Technical Information

Basic concept

Measurements are always wrong... It's just a matter of how wrong.

All products are calibrated in our internal laboratory, which of course is done in accordance with DIN EN 10204, as well as the guidelines of DAkkS (National Accreditation Body for the Federal Republic of Germany). Our personnel is highly trained and particularly careful to perform precise calibrations in line with individual customer needs.

The calibration of temperature sensors is always necessary, when because of either standards or legal instructions a return to international standard is required. Quality Assurance norms like the DIN EN ISO 9000 require a regular calibration for all quality relevant measurement and testing means, under the return to the realisation of the SI-Units serving national and international norms. Furthermore a calibration can be required , when smaller marginal limiting deviations are necessary as instructed in the DIN EN 60751 or for testing of the long term behaviour of a temperature sensor.

Calibration means determining the measurement tolerance at the complete temperature sensor or the measurement chain (temperature sensor with transmitter).During calibration no technical intervention takes place at the device under test (DUT). For display measurement devices the deviation between the display and the value of the measurement category accepted as correct, is fixed. No modifications at the apparatus like e.g. zero point re-positioning occurs.

During calibration of temperature sensors one decides between two processes: calibration at the fixed points and calibrations according to the comparison method.

1. Calibration at fixed points

Calibration on fixed points are predominantly used only for Pt-Standard resistance thermometers according to ITS 90 (International Temperature Scale 1990).

Fixed points are phase equilibrium pure materials (solidification-, melt or triple points).

Triple points are tempered in a liquid bath or a vertical multiple zone oven. Fix points can consist of an open or closed glass vessel which contains the appropriate material (water or metal) in purest form > 99,9999%.

The materials, fixed point temperatures and design of the cells are described in the IST 90.

The calibration and fixed points occur between 0.01% (Triple point of water) and 921°C with a measurement inaccuracy of 0,5mK to 5mK. The fixed point calibration involves a high time consuming and apparatus input, so that their use is reserved only for state test centres (PTB) and a few DKD calibration locations.

2. Calibration according to the comparison method

Most industry and temperature sensors are calibrated according to the comparison method.

During the calibration the devices under test are put into a liquid bath or a test oven.

As bath liquids apply:

Liquid Temperature range
Ethanol -100°C to 0°C
Water 0°C to 99°C
Silicon oil 50°C to 250°C
Salt mixture 180°C to 630°C
Tin 250°C to 630°C

Comparison measurements in test-ovens can be carried out up to 1600°C. The devices under test and the comparison standards are inserted into a zone with even and constant temperature. The devices under test are so inserted into the test facility that an error through heat dissipation is impossible. Before the calibration the devices under test are tested for function and insulation according to DIN :EN :60751. As standard, precise resistance thermometers or thermocouples are used which are calibrated by a DKD or State Testing Station. After the stabilisation of the baths or the ovens they are compared to the Normal. A document (calibration certificate) is issued showing the results.