Articles and Training

Why Is Calibration Necessary?

As components age and equipment undergoes changes in temperature or sustains mechanical stress, critical performance gradually degrades. This is called drift, and when it happens, test results obtained using measurement equipment become unreliable and both design and production quality suffers. Although, drift cannot be eliminated, it can be detected and contained through the process of calibration.

Calibration is defined as a performance comparison against a standard of known accuracy. It may just involve determination of the deviation from nominal or include correction (adjustment) to minimize the observed error. Properly calibrated equipment promotes confidence that manufactured products and support services meet their specifications.

Calibration: Increases production yields, Optimizes resources, Assures consistency, Is fundamental to compliance with international, regulatory or industry-sector specific standards that require measurements to be "traceable to national standards" and, in doing so; Ensures measurements (and perhaps prodcuts) are compatiable with those made elsewhere.

 

Why Is A Shutdown An Opportunity To Check And Calibrate Your Critical Flow Meters?

Have you ever seen fire ants excitedly swarming over a dropped sandwich? At first glance, you might believe that you were looking at a bunch of ants running around with no organization or direction to their movements. Take another look a few minutes lates and you will see that the sandwich is noticeably smaller. Each of those ants has a purpose and and an objective. They are working as a team to disassemble and transport the sandwich to a specific place. A unit shutdown has a similar apperance. First glance, shows groups of workers swarming over a peice of equipment with no organization or direction. Like the ants the worker knows what he is expected to do. Many hours of planning and preparation preceded the start of maintenace and by the time the workers swarm the unit, the job has been planned and organized down to the number of man-hours it will take to finish the task.

Although, Coriolis mass flow meters are not always included in the planning of a shutdown, this is a good time to perform preventative maintenance on the critical flow meters on the critical flow meters. You many have heard that Coriolis meters are so dependable that they should work forever with no attention. In reality, as long as man makes Coriolis meters, using man designed machines, there will be a few that perform outside factory specifications. Shutdowns are an opportunity to check and calibrate your critical flow meters. The best way to calibrate a Coriolis meter is to remove the meter, clean it and send it to a facility that has a gravimetric calibration flow laboratory. In place proving may be acceptable for applications that do not require great accuracy, but for a critical measurement, there is no substitute for direct mass to mass calibration. Master meter comparators and inferred-mass volumetric provers cannot approach the accuracy of a gravimetric facility.

If your process fluid is likely to coat or plug, check the meter for internal deposits. Deposits on the inner flow tube walls will degrade meter accuracy. Decontaminate the flow element and use a bore scope to check for deposits inside the flow tubes. If deposits are found Mass Flow Technology has had considerable success in cleaning Coriolis flow meters that are plugged.

You don't have to wait for a shut down to keep up with basic and periodic maintenance. Several valuable checks can be made on Coriolis meters during normal operating times. Flow meter zero (the flow meter output during non-flowing conditions) can be checked any time the process flow can be blocked for a few minutes. When process flow is blcoked, the flow meter should indicate zero flow. The procedure is simple; close the upstream and downstream valves and read the flow rate. The best time to check the meter zero is immediately following a batch , not before the batch. The process should be stabilized to operating conditions and entrainment should be purged. Also make sure any parameters that determine a flow cutoff threshold is set to "0.0" before checking the meter zero, return original cutoff threshold parameter.

Periodic checks can be valuable indicator for conditions that gradually grow from nothing into a big problem. Most manufactures have test points that can be measured and compared to previous checks made under similar conditions. Make a chart for recording the test points and compare the most recent checks to past checks. This may show a trend.

Mass Flow Technology, Inc specializes in calibration and support of Coriolis mass flow meters.