Calibration of Lambda Apparatus for Determination of Thermal Conductivity for Thermal Insulation Products—Guidance Worked Out by the European Keymark Expert Group

Abstract

Today it is a demand in Europe that manufacturers of insulation material determine the thermal performance of the thermal insulation products during production on daily or weekly basis. This demand has created a need for easy to use lambda equipment by operators with only basic knowledge of how to measure thermal conductivity. An instrument that meets these criteria is a Heat Flow Meter (HFM) apparatus, which in principle is a “black box†instrument, where determination of the thermal conductivity is controlled by software and the controllable parameters are reduced to thickness and parallelism of the measuring faces. As HFM apparatuses are now one of the most common types of lambda equipment used by manufacturers in the Factory Production Control (FPC) throughout Europe, this has created a need for guidance on how to ensure verification of the stability of measurements for this equipment. This paper describes the guidance for calibration of a HFM apparatus for determination of thermal conductivity for insulation products. The guidance has been worked out by the Keymark Expert Group based on long term experience and is available at the web-site: www.insulation-keymark.org [1]. Calibration of thermal conductivity equipment is an important element in the FPC for a manufacturer, for notified bodies, and for registered laboratories in the Keymark scheme. The rules for this task are defined in the European standards for “Evaluation of conformityâ€, EN13172, and in the Keymark scheme rules. In former times a HFM apparatus was not always stable and the calibration constants had to be changed from time to time. With today’s technology, this should normally not be done anymore, except in a case where such action has proven needed. This paper will outline those scenarios. Calibration is defined as the determination of the deviation from the true value for a measuring instrument and a comparison to a more accurate instrument, where is used for the verification of the lambda read-out. Besides the verification of the lambda read-out the calibration includes determination of the temperatures of the measuring plates and the thickness.