Water utilities with highly successful monitoring programs tend to share a common trait: when it comes to calibration, they have a well-defined plan that emphasizes frequency and tracking. However, when done properly, this process is time-consuming and often leads to unnecessary labor and downtime.
Flowmeter “calibration” is a term that’s often used generically, and in many cases, people say it when they are referring to verification. The latter is a qualitative process to ensure a meter is within the original tolerances of the wet factory calibration, but without going so far as to remove it from service. Verification is used to demonstrate the flowmeter meets specific requirements defined by the customer or manufacturer. Reliable verification can be accomplished using two different methods: either via an external handheld or simulator or by an internal verification. Both methods are based on traceable references; however, internal verification is based on traceable and redundant references built into the flowmeter’s electronics.
True calibration involves quantitatively comparing measurements made by a device against a known, traceable standard. Thus, with inline flowmeters the device must be removed from the line and sent back to a NIST traceable facility to be recalibrated, which is both time consuming and costly and, in some instances, not possible.
Verification does, however, offer water managers the confidence to leave devices in place until a true calibration necessitates removal. The biggest impact of this occurs with flowmeters, which provide critical information used in operations and compliance.