Calibration, validation, and verification with mass flow meters

Calibration, Validation, and Verification

Calibration, validation, and verification 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
  • Validation ensures that a system satisfies the stated functional intent of the system
  • Verification ensures the correct operation of equipment or a process according to its stated operating specifications

Calibration: Is it accurate?

Flow calibration is a twofold 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.

Alicat PCU open to use for calibration, validation, and verification

PCUs use three flow meters with complementary ranges and high-accuracy calibrations to create a portable calibration standard.

A primary calibration standard is directly measured against a reference standard provided by a bureau of standards, such as the National Institue of Standards and Technology (NIST). These standards tend to be very expensive, so 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. Mass flow meters and pressure gauges calibrated to high accuracy can serve as NIST-traceable secondary calibration standards in the field. Portable flow meters used as transfer standards can act as portable, rapid calibration labs, for in-field calibration.

We apply this concept to our Portable Calibration Units (PCUs) and combine three battery-powered portable flow meters of complimentary ranges into a single case, all with high-accuracy calibrations. The PCU is the big brother of a single portable meter, able to calibrate flow devices across a very broad array of flow ranges.

Validation: Is it functioning satisfactorily?

Whisper-Series mass flow meter for process verification

Whisper-Series mass flow meters can be used for process verification with minimal effect on the process flows.

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.

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.