An automatic and continuous recording balance. (The odén-keen balance.)
J. R. H. Coutts, Edward Mortimer Crowther, Bernard Augustus Keen, Sven Odén · Proceedings of the Royal Society of London Series A Containing Papers of a Mathematical and Physical Character · 1924
Abstract There are very many experiments in which it is essential to have an accurate record of a change of weight, with time, and the treatment of such experimental data, frequently involves a measurement of the rate of change of weight with time, or even of the second differential. Until 1915, when one of us (S. O.) devised a suitable apparatus, the only means whereby an experimenter could follow with any accuracy the course of such a change was to make the weighings himself as frequently and rapidly as possible. This is a very tedious and fatiguing process, especially if the experiment is at all protracted. In the original form of self-recording balance, control was effected by an automatic discharge of a small steel ball of known weight into one pan at the instant that the increasing weight in the other pan became equal to the total weight of the balls already in the first pan. The time of discharge of each ball was automatically recorded, hence it was possible to obtain a record of weight as a function of time by plotting these values and drawing a smooth curve through the points. An upper limit to the accuracy of such a record is set by the weight of the smallest sphere that can be employed in practice in the ball-discharge mechanism, and it is evident that greater detail and accuracy of the record of increasing (or decreasing) weight can be secured by some form of electro-magnetic control, which will allow the recording of smaller changes of weight than is possible with metal spheres. The present paper consists of an account of an apparatus evolved for this purpose that is reasonably simple, and reliable in its action.