Page 5 - Industrial Technology EXTRA 21st June 2021

Originally, most plant operators took a reactive first and most obvious is that we want to check the
approach, where essentially a device was allowed to device’s health. If it is going wrong, perhaps
break and then was fixed. This was an expensive suffering a fault that is causing it to stray outside its
method as in certain cases it could lead to the calibration parameters, this could affect production
whole plant tripping out, extended down time and a quality by causing problems such as inaccurate
rush to find replacement parts or devices. For blending, dosing or billing. The other reason, even
example, in a batch production environment, such more important, is ensuring that processes remain
as mixing orange juice concentrate with liquid in a in a safe condition.
food and beverage plant, the failure of a flow meter
would not allow the right proportions to be mixed to Using the data
produce the correct quality of product and the At a very basic level, taking advantage og these
process would need to stop until the problem was capabilities comes down to how we communicate
resolved. with the device. Although most measurement
This is bad enough in the above batch method devices are digital, many applications continue to
but in a petrochemical process, based on 24/7 use the tried and tested 4-20mA current loop rather
continuous production, allowing a temperature than digital communications networks. For
transmitter to simply fail could be potentially example, all ABB’s 4-20mA measurement devices
catastrophic. Things got better in the 1970s to 80s, also offer HART communications, a bi-directional
when preventive maintenance came to the fore, communication protocol that provides data access
with devices maintained to a schedule. Even this between intelligent field instruments and host
was highly manual, with equipment being checked systems. The communications link carries the
by staff walking the line to note which devices were process values, like flow rates or temperature.
reading or behaving as expected and which ones It also gives access to the device’s diagnostics
needed attention. data, such as its operational status. Many advanced
Over the last few years, the concept of predictive digitally enabled measurement devices will offer
maintenance has become ever more popular, with sensor checks including internal connections, an
the aim of trying to prevent failure events in the indication of sensor memory failure and an internal
future. Although predictive maintenance is still a electronics check. With communications in place,
form of preventive maintenance, it uses actual device interrogation is the next step. There are two
condition-based data to determine when to perform methods for interrogating device data.
maintenance, as opposed to a pre-determined The first is inbuilt condition monitoring and
schedule based on historical information. diagnostics based on the NAMUR NE 107
By using condition monitoring of equipment, we standard. To make things easier for technicians and
can know more about exactly when to schedule other process personnel who need to deal with
maintenance and prepare for it in advance, for alarms, NAMUR NE 107 categorizes internal
example, ordering spare parts. We can also make diagnostics into four standard status signals —
use of the increasingly rich data available from failure, function check, out of specification and
measurement devices to identify exactly what went maintenance required, each of which can also
wrong and derive strategies or techniques to prevent contain greater detail. For example, with a failure
the same problems occurring in the future. There signal, can the failure be traced to the device, or
are two main reasons for condition monitoring. The alternatively, is the process itself at fault?

June 2021 • INDUSTRIAL TECHNOLOGY EXTRA • p5