Smart devices: configuration or calibration?

31 March 2015

Control Engineering Europe spoke to Jan-Henrik Svensson, VP sales & marketing at Beamex about the issues surrounding the calibration of smart devices. 

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In a recent survey undertaken by Beamex, almost two-thirds of its customers stated that they are using, or were planning to use, WirelessHART somewhere in their plant.

With more and more plants employing smart devices, Jan-Henrik Svensson believes it is vital that users are properly educated regarding the impact that smart device technology can have on calibration. 

“There are people who take smart devices into the field and configure them in the belief that they are actually calibrating the devices. However, setting ranges and certain parameters inside the device is not a calibration operation. Calibration of a device requires the accuracy of the device to be compared to a known reference. “If you are only configuring a device you are not introducing a known reference, so there is no guarantee of an accurate measurement,” warns Svensson.  “There is really no point in taking a measurement if you do not know whether you are measuring it correctly.”

The output protocol of a transmitter will not change the fundamental need for calibration and even the best instruments and sensors will drift over time, especially when used in demanding process conditions. Regulatory requirements, quality systems, safety systems, and environmental standards all require accurate calibration to be undertaken and it can also help ensure that the process is working optimally.

An important feature of a smart transmitter is that it can be configured via the digital protocol. Configuration of a smart transmitter refers to the setting of the transmitter parameters. Configuration needs to be done via the communication protocol and, in order to do this, it is necessary to use some form of configuration device – typically also called a communicator – to support the selected protocol.

Although a communicator can be used for configuration, it is not a reference standard and cannot be used for metrological calibration. Configuring the parameters of a smart transmitter with a communicator is not in itself a metrological calibration and will offer any assurance of accuracy. 

According to international standards, calibration is a comparison of the device under test against a traceable reference instrument and documenting the comparison. Although the calibration formally does not include any adjustments, potential adjustments are often included when the calibration process is performed. If the calibration is done with a documenting calibrator it will automatically document the calibration results.

To calibrate a conventional analogue transmitter the input can be generated or measured at the same time as measuring the transmitter output. In this situation calibration is straightforward. A dual-function calibrator will be able to process transmitter input and output at the same time, or alternatively two separate single-function calibrators.

However, with a smart transmitter, the output is a digital protocol signal. Obviously the transmitter input still needs to be generated/measured in the same way as with a conventional transmitter. However, to see what the transmitter output is, it is necessary to have a device or software that is able to read and interpret the digital protocol. This can make calibrating smart devices a very challenging task. 

Solving this issue was one of the biggest drivers behind Beamex adding configuration capabilities to its calibrators. “The MC6, for example, employs a configuration capability which is able to match the configuration capability to the instrument, with the metrology element on top. It can also set and verify configuration with a calibrator,” said Svensson.

Beamex MC6 is a high-accuracy field calibrator and communicator that offers calibration capabilities for pressure, temperature and various electrical signals. The MC6 also contains a full fieldbus communicator for HART, FOUNDATION Fieldbus and Profibus PA instruments. The device has five different operational modes, which means that it is fast and easy to use, and allows the technician to carry less equipment in the field. The operation modes include meter, calibrator, documenting calibrator, data logger and fieldbus communicator. In addition, it communicates with Beamex CMX calibration software, enabling fully automated and paperless calibration and documentation.

If you are measuring a tank level, it may not matter whether the tank is 65% or 68% full. However in other applications accuracy could be far more critical. For example, when measuring the temperature of a shutdown circuit for steam turbines or a nuclear reactor, accuracy is vital.  Further, in the pharmaceutical industry ingredient and dosage measurements need to be accurate and consistent in every batch produced,” continued Svensson.

The ability to configure and calibrate devices with one instrument is also a bonus in light of the growing shortage of knowledgeable calibration engineers and technicians in the workplace. “Many of the staff undertaking calibration and configuration tasks today have a much wider range of responsibilities and often do not have the depth of understanding and skill needed to accurately effect instrument calibration and taking into account any configuration uncertainties,” said Svensson. 

To overcome the calibration skills gap, Beamex calibration technology allows calibration tasks to become more of a plant level decision undertaking, offering the tools and systems to make calibration decisions in the field and helping companies to run leaner operations, while ensuring a plant continues to run safely and remain compliant.  Good calibration techniques can also help drive quality and/or process improvements.

Beamex offers the tools to provide a simple measurement pass/fail in the field, based on the process.  Some of the user interface designs now also guide users to make the right connection and assist them to wire devices properly. “We are keen to ensure that the people using the calibration tools are given the right level of knowledge to allow them to use the tools properly. We have a very active professional services team that can deliver active on-site training for users of our devices,” concludes Svensson.

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