Verification, validation and calibration
Verification, validation and calibration are different but interrelated processes that are often confused. Ask three people what these terms mean, and you will get three different answers.
At a basic level, the three terms may be defined as follows:
- Calibration ensures the measurement accuracy of an instrument compared to an known standard
- Verification ensures the correct operation of equipment or a process according to its stated operating specifications
- Validation ensures that a system satisfies the stated functional intent of the system
Calibration: Is it accurate?
Flow calibration is a two-fold process of measuring and adjusting the accuracy of an instrument relative to a known measurement standard called a calibration standard. This process begins with comparing the measured flow of a meter or controller to that of the calibration standard. Following this assessment, the meter or controller is then made to conform to the readings of the calibration standard within the stated accuracy specifications.
A primary calibration standard is directly measured against a reference standard provided by a bureau of standards, such as NIST. These standards tend to be very expensive. A secondary, or transfer, calibration standard is directly measured against this primary calibration standard in the lab and then serves in lieu of the primary standard in the field. Alicat mass flow meters and pressure gauges purchased with the “HC” (High-accuracy Calibration) option can serve as NIST-traceable secondary calibration standards in the field. An Alicat portable that is used as a transfer standard becomes a portable rapid calibration lab.
We apply this same concept to our line of Portable Calibration Units (PCU), which combine three battery-powered flow meters of complimentary ranges in a single case, all with High-accuracy Calibration. This instrument is the big brother of a single portable meter, able to calibrate flow devices across a very broad array of flow ranges.
Verification: Is it working correctly?
Flow verification is a procedure designed to ensure that your equipment or process is still doing what it was designed to do from the beginning. In the context of the automotive industry, you might use a flow meter to verify that the total consumption of air per minute in automated painting robots is still what it was when you bought them. This is often an internal process that focuses on maintaining the performance of a device or process over time, as opposed to a mandate or regulation coming from an outside source.
Our series of mass flow meters, both wired and portable, are excellent choices for in-line verification of process flow rates and absolute pressure readings. For volumetric measurements, the low pressure drop of our Whisper Series provides an unobtrusive way to measure volumetric flow rates with minimal effect on the flow rate being measured.
Validation: Is its system function satisfactory?
A validation process ensures that the components of a system function together to meet the need or intent of a customer or regulating body. The aim of validation is to ensure that the components of a system work together to produce the intended result for which the system was designed. Whereas verification focuses on the right operation of a process (or product) itself, validation tends to focus on the right output of the process.
For example, the EPA closely regulates the output of stack gases at power plants and refineries. Whereas flow verification might be used to confirm the maximum flow rate of a valve in the analyzer system, flow validation would be used to ensure that the analyzer system as a whole delivers a throughput that allows a level of gas analysis that meets or exceed the EPA requirements. The emphasis in validation is on the functioning of a process or whole system to meet the needs within a larger system.