Technical Service

What is the Inter-Instrument agreement?

Please note that the following explanation is general and not only matches to Konica Minolta measuring instruments but also to those of other brands!
The inter-instrument agreement is the basic value for all certifications of spectrophotometers. As physically there is no standard existing for colour, the main issue is getting traceable and repeatable measurement results which are within a specific tolerance range for each model of an instrument series.
Thus instruments of the same type should measure the same values. Technically this is not 100% possible, therefore the inter-instrument agreement values are used to show the differences between single instruments.
The centre (master) value of inter-instrument agreement is determined by measuring a specific quantity of instruments of the first production lot. Actually we cannot just talk of only one centre point. For getting more precise information about the agreement between multiple instruments, a set of 12 BCRA tiles is used to establish the inter-instrument agreement. By using master bodies, which are very close to this centre point, BCRA tiles are measured and the average of this measurement data is used as centre value for inter-instrument agreement.
Depending on the design, for example the size and opening port ratio of the used sphere, the tolerances for inter-instrument agreement are slightly different for each type of measuring instrument. In addition, the centre points for different models are not necessarily located in the same position of the colourimetric diagram.
The following drawing is just an example for the relations of different instruments. This example only shows the inter-instrument relation for one colour.

As you can see the circles which shows the agreement between instruments of same type are different in size. Instrument type B shows the best inter-instrument agreement, whilst instrument type C shows the worst results! The size of these circles represents the inter-instrument agreement values and depends on the construction of the instrument.
In addition, the centre points of the circles are not located in the same position. Also these centre positions depend on the construction of the measuring instrument. Due to these different locations of the centre points, it is not (or only within a specific tolerance) possible to compare absolute measuring results of different instrument types!

About certificates and local differences

So far we have talked about important issues for calibration service, but of course the result must be a certificate showing the relevant values and standards. Of course, these are different for each instrument type. During the previous years, Konica Minolta has improved the certificate contents (upon customers' request) to a level which is accepted for customers ISO9000 certification process.
As the used standards as well as the requirements are slightly different in each country, there are small differences in the certification at each local service facility.
In addition, tolerance levels for certificates made at service stations are different from certificates made during on-site service. These differences are due to the temperature-controlled environment, which is used in Konica Minolta service facilities to reach highest accuracy tests. To keep the level of on-site tolerances in a reasonable range, Konica Minolta uses a special temperature compensation system for on-site measurements of inter-instrument agreement.