Logo der PTB - Messen, Forschen, Wissen
Production sequence of Si-spheres and interferometrical determination of the sphere volume

Conformity of Length Measuring Machines

Working Group 5.45

Length measuring machines

In many cases, trade and industry make up accounts on the basis of length measurements or their combinations (area, volume) on commodities of the most different kind. In these cases, the measuring instruments must have been approved for verification or their conformity must have been certified in accordance with Directive 2004/22/EC. The testing and research activities of the Working group are focussed on these conformity assessments or approval procedures in accordance with the Verification Act for log wood and choirometers.

To top

Types of measuring machine

A focal point are the length measuring machines for textile area-measured materials, for which it is today even possible to measure the length of extremely flexible materials with relative uncertainties of less than 0.3%. With the aid of the laser Doppler technology, the limits of mechanical scanning methods were overcome, and length measurements with low measurement uncertainty became possible even on tuft-coated textiles. The test of a novel measuring method based on optical position correlation has already shown that it will be possible to further reduce the measurement uncertainies. Another instrument group serves for the measurement of restiform materials (in particular cables). Here it has become possible to increase the feed rate of the product to be measured to up to 17 m/s, while complying with the maximum permissible error on verification for the length measurement. In future, the length measurement on light pipe cables will also be performed automatically, for which new technologies are to be expected. These will again require the development of new test procedures and associated regulations.

Length measuring machine for flexible textiles

Volume measuring device for packages

Of great importance are measuring instruments which allow the area or the volume to be determined by non-contact optical-electronic screening. To these instruments belong the area measuring machines which are mainly used for irregularly limited leather surfaces. Here, the relative measurement uncertainty could be reduced to less than 1%, and the feed rate of the product to be measured could be increased to up to 1 m/s.

Trunk wood measurement by means of ultrasound scanning

In the case of volume measuring instruments, the required dimensions are obtained by scanning - on the basis of which the volume is calculated. Examples are measuring instruments which serve to determine the smallest enveloping cuboid of packages for aviation. In timber industry, novel measuring instruments - the so-called log wood measuring facilities - have lately been used to an increasing extent. These facilities measure the length and diameters of the logs automatically and calculate - on the basis of these measurements - the volume to be invoiced in business. By virtue of EC regulations, carcasses must be classified with choi-rometers which, in Germany, are subject to mandatory verification. The instruments, which work with opto-electronic systems or ultrasound, measure the thickness of specific layers of the biological product to be measured and determine from it the trade classes for the price to be paid for the carcass.

Invasive Choirometer