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What is inter-instrument agreement and why does it matter?

What is inter-instrument agreement (or IIA)?

Inter-instrument agreement refers to how close two or more color measurement instruments (spectrophotometers) of similar model read the same color. The tighter the IIA of your fleet of instruments, the closer their readings will be to one another. While IIA is less important if you are only operating a single spectrophotometer in a single location, it is essential if you need your instruments to communicate across the supply chain. The closer (or smaller) the IIA is, the more likelihood of your colors being consistent across products, material or locations.

inter-instrument agreementInter-instrument agreement is the first step in producing consistent color quality, but it is not the only one. Implementing the right conditions and processes is also important, including sample measurement techniques and controlling temperature and humidity.

In a world of color precision, if you perform color measurements across multiple locations (different offices locally, nationally or internationally), you need to ensure the highest consistency and accuracy in your color measurement results. Often, there is little room for error.

When a company does not trust its color measurement instruments to provide consistent results, it often leads to:

  • Sending physical samples from one location to another for color verification, which takes up weeks of time
  • Mistakes discovered too late in the production process to be remedied. As a result, quality suffers
  • If mistakes are caught in time and new batches must be produced, this adds unexpected time and budget constraints

This becomes highly problematic for companies.

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Why is inter-instrument agreement important?

If you are a major brands or manufacturer, you are expected to produce color-correct products that drive sales. There are two keys to achieving this:

  1. By leveraging the use of highly precise spectrophotometers for color measurement across your supply chain
  2. By adhering to numerical tolerances for acceptable color difference for your products. These are known as Delta E tolerances.

To minimize color inconsistency while specifying or producing color, it is critical that the color measurement instruments used throughout your organization—as well as your global supply chain—produce compatible results.

How does inter-instrument agreement streamline global color operations?

Spectrophotometers with excellent inter-instrument agreement produce color measurement data that can be shared throughout the global color development process. Here’s how this process might work for a company with multiple locations. Keep in mind that, depending on the color approval process, the industry supply chain, and the number of instruments involved, there are a variety of possible scenarios:

  • Color standards are measured with one spectrophotometer in a lab in the United States.
  • The reflectance data is then shared with supply chain partners in China and Thailand.
  • Rather than remeasuring a physical standard, the supply chain partners use this “digital” standard to produce the requested color
  • The produced color is measured by the supplier and electronically sent to the customer for approval

When the lab and manufacturers are all using similar models of spectrophotometers with excellent inter-instrument agreement, it reduces the time and costs associated with producing and shipping physical samples. But more importantly, everyone involved can be confident in the digital data being communicated.

Terms related to inter-instrument agreement:

What is Delta E?

“Delta E” is the expected degree of color difference from one color measurement to another. The Delta E tolerances you set for your color measurements depend on a range of factors, among them color, material, and the intended application. You’ll find the Delta E tolerance capabilities in the specs of your spectrophotometer. The smaller the Delta E tolerance, the higher the inter-instrument agreement.

What is repeatability in color measurement?

Repeatability refers to a single instrument’s ability to give the same reading, regardless of the number of times a sample is measured. It’s important to have a repeatable measurement technique that is replicated throughout your supply chain. You can learn more about measurement techniques and factors impacting repeatability here.

What is a “close-tolerance” spectrophotometer?

The designation as a “close-tolerance” spectrophotometer is reserved for those precision instruments that are manufactured to the highest quality standards and that have the best inter-instrument agreement. The “close-tolerance” label applies only to those instruments that have very low maximum allowable variance compared to a master instrument, based on international standards.

Only a select few instrument models available in the world today produce these exceptional results without the need for adjustments based on instrument profiling. The Datacolor Spectro 1000 family of spectrophotometers satisfies the requirements of a true close-tolerance instrument with excellent performance and inter-instrument agreement out of the box.

When these close-tolerance instruments are in use throughout an organization, colorimetric data can be confidently shared between them. This also ensures that fleets of instruments can be merged or replaced without concerns of significant changes in historical results or ongoing colorimetric decisions. To avoid significant variation in measurement results, it is important to take these requirements into consideration when adding spectrophotometers or replacing old ones.

Does inter-instrument agreement decrease over time?

Not if you take the proper measures. Spectrophotometers need regular calibration and service to ensure their performance and accuracy, as well as long-term repeatability. This ensures the inter-instrument agreement of a device remains consistent over time. Many factors, including exposure to dirt and dust from the environment, can affect the instrument’s ability to deliver optimal performance. The best way to maintain the inter-instrument agreement of your spectrophotometer is threefold:

  1. Calibration: calibrate your machine at the start of each shift or before a reading. It’s also important to practice proper storage, handling and cleaning of calibration tiles.
  2. Environmental conditions: consider temperature, atmosphere, sun exposure, humidity and possible contaminants where you store your spectrophotometer.
  3. Consistency: Regular maintenance of all the spectrophotometers in your fleet, coupled with following a standardized color measurement process will help make sure your spectrophotometer is operating properly for years to come.

Technology advancements and inter-instrument agreement

With proper operation and maintenance, your spectrophotometer will provide consistent inter-instrument agreement for many, many years. Of course, there will come a time when an upgrade is necessary to continue producing the most accurate color measurements possible.

Here are some additional reasons you may want to upgrade an older machine:

  • Increased ease of use
  • Improved measurement speed
  • Renewal of an expired support contract
  • Ethernet connectivity

Success stories: Datacolor customers benefiting from excellent inter-instrument agreement

These Datacolor customers were able to benefit from excellent inter-instrument agreement to help improve their color processes.

“We are able to focus on more technical aspects of color matching and development without having to worry if our instruments give us consistent readings. Datacolor is a globally recognized platform that allows us to easily communicate with our offices across the world.” Steve Foos, Assistant Vice President of Research & Development at American Colors, Inc.
Still have questions about inter-instrument agreement? Contact our team to learn more.

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