GB221077A - Method of and means for taking graphs of electrical variables - Google Patents

Abstract

221,077. Baggally, W. O. A. W. Aug. 27, 1923. Combinations of instruments; potentiometers. -An apparatus for taking graphs showing the connection between electrical variables comprises a potentiometer or the like, controlling one of the variables, mechanically connected with a movable surface on which the graph is recorded by a recording-arm controlled by the second variable. The apparatus is shown applied to plotting the characteristic curves of a thermionic valve a, the potential of the grid h of which is varied, bv a potentiometer f. The contact arm f<1> of the potentiometer is rotated by clockwork, which also rotates the drum l carrying the paper on which the graph is to be made, so that one co-ordinate is proportional to the grid potential. Co-operating with the drum l is the recording- arm k<1> of a milliammeter k which mav be alternatively connected in the anode or grid circuit of the valve a by a change-over switch g. The pointer k<1> may be caused to make intermittent contact with the drum by a chopper bar &c. operated from the clockwork motor and may be provided with a thread or siphon recorder. A two-way switch. e enables either pole of the grid battery d to be earthed at will. With this switch in the left-hand position shown in full lines, the arm f is moved over the contacts of the potentiometer from the contact 2, where the maximum negative potential is applied to the grid to the contact 1 between the contacts 24, 2 where zero potential is applied to the grid. The contact 1 is earthed through a high resistance m to avoid short-circuiting the grid battery d. The switch e is then placed in its right-hand position shown in dotted lines, and the arm f<1> applies a gradually increasing positive potential to the grid, thus completing the characteristic curve. Resistances x, y, having the same value as the resistances between adjacent studs of the potentiometer, are connected between the studs 24, 2 and the positive and negative poles of the battery d. A starting-handle which removes the brake from the clockwork is interlinked with switches d<2>, b' in the grid-battery and filament circuits respectively, so that these are simultaneouslv closed. At the end of the first revolution of the potentiometer arm f<1>, the switch e is automatically moved to its right-hand position, and at the end of the second revolution the switch e is returned to its left-hand position, the switches d<2>, b<3> are opened, and the brake is put on the motor. The starting-gear may be controlled by a Bowden wire.