GB464867A - Protective means for electrical measuring instruments - Google Patents

Abstract

464,867. Automatic circuit-breakers ; protecting testing-instruments. MACADIE, H. S., and AUTOMATIC COIL WINDER & ELECTRICAL EQUIPMENT CO., Ltd. Sept. 25, 1935, No. 26571. [Class 38 (v)] [Also in Group XXXVI] A protective device for an electrical measuring-instrument comprises a spring-loaded switch which is caused to break the circuit or shortcircuit the instrument when a moving part of the instrument accelerates too quickly or reaches the limit of its movement in either direction. In the arrangement shown, the pointer 5 is carried by a slightly flexible metal strip 4 pivoted at 3 to a part 1 carried by the moving coil 2 of the instrument. The part 1 has an extension 11 against which the pointer is normally pressed by a spring 6. The strip 4 is formed with a pawl 7 which is normally out of engagement with a ratchet 12<3> carried by a member 12, Fig. 3, pivoted at 13 to the magnetic concentrator 14. The member 12 is formed with recesses 121, 122 engaging lugs 94, 9<5> on a member 9, Fig. 4, mounted so as to be capable of longitudinal movement in bridge pieces 10<1>, 10<2> connecting the polepieces 11<1>, 11<2> of the instrument. If the coil 2 moves or accelerates too rapidly, the inertia of the pointer 5 causes the pawl 7 to engage the ratchet 123 and rotate the member 12, whereupon the member 9 is depressed, and an arm 9<3> carrying an abutment 9<6> lowers a rod 15 guided at 151 and trips a switch to the open position. The switch comprises a bridge piece 17 carried by a rod 18 provided with a reset button 20, by means of which the bridge piece can be moved into engagement with fixed contact arms 16, 16<1>. A pivoted arm 22 under the action of a spring 23 engages a conical recess 24 in the rod 18 and holds this in the closed position, the free end of the arm 22 being held by a catch 25 connected to the rod 15. When the rod 15 is depressed, the catch is released, and the switch opens under the action of a spring 21. Rotational displacement of the bridge piece 17 is prevented by a guide 27 having a recess which engages a post 28. At the limits of its movement in either direction, the coil 2 engages the portion 124 or 12<5> of the member 12 and rotates the latter to open the switch.