Table of contents

An instrument for gauging electrodeposited nickel layers within the thickness range 0.2 mil to at least 1.5 mil is described. It utilizes the local thermal e.m.fs set up when a heated metal probe is brought into contact with the coating. The final design, now in commercial use, has high stability effected by minimizing temperature drift in the probe and by selecting materials of appropriate thermoelectric properties.

The influence of the differing thermoelectric properties of various commercial nickel deposits upon the accuracy of measurement has been evaluated. Extensive industrial trials are reported. With subtrates of steel, copper-plated steel and copper-plated zinc alloy, amongst 1400 individual measurements of nickel thickness about 90% were within ±0.1 mil.

A simple apparatus is described which can be used to plot the field contours of a laboratory magnet, even when the instability of the field in time is comparable with the variations in space. It consists of two super-regenerative oscillators which produce signals at the nuclear magnetic resonance frequencies of the proton samples in their tank coils. One sample is fixed while the second scans the magnetic field, and the field difference between the two probes is presented in frequency units on an electronic counter. The method can be extended to make the field mapping operation completely automatic.

A circuit is described which enables the automatic calibration of a magnetic field to be carried out. A marginal oscillator, frequency controlled by one of eleven quartz crystals mounted in a motorized turret tuner, detects nuclear magnetic resonance signals. These signals activate a pen recorder and also trigger a control circuit which advances the turret tuner to the next channel.

An ultra-violet absorption optical system has been constructed for an air-driven Phywé ultracentrifuge. The intensity of a parallel beam of ultra-violet light transmitted by the solution in an ultracentrifuge cell is measured by scanning the enlarged cell image with a photomultipiler. The electronic circuit permits the measurement of both transmission and optical density.

In conventional apertometers accuracy is limited by parallax between the effective aperture stop and the scale image. This is overcome by the use of a projection system in the device described.

This note describes a sensitive thermometer, which measures temperature differences directly. The circuit is a simple Wheatstone bridge with thermistors as sensing elements. By choosing the resistances in a certain ratio to each other, equal temperature differences give galvanometer currents equal to within 0.6% of each other, for an absolute temperature change of 6 deg C.