Calibration Standards

What are calibration standards?

Calibration standards are devices that are compared against less accurate devices to verify the performance of the less accurate devices. The standard’s accuracy varies depending on what is being calibrated; most professionals recommend using a calibration standard that is at least four times more accurate than the device being calibrated.

Why do we need calibration standards?

Imagine a trip to the grocery store where you buy a pound of hamburger. How do you know that the pound you buy at one store is the same weight as one you can get at another? The answer, of course, is that the meat is weighed before it is packaged. But how do we know that the scales used to weigh the meat are delivering accurate measurements? We trust this is true because periodically the scales are calibrated with more accurate weights and then adjusted to be within their specifications. The process of comparing one scale against a more accurate instrument continues, with the measurements becoming more and more accurate, until we reach the “top” of the measurement pyramid, which is the kilogram. 

This is a simplistic example of traceability. Traceability is how we refer to a chain of measurements that range from the lowest level of the calibration pyramid all the way up to the SI standards. A traceable calibration is one performed as part of an unbroken chain of measurements that can be traced back to an SI unit. Each measurement also has an evaluation of the measurement uncertainty, to quantify the quality of each measurement. More information about traceability, the SI, and the calibration pyramid is available on the Fluke Calibration About Calibration.

Having traceable measurements allows us to understand and trust in them. Traceable measurements also enable reciprocal agreements between countries; these agreements facilitate fair international trade.

For more information, see our page on Why Calibration Is Important?.

What are the standards used for calibration?

Calibration standards can be found in primary calibration laboratories around the world. Primary laboratories perform the most accurate calibrations and are often classified as National Metrology Institutes (NMIs). NMIs can be found in almost every country, with a network of less precise working laboratories that branch out into a system that forms the measurement infrastructure of each country. 

Primary calibration laboratories are typically accredited by an organization that has been independently qualified to review and certify the labs’ quality, accuracy and processes. Most large countries have one or more providers of accreditation, and countries often agree to trust each other’s measurements based on their trust in the respective accreditations.  More information about accreditation is available on the Fluke Calibration About Calibration page.

What are the requirements for calibration standard?

Measurement devices typically have specifications for their measurement ranges, accuracies and uncertainties. You can find this information in the product manual. The manual also often specifies what is required to calibrate the device. Typically you are going to use standards that are at least four times more accurate than the device you want to calibrate. You’ll want to balance the need for accuracy against your budget. And you’ll want to look at other product features like usability, form factor, and ability to calibrate multiple devices. Depending on your workload you might also want to look for a calibration standard that can be automated with calibration software.

What types of calibration standards does Fluke Calibration manufacture?

Fluke Calibration manufactures multiple types of calibration standards:

Electrical calibration standards

• Voltage standards
• AC/DC transfer standards
• AC measurement standards
• Resistance standards
• Ratio standards
• Current shunts
• Frequency standards

RF calibration standards

• Low phase noise reference sources

Temperature calibration standards

• Standard platinum resistance thermometers
• ITS-90 fixed-point cells
• Maintenance apparatus
• Liquid nitrogen comparison calibrator
• Resistance bridges
• Standard resistors

Pressure calibration standards

• Piston gauges
• Deadweight testers
• Pressure controllers and calibrators
• Pressure comparators and digital pressure gauges
• Portable/handheld pressure calibrators
• Flow calibration standards

Gas flow calibration standards

• Reference flow monitors
   

What are NIST standards for calibration?

To ensure consistent and reliable calibrations, the National Institute of Standards and Technology (NIST) has established several standards for calibration. They provide guidance on the calibration process of many types of equipment. NIST also administers an accreditation program for calibration laboratories, offering an unbiased evaluation of a calibration labs technical qualifications and ability to complete specific calibrations or tests. 

What is the ISO standard for calibration of equipment?

When people talk about calibration standards, they don’t always mean physical instruments. Sometimes they might be referring to quality standards or regulations that specify calibration. For example, ISO 9001 is a quality standard that requires certified companies to calibrate their measurement equipment, plus document the processes and procedures involved. ISO/IEC 17025 is the quality standard that calibration laboratories use to ensure they produce valid results. ISO/IEC 17025 is the quality standard that calibration laboratories use to ensure they produce valid results.

Where can I find more information?

The Fluke Calibration About Calibration page is a good source of general information about calibration.

Keep Learning

• Choosing the right pressure standard selection guide 
• Establishing a primary temperature calibration standards laboratory 
• A Primary Calibration System for the Support of High Performance Gas Flow Transfer Standards 
• A basic but comprehensive overview on Calibrators
• The Fluke Calibration Education Hub