Patent GB-443485-A (GB)
Title: Improvements in means for detecting, observing, measuring, indicating, recording orutilizing minute movements
Filed: 1934-06-26
Abstract: 443,485. Automatic control of variables. WIGAN, E. R., 2, Brandram Road, Lee, London. June 26, 1934, No. 18812. [Class 38 (iv)] [See also Groups XIX and XXXVII] Apparatus utilizing minute displacements for the control of a device such as a thermostat comprises a first " contact gauge " surface associated with the solid body the movement of which is under investigation and a " feeler gauge " surface carried by a resilient member to which is imparted a steady controlled state of vibration of small amplitude the frequency of which is near to the natural frequency or to a, harmonic of the system comprising the resilient member, so that when the two surfaces are proximated a, new unstable " vigorous vibration " manifests itself characterized by a marked change of amplitude which may be used to operate a relay. Fig. 1 shows the application to a gauge. The resilient element 4 which is maintained in oscillation by an electromagnetic system 3 is mounted on a support 5 and carries the " feeler gauge " surface 1 and a mass 2 adjustable in magnitude and position so that the natural period of vibration of the system 1, 2, 4, 6 is near the fundamental frequency of the forces developed on the element 4 by the element 3. A jar-sensitive contact 6 consists of a small light spring carrying a mass at the free end which it holds against a contact 6<11> carried by the member 4. This can be adjusted to be unaffected by the steady vibrating member 4 but to break contact momentarily when " vibratory contact " occurs between the " feeler gauge " surface and the " contact gauge surface of the body under investigation. The contact 6<11> is only used in controlling subsidiary apparatus. Controlling subsidiary apparatus. Fig. 2 shows a relay 8 operated by the breaking of contact 6. A source of current from a battery 11 or from a half-wave rectifier 13 is supplied to the circuit containing the contact 6, a choke coil 9, and a resistance 10 across which is the relay 8 and a spark quenching circuit 12. Two other relay spring circuits are described in which the relay is controlled by the " vibratory control " and the contact gauging surface. Circuits controlling the vibrator. In Fig. 4a, the winding g of the magnet 3 of Fig. 1 is in circuit with a current meter m and resistance a. The current is adjusted by a potentiometer b the displacement of the body being measured by the difference between successive readings of the instrument m. For more accurate work, D.C. as well as A.C. is employed, as in Fig. 4b. A blocking condenser e prevents leakage of D.C. through the current meter m<1>. The D.C. performs the measuring operation by deflecting the mean axis of vibration of the part 4 towards the surface to be gauged. It is read on the meter m. The resistance c is used to control the current in the .meter m. A large condenser d prevents sudden shocks to the vibrator. A choke coil 9<1> reduces the intensity of the A.C. passing through the meter m. Further circuits to obtain more rapid results and to compensate for variations in supply voltage are described. To control the circuit of Fig. 4a automatically there is inserted in one of the A.C. leads a bridge rectifier, Fig. 6, shunted by a resistance 29 in series with the contact 28. On the opening of the contacts, the condenser 30 charges slowly and opposes the A.C. until extinction of " vibratory contact when it discharges through the resistance 29 and the cycle repeats. The reduction of the amplitude of vibration by the method just described may, in the case where unstable vibration is of excessive amplitude, be combined with a shift of the axis of vibration by D.C. The amplitude of vibration may be reduced and the instability extinguished by induced eddy currents. In this case a conducting metal strip attached to the member 4 passes between the poles of an electromagnet, the energizing current of which may be controlled by hand or relay.