GB295389A - Electrical maximum demand indicating device - Google Patents

Abstract

295,389. Siemens - Schuckertwerke Akt.-Ges. Aug. 11, 1927, [Convention date]. Special quantities, registering.- A thermal maximum demand indicator is connected during the time of peak loads by means of a frequency relay controlled from the central station by the injection of control currents. The pointer 1 is actuated by a thermostatic element 3 heated by a resistance 2. A second thermostatic element 4 renders the instrument independent of variations of room temperature. The pointer 1 actuates a non-return pointer (not shown). The heating resistance 2 is connected, in parallel with an adjustable resistance 5, to terminals 8, 12 to which are fixed contact springs 10, 11 which normally press against fixed pins 21, 22. Between the springs 10, 11 is a movable contact 13 controlled by a snap switch arm 15 which is moved into one or other of its two positions by the vibration of resonant tongues 18, 19 responsive to different frequencies. In the position shown the contact 13, which is connected to the terminal 7 of the instrument, makes contact with the spring 10 and connects the heater 2 in circuit. By the injection of a current of a frequency to which the tongue 19 is resonant, the switch arm 15 is moved over and the contact 13 makes contact, in its central position, with both springs 10, 11, short-circuiting the heater 2. In a modification the switch arm 15 controls a pawl normally engaging a ratchet-wheel on the spindle of the pointer 1, which is released only at times of peak loads. In a further modification the ratchet-wheel and pawl works directly on the thermostatic element 3. The maximum demand indicator can also be put out of action bv fixing a disengageable coupling between the thermostatic element 3. and the pointer 1, which can be supervised by a frequency relay..