The use of fibre optics in viscometry

A semi-automatic viscometer, for determining the specific viscosity of a solution, is described. The use of photodiodes, instead of light-activated switches, means that the circuitry is very simple, a relatively expensive timer/counter being replaced by an ordinary, inexpensive, digital stopclock. The use of fibre optics has a threefold purpose: (i) photodiodes, with a larger surface area than light-activated switches, can be used, and thus, the sensitivity of detection is increased; (ii) one light source replaces the two LED lamps; (iii) the whole apparatus can be immersed, without sealing, in a thermostatically controlled bath as all electrical components and wiring are remote, the only connections being made via the optical fibres which are simply air-coupled to the light source and to the viscometer.