Understanding when and where to calibrate your flowmeters
It’s a simple enough conundrum: Failure to calibrate flowmeters can negatively impact performance, while calibrating too frequently can result in excessive costs without providing a benefit. So, when and how do you calibrate to best effect? The answer is, with planning and understanding so that you can make informed, proactive decisions rather than being reactive.
With flow measurements, the industry standard is to calibrate annually, even though that might not be necessary. Often, it’s a ritual with no scientific basis behind it, other than it being as long as operators are willing to tolerate the risk of a potential problem. Some flowmeters require calibration only once every 3-4 years. In other circumstances, more frequent calibration, possibly even monthly, may be required to maintain a safe, efficient, or regulatory-compliant operation. Calibration intervals might also fluctuate based on usage or historical performance.
New instruments and technologies, combined with careful planning and study, can allow plants to calibrate flowmeters at an optimum frequency, resulting in improved operations and cost savings.
So, when to calibrate? Step 1 is developing a flow calibration plan that follows best practices. Our Endress+Hauser whitepaper, “Best Practices for Flow Calibration Management” covers the issues in developing such a plan, including performing a plant wide assessment of all instrumentation, including flowmeters, ranking the latter according to four levels of interest from highest to lowest – product-critical, process-critical, safety-critical and non-critical – and establishing acceptable tolerances for each device.
Download the Endress+Hauser whitepaper, “Best Practices for Flow Calibration Management”. Click here
When to Calibrate?
Setting up such a flow calibration plan often requires assistance from the flowmeter manufacturer and/or a qualified service provider to identify the optimal calibration frequency. The end-user must use this advice and apply it based on particular service conditions, functions of the meter and their own experience.
Calibration frequency depends on the criticality and maximum acceptable tolerance, as well as the nature of the product being measured, normal usage pattern (continuous or intermittent), any clean-in-place (CIP) considerations, the severity of process impacts, the type of flowmeter (contact or non-contact), and the unit’s accessibility for calibration. In some cases, it may only be possible to access a flowmeter during a complete process shutdown; in other cases, a flowmeter might be readily accessible.
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In a new plant, the flowmeter calibration frequency is usually based on expected operational parameters and advice from the flowmeter manufacturer. In an existing plant, the frequency can be based on historical experience and previous documented calibration performance and processes that yield better results. In either case, quality, regulatory or safety requirements may override the manufacturer’s advice or historical data.
Once a calibration plan has been in effect for a few years, the instrument management software used in formulating the plan and storing performance data takes on a bigger role. Each time calibration is done, new data is recorded and stored in the database. This data shows the status of the flowmeter before and after calibration, and it may indicate it does not require calibration as often as previously assumed.
Where to Calibrate?
For calibration, flowmeters may be removed from the process and shipped to a calibration lab. Calibration can also be done at the user’s site, using a portable flow rig. A portable rig does not provide the same accuracy as a lab, but does offer convenience and speed. Depending on plant topology, many measuring points can be quickly calibrated with minimal process downtime.
Calibration labs typically handle larger size flowmeters with larger flowrates. Portable flow rigs can handle flowmeters up to a maximum of 2” (rig), but larger sizes can be calibrated in-line with master meters. The results of on-site flow calibration are still traceable to recognized national standards and the turnaround time is reduced to hours versus days or weeks. For example, Endress+Hauser’s on-site flow calibration is accredited in accordance with ISO/IEC 17025. Endress+Hauser can calibrate up to 2” on site and up to 4” at our Burlington, ON office.
For a comprehensive overview of the capabilities of third party providers of calibration services, download our Endress+Hauser whitepaper, “Instrument Calibration as a service”. Click here.
These are key considerations in opting for lab versus on-site calibration.
- Best accuracy
- Turnaround in days or weeks
- Suits larger calibration range – 1/24” to 12” and larger
- Usually costs more than on-site calibration
- Good accuracy
- Faster turnaround than a lab, usually in hours
- Suitable for 2” and smaller, using a calibration rig – or 3” to 4” with in-line calibration with master meters
- Usually costs less than laboratory calibration
Thanks to advances in flowmeter diagnostics and instrument management software, the increasing availability of nearby calibration labs and portable rigs, and the willingness of instrument vendors to assist users with calibration, setting up and implementing a flow calibration plan based on best practices is easier than ever.
For instance, a Wisconsin food and beverage plant was having compliance difficulties after failing an audit. They realized they needed specialized support. Working with the flowmeter manufacturer, they performed an assessment of 300 flowmeters. Next, the calibration plan was established and frequencies determined. After calibrating all devices, all flowmeter data was stored in a calibration management software solution. Now the plant is able to easily access performance information, including calibration data, history and certificates.
Such solutions can help find that Goldilocks balance – calibration intervals that are not too frequent or infrequent, but just right.