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Sensors, Actuators

Get flow measurement right the first time

Understanding, monitoring and controlling flow rate are essential elements to the viable operation of production systems and must be done right. See five key flow considerations.

By Brendan Robson December 30, 2019
This is an Endress+Hauser display from Process Expo 2019. Courtesy: CFE Media and Technology

Understanding, monitoring and controlling flow rate, as part of industrial processes, are essential elements to the viable operation of production systems. There are many elements involved in getting such measurements right and the hazards of getting it wrong can be severe for the plant and the workers.

Fundamentally, the selection of appropriate measurement technology and its cost, accuracy and proper use will affect the result. For example, a recent measurement audit of an alcohol bottling plant found classic manual procedures were in place for both sampling and for offline density measurement, subsequently used to infer the alcohol by volume (ABV) of the product.

Unknown to the plant operators, the Coriolis meters used to measure flow rate also were capable of measuring density. Using these Coriolis meters to measure both flow and density would allow immediate online alcohol content monitoring along with prompt action and enhanced product control.

The reluctance to change is a powerful barrier throughout industry. However, this should be balanced with an understanding of the available technology, including the importance of flow measurement, and its assessment in a cost-benefit analysis according to requirements. When operating a process that relies on measurement systems for monitoring productivity, control or safety, the ability to prove the accuracy of the measurement system is vital.

This requires an understanding of measurement uncertainty, calibration and traceability, as well as a management system incorporating a measurement policy and a maintenance schedule. This leads to confidence in the measurement process and the result.

To achieve the target accuracy, which is critical to trade and commerce, most countries have a dedicated regulatory framework that supports the national measurement infrastructure and is designed to facilitate and regulate good measurement practice.

Metrology traceability, including flow determination, plays a vital role in national infrastructure since accurate results and confidence in measurement are impossible to achieve without it.

Traceability is the technical proof a measurement device has the appropriate pedigree, normally through calibration records, referenced back to a national standard.

The traceability chain

As we move up the traceability chain toward a given measurement standard, the uncertainty in measurement reduces (becomes more accurate). However, to achieve lower uncertainty it is necessary to invest more money in the system by way of increased capital, maintenance costs and experienced staff. This is important to consider, as the most accurate system is not always the correct solution for a given application.

Owing to the cost penalty associated with achieving and maintaining low uncertainty, the requirements for a given application need to be considered prior to system design and component selection.

Despite the work invested in maintaining and regulating the NMS, when performing a measurement audit, a common finding relates to instruments not installed or operated in accordance with the requirements, or in some instances are no longer traceable to the appropriate standard. It is not uncommon to find flowmeters in service where the operator has no record of when the device was calibrated and no planned maintenance for the system.

What is restricting industry from investing in such powerful diagnostic tools and traceability? A key factor is the required level of measurement uncertainty. If we consider the oil and gas petrochemical industries, the needs usually are well established. These organizations typically have dedicated metering departments to support the measurement of flow for hydrocarbon-based products of high value, where even small uncertainties can lead to large financial exposure over short timescales.

Another key factor is these industries are regulated much more tightly than others, due to the fiscal value of the metered product. The same degree of stringent regulation does not often apply to flow measurements in other industrial environments. So, companies in sectors such as food and beverage, power or chemical may rarely undertake complete flow measurement audits and instrumentation is often underutilized. Conversely, the development and application in medical and pharmaceutical areas are potentially a matter of life or death.

Five key flow considerations

Regardless of the industry, there are five key considerations that need to be asked:

  1. Do you understand the uncertainty in the measurement systems that you require for your business, and can you prove it?
  2. How does your measurement system perform over time?
  3. How frequently do you calibrate?
  4. Do you have any past performance data that would allow you to improve the performance or establish an optimal calibration period?
  5. Are these points recognized in your quality system?

Traceable and good measurement practice is critical in achieving accurate and repeatable flow measurement. However, selecting the appropriate solution depends on understanding the operation and the measurement uncertainty required for a given application. This requires a fundamental understanding of metrology as well as the process to which it is applied. Given the sophistication and capability of modern flow measurement technology, such systems may not simply measure flow rate but also provide powerful diagnostic capability and valuable data. This can provide insight into both the efficiency of the measurement system and the effectiveness of the process, which has the potential to yield substantial commercial benefits including improved monitoring and performance.

Brendan Robson is a project engineer at TÜV SÜD National Engineering Laboratory. This article originally appeared on the Control Engineering Europe website. Edited by Chris Vavra, associate editor, Control Engineering, CFE Media and technology, cvavra@cfemedia.com.

MORE ANSWERS

Keywords: flowmeters, process safety

There are many elements involved in getting flow measurements right and getting them wrong can have severe consequences.

Traceability is the technical proof a measurement device has the appropriate pedigree, normally through calibration records, referenced back to a national standard.

Traceable and good measurement practice requires a fundamental understanding of metrology as well as the process to which it is applied.

Consider this

How well-versed is your company in good flow measurement practices and standards?


Brendan Robson
Author Bio: Brendan Robson is a project engineer at TÜV SÜD National Engineering Laboratory.