship, which was freely configured on the plant within the memory.

The system now allows the correct process quantities to be mixed, independent of the raw material quality, delivered sugar concentration and temperature.

Using the Micro Motion Coriolis meter, the operator can select the desired net sugar content to be loaded into the batch vessels, and production has achieved an improved end product of consistent quality.

Over 400,000 Micro Motion Coriolis meters have been supplied since they invented the first practical flow measurement device in 1977.

Because of the lack of moving parts, the stainless steel materials, and the obstructionless nature of the pipework, the meter was applied to food and slurry applications immediately.

Food applications were further expanded after the development of a straight tube version of the meter, the T-Series, that achieved EHEDG certification and 3A authorisation for hygienic applications.

Micro Motion produces Coriolis flowmeters in line sizes from 3 to 150mm, for gases as well as for liquids and slurries/pastes.

There are different styles and accuracy levels available for the sensors themselves, and different capabilities built-in to the different ranges of electronics.

The most accurate sensor is the "Elite" range, which is also the most expensive.

At the other end of the cost scale, the R-Series meter was launched in 1998, aimed at the general purpose flow measurement market.

With less precise and versatile measurement capabilities, this meter was positioned as the lowest priced Coriolis meter available, with a price similar to conventional flowmeters.

The R-Series is now outselling all the other ranges available, in terms of numbers of units.

Last year this R-Series model also gained EHEDG certification after tests at TNO, and also 3A authorisation for hygienic applications.

Mondomix - the Dutch manufacturer of "Swiss" roll production plant - has adopted the Micro Motion R-Series: the company replaced conventional magnetic flowmeters with Coriolis and saw an efficiency improvement in their manufacturing processes immediately.

Another pan-European and worldwide company that chose Micro Motion over the competition was APV - because APV know they can count on Micro Motion products meeting global standards, and that product support is available for food plants anywhere in the world.

The Micro Motion MVD electronics technology applied to the different Coriolis meter sensor styles gives major enhancements to the performance and output capabilities of this style of flowmeter.

But the process is not limited to flowmetering techniques: various other devices have enhanced performance and interfacing intelligence, best accessible when used on modern fieldbus networks, but providing improved measurement performance on any plant.

Control valves are the most critical component of any process system, and probably are the target of the most maintenance expenditure on any plant.

The Fisher Fieldvue digital valve controller DVC6000 monitors control valve total travel, and therefore wear, to alert operators to valves with potential maintenance requirements.

The valve controller stores the operating characteristic of the valve as built, during initial test, and on plant: this data can be accessed and compared to the current performance to identify degradation.

The Rosemount Analytical 1055 chlorine analyser takes the input from a pH meter in the same water stream to self-calibrate the chlorine measurement electrode, again using a look-up calibration matrix.

Similarly the Rosemount Analytical Model 225 toroidal conductivity analyser is used to monitor CIP cleaning processes: the special "unfilled" Peek sensor material contains a temperature sensor to allow compensation of the conductivity measurement up to 130C.

The batch canning of brewery products is a high rate process, and product quality monitoring is particularly important after flushing out or sterilisation procedures.

Online analysis is now possible with a real-time mid-infra-red process analyser, which uses a dedicated computer to monitor all the spectra of components present.

Experiments with the Rosemount SpectraProbe are extending this capability to let the instrument identify each type of beer from their spectral fingerprints.

The opportunities now available to use built-in intelligence in field devices is favouring the multiparameter, complex sensor.

The modern bus communication systems allow this data to be presented to the operator, or accessible by remote interrogation, to produce far more efficient plant operations.

Even without bus communications, these intelligent devices are now easier to apply, and provide better, more relevant measurements for the food process engineer.

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