GB575594A - Improvements in or relating to frequency meters - Google Patents

Abstract

575,594. Frequency measurements. COMPAGNIA PARA LA FABRICACION DE CONTADORES Y MATERIAL INDUSTRIAL SOC. ANON., and VITEAU, P. March 29, 1944, No. 5793. [Class 37] A frequency meter has two ranges of measurement, one according to a double resonance connection and another according to an antiresonant connection, the same frequencysensitive elements being employed in both connections by grouping the condensers and inductances of the first connection in parallel to obtain the condenser and inductance of the second. Two fixed coils 13, 13<1> co-operate with a movable system comprising a wound double frame 15 and an iron bar 16, both fixed on the spindle 17. Condensers 11, 11<1> and inductances 12, 12<1> are connected as shown to a multiple switch 34 operated by an electromagnet 35. The scale 33 of the instrument has a lower scale for high-sensitivity measurement graduated from 49.5 to 50.5 cycles per second and an upper scale for lower-sensitivity measurement graduated from 35.5 to 49.5 cycles per second. The deflection of the movable system is reversed on change of sensitivity so that the two scales are graduated in opposite directions and have a common limit of 49.5. In the position shown the frequency has fallen to 49.5 and the pointer 36 has closed contacts 37 so that the electromagnet 35 has changed over the switch 34 from the high-sensitivity to the low-sensitivity position shown. A maintenance relay 38 is also excited and a pilot lamp 39 lights up. In this position of the switch 34 the condensers 11, 11<1> are in parallel with one another and in series with the coil 13 and the movable coil 15 across the mains U. The inductances 12, 12<1> are in parallel and in series with the coil 13<1> and movable coil 15 across the mains. The closed circuit 13, 13<1>, 12, 12<1>. 11, 11<1> is tuned to the Nominal frequency of the apparatus. With the switch 34 in the other position the coil 13 is in series with the inductance 12 and condenser 11 and is tuned to a lower frequency than the nominal. The coil 13<1> is in series with the inductance 121 and condenser 11<1> and is tuned to a higher frequency than the nominal. The moving coil 15 is traversed by the sum of the currents in these two circuits. When the frequency resumes its normal value of 50 cycles per second, the return to the range 49.5-50.5 is obtained by operating a switch 40 in order to break the circuit of the maintenance relay 38. Alternatively the range-changing may be automatic in both directions.