The performance of a capacitance-wire wave recorder
A capacitanoe-wire wave recorder circuit was used in conjunction with a p.t»f,e. wire probe to establish what errors are associated with using such a system for the measurement of small waves. In the experiments the probe was moved relative to the water, rather than vico versa and both photographic and electrical methods were employed to investigate the errors introduced by the meniscus, the wetting of the wire and the effects of wire thickness on the wave shapes. The electrical methods involved accurate recording of the probe movement by means of a linear potentiometer and a comparison of this movement with the wave form produced from the circuit measuring the chasige in capacitance of the probe caused by its movement in the water. The effects of increasing the operation! frequency of the recording circuit was also investigated.
‘ A water wave recording instrument for use in hydraulic models
Abstrsset. Consideration is given to the requirements of a water waveform recording instrument and to the details of an instrument designed to meet thtie requirements. The instrument has a linear calibration, and tests show that over a wide range of conditions its accuracy is to better than 2 ~. A capacitance type sensing element is used, together with transistor circuits and a pen recorder. The device is suitable for recording water waves in hydraulic models.
A water-wave measuring apparatus
Values are given for the electronic circuit required to detect, amplify and rectify a variation in resistance produced by fairly rapidly changing water levels on a pair of immersed probes, a situation met in the measurement of water waves in laboratory experiments. The accuracy of such an apparatus is checked and assessed by comparing with the usual pointer type of gauge instead of by further electrical means, and is well within the usual requirements for such experimental work.