Table of contents

The behaviour of lead sulphide photo-conductive cells is briefly discussed and the construction of a portable radiation pyrometer using such a cell is described. The pyrometer has been used to measure flash temperatures produced by brake applications on moving vehicles. The instrument incorporates cathode-ray oscillographic presentation and its response to flashes of radiation of duration down to 1 msec. is within ±0.5 db. of the response to steady radiation from the same source. The lowest measurable temperature of a surface of emissivity 0.3 is 200° C.

It is pointed out that proportional counters as conventionally used are not precision instruments over long periods. The introduction of an α-particle group into the counter enables high precision to be attained by deriving control of the voltage applied to the counter from this group. It is shown to be possible to derive such control, compensating for leaks, outgassing or changes in electronic amplification, and yet inappreciably interfere with the intrinsic variance imposed on an initially sharp group by straggling in the ionization yield and the statistical nature of the gas amplification process. A suitable circuit is briefly described.

Control of the instant at which a circuit is opened as well as that at which it is closed must be ensured if transients are to be repeated. The apparatus described in this paper was designed to give accurate control of both these conditions and, also, to repeat the switching on and off at a controllable frequency. Electronic methods of control are used throughout. The transient may be displayed on a cathode-ray oscillograph, long exposures may be used to take photographs and the effects of altering variables in the network or the switching times may be immediately observed. The apparatus may also be used for generating very low frequency square waves to a high degree of precision.

A simple electrical viscometer has been designed enabling instantaneous indications of viscosities of liquids at any point in an industrial plant. The transmitter unit consists of a two-phase electric motor operated from single-phase mains and so designed and constructed that large variations of current in one phase are produced by small changes in viscous drag on the rotating part. The indicator unit is essentially an ammeter in one of the motor phases and is directly calibrated in viscosity units. Models have been designed for operation within pipe lines and containers up to high pressures and high temperatures (about 250° C.) and for rapid testing of samples.

A fast-acting relay is energized at frequencies in the range 0.005-500 c/s by an electronic square-wave generator. The relay has change-over contacts, independent of earth, which may be used to give exponential condenser discharges in a conventional capacitor/resistance circuit. The square-wave generator triggers a pulse unit giving a square-pulse with an adjustable time-delay. The pulse duration and delay time are both in the range 50 μsec.-50 msec. Independently adjustable pulses may be obtained from two such pulse units. Circuits for monitoring the output amplitude and mark/space ratio are given: alternative output stages for both constant-current and balanced pulses are discussed.

A method of constructing a small platinum resistance thermometer is described in which a formerless coil is contained in a fine glass U-tube. The outer glass sheath is about 6 mm. in diameter and is hermetically sealed. The lag constant of the thermometer is 5 sec. It is shown that the reproducibility of R₀ over the temperature range from -180 to 600° C. is ±0.001° C.

A simple pantographic device for attachment to the travelling stage of a metallurgical bench-microscope is described. The position of the field under view in the microscope is indicated continuously by a tracing point by means of which the disposition of the microfeatures on the specimen may be recorded. The use of the device in the examination of small metallurgical specimens is outlined.