Sensor diagnostic information: how useful is it?

15 October 2009

Tony Grassby, director of engineered solutions at Endress and Hauser explains how to make the best use of diagnostics from field devices.

Software tools take information from field devices and can send meaningful messages to engineers via SMS or email
Software tools take information from field devices and can send meaningful messages to engineers via SMS or email

Pick up a manual for any intelligent field device from any manufacturer and in most cases there will be a comprehensive list of error codes produced by the device in the event of a vast range of pre-defined, component or process-related faults or potential problems. Whilst this sounds attractive, just how useful has this functionality been to the users? Promises of advanced diagnostics and predictive maintenance information being used to avoid costly plant downtime and claims of operational expenditure savings have not always been realised.

Despite the advances made by the various fieldbus and smart technologies, today the most common method of transferring information between the various field-based components of a process automation architecture is still 4 – 20mA. In this case, all of the additional information created by intelligent sensors and regulating elements remains locked in the device itself and often not accessed until it is too late, i.e. when the device has failed and production has stopped.

In recent years, some instrument manufacturers have invested vast sums of money to develop devices that create diagnostic information that is designed to inform owners of component failure, tendency towards failure and process-related problems. However, before this information can be used in an effective way, three elements are required:

1. Intelligent field devices that create useful, intuitive diagnostic and predictive maintenance information.
2. A transportation mechanism such as digital transmission techniques conveying this information to a remote or central location.
3. A software tool that collects this information and uses it in an intelligent way. For example, a tool that identifies application-dependant error messages from critical devices, translates those error messages into meaningful text and then sends that text to the most appropriate person (maintenance or operations for example) using the best form of communication (email, text, etc).

Diagnostics available from field devices
Today a wealth of information is available from process instrumentation. For instance, an Endress+Hauser Liquiphant vibrating level switch is capable of generating error messages that not only alert the operator or maintenance staff of mechanical, electrical or electronic failure, but also process-related warnings such as fork corrosion or build-up.
A Promass Coriolis mass flowmeter, on the other hand, provides more sophisticated diagnostic information, including warnings of component failures related to the sensor or the transmitter electronics, process-related errors, such as cavitation in liquids, two-phase flow and extremes of flow velocity.

Making further use of the data
The Condition Monitoring module within Endress+Hauser’s FieldCare asset management software allows error messages produced by the devices to be sent to the most appropriate person via communication media such as email or SMS. For example, if an ultrasonic level transmitter detects that the product being measured has encroached into its blocking distance (very close to the sensor surface) then the Condition Monitoring module might be configured to send a warning to a plant operator in an attempt to avoid an overspill. If, however, the same transmitter detects that the strength of the returned echo has deteriorated, the person who configured the Condition Monitoring module might choose to send an SMS to a maintenance technician requesting to cleaning of the sensor surface as soon as possible to avoid complete transmitter failure and possible unscheduled plant downtime.

Careful selection of field instrumentation, network design and asset management software will provide the functionality described above and help to optimise your business processes.

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