Patent GB-288186-A (GB)
Title: Improvements in and relating to electric measuring instruments
IPC: G01R23/02
Filed: 1928-04-02
Abstract: 288,186. British Thomson-Houston Co., Ltd., (Assignees of Rich, T. A.). April 2, 1927, [Convention date]. Frequency, inductances, capacities, and resistances, measuring.-A frequency meter has cooperating stationary and movable members on one of which opposing coils producing a resultant flux are mounted, a winding on the other member for producing a flux which co-operates with this resultant to produce a deflecting torque, and means for producing an opposing torque. One construction is shown in Fig. 1, the connections being shown in Fig. 3. A stationary field winding 10 is divided into two parts connected in series. The moving element comprises a shaft 11 carrying a pointer 12, a pair of coils 13, 14, and a magnetic vane 15 fixed to the shaft in the plane of the coils 13, 14. The connections to the moving coils are carried through flexible conductors 16, 17, 18 exerting negligible torque. In circuit with the coils 13, 14 are means for varying the current distribution between the coils as the frequency varies. As shown, an inductance 19 is connected in series with the coil 13, and a resistance 20 in series with the coil 14. The values of the inductance 19 and resistance 20 are so chosen that the resultant flux of the coils 13, 14 is zero at the central point of the scale. At a higher frequency less current flows through the inductance 19, that through the resistance 20 being unaltered, consequently a torque is produced which turns the moving coils to a new position against the restoring torque due to the vane 15. On decrease of frequency a greater current flows through the inductance 19, producing a deflection in the opposite direction. The scale distribution may be altered by changing the angle between the coils 13, 14 and the vane 15. The coils 13, 14 may be stationary and the coils 10 may be carried by the moving part, combinations of inductance and capacity being connected in circuit with the coils 13, 14. For adjusting the length of the scale, a variable resistance may be connected between the junction of the coils 13, 14 and the junction of the inductance 19 and resistance 20, or, when the coils 10 form the moving system, a portion of the armature current may be shunted through a resistance. The field winding may be separately excited through a limiting resistance. A doublerange instrument is shown in Fig. 7, in which a resistance 27<1> is inserted in shunt to the winding 10 by closing a switch 29. Another doublerange instrument is shown in Fig. 8 in which a switch 29<1>, when turned to the position shown in dotted lines, cuts out the inductance 22 and condenser 24 and replaces them by a resistance 30, at the same time cutting out, the condenser 25 and part of the inductance 23. Fig. 9 shows a construction in which the stationary coils 32, 33 are differentially connected in parallel circuits containing an induct.. ance 19 and resistance 20. The movable coil 34 is connected in series with these parallel circuits across the frequency source to be measured. A stationary magnetic vane 35 is arranged parallel to the coils 32, 33. The magnetic vane in any of the constructions may be replaced by another coil 36, Fig. 13, at right-angles to the armature coil 10<1>. On a circuit of constant frequency the instrument may be calibrated to measure inductance, capacity, or resistance, which is inserted in place of one of the elements 19, 20.