Photometer made in Jena

Pulfrich, a man before his time: in 1923, Prof. Dr. phil. Dr. eng. h.c. Carl Pulfrich, the first head of the Department for Optical Measuring Instruments of Carl Zeiss Jena, was not aware of either ISO or EN ISO 9001:2000. The International Standards Organisation ISO was not even founded until 1947, nor was the new standard for quality management systems. It was not published until 2000. Pulfrich was 77 years ahead of his time. He was already practicing 77 years earlier what was to become a standard in 2000.

He required that the customer`s demand on the photometer be produced (EN ISO 9001:2000, 7.2.1)1. He took these demands as the basis of his development. He had the customers validate the result of development. One of the examples of his customer-oriented approach in instrument development is the Pulfrich photometer. The measurement problem was the determination of the so-called black and white content of grey and coloured dress materials. In the textile industry, this was done by using a method from Wilhelm Ostwald. The method was based on a visual comparison of the fabric sample with a grey-step scale developed by Ostwald.

This grey-step scale made of pigment dyes comprised 24 steps representing equal intervals of sensation. The two ends of the colour scale were represented by a white barium oxide plate and deep black silk velvet. The customers from the textile industry demanded Pulfrich minimize the subjective factor, this provided for the possibility to measure intermediate values. This enhanced accuracy of the measurement. By 1923, a prototype of the photometer was demonstrated for Ostwald. It was eventually given to a dye house for "industrial testing". The tester confirmed to Pulfrich, "with the instrument the target striven for is to be regarded as achieved". Following Ostwald`s grey-step scale, Pulfrich named his development "step photometer". It´s more common as the Pulfrich photometer. This name was abbreviated in the Zeiss manufacturing plant and referred to as "PuPho". The accompanying pictures shows the original Pulfrich photometer; shows the scheme of this instrument.

The Pulfrich photometer is a double-beam photometer with optical zero adjustment. The human eye functions as a detector. The term "zero adjustment" is used as the two partial images produced above the eyepiece are adjusted to equal brightness by means of diaphragm B2. The measuring position of diaphragm B2 is a measure of reflectance. This can be read directly from scale M.

With additional units, Pulfrich opened up new applications for his photometer as well as new markets. It was used as a nephelometer, colloidometer, fluorometer, and as colorimeter. On this colorimeter model, the measuring diaphragm is replaced by a liquid layer, the height of which is adjustable. "Spectrophotometric" measurements were achieved by the use of colour filters. The "PuPho" colorimeter model made in Jena in 1960 is shown in the accompanying picture. The Pulfrich photometer was produced in Jena for almost 40 years. In 1962 it was followed by the SPEKOL® spectrophotometer.

 

Literature and Illustrations source:

EN ISO 9001:2000, December 2000; Carl Pulfrich: über ein den Empfindungsstufen des Auges tunlichst angepasstes Photometer, Stufenphotometer genannt, und über seine Verwendung als Farbmesser, Trübungsmesser, Kolloidometer, Kolorimeter und Vergleichsmikroskop. Zeitschrift für Instrumentenkunde, 1925, 45th year, No. 1, p. 35-44, No. 2, p. 61-70, No. 3, p. 109-120., VEB Carl Zeiss Jena: Technisches Handbuch für optische Messgerüte 1960; Hundert Jahre optische Analysenmessgeräte aus Jena, 1975; VEB Carl Zeiss Jena: Technisches Handbuch für optische Messgeräte, 1960.

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