Patent GB-427821-A (GB)
Title: Improvements in or relating to control instruments
IPC: G05D23/275
Filed: 1933-11-20
Abstract: 427,821. Actuation of switches. BROWN INSTRUMENT CO., Wayne Avenue, Philadelphia, U.S.A.-(Assignees of Side, F. W. ; c/o Brown Instrument Co., Wayne Avenue, Philadelphia, U.S.A.) Nov. 20, 1933, No. 32374. Convention date, March 17. [Class 38 (v)] [See also Group XXXVIII] In apparatus for measuring temperature, pressure, or other quantities, an electric switch or other control mechanism is actuated by means of two members which are relatively adjusted into different angular positions about an axis in accordance with changes in the value of the quantity measured, the members being periodically moved relatively in a direction radial to the axis, through a range of movement determined by their relative angular positions, for the purpose of adjusting the control mechanism. In the instrument shown in Figs. 1 and 4, a Bourdon tube D<3> is connected to a spindle C carrying a pointer B which moves over a record chart A. An adjustable arm E indicates the normal value of the pressure in the tube D<3>, and is connected with an arm E<1> to which is pivoted an arm F. A bell-crank lever H pivoted at A' has an arm H<1> concentric with the spindle C and passing between studs F<2>, F<3> on the arm F. The lever H is periodically moved away from the spindle C by a continuously rotating cam I, and is returned by a spring H<3>, the extent of the return movement being determined by the relative positions of the arm F and a member G, which is mounted on the spindle C and adjusted in accordance with changes in the pressure indicated by the tube D<3>. For normal values of the pressure, the return movement of the lever H is limited by the engagement of a projection F<1> on the arm F with a shoulder G<3> on the member G, while if the pressure is below the normal, the return movement is stopped at a greater distance from the spindle C by the engagement of the projection F<1> with a shoulder G<2>. For pressures above the normal, the projection F<1> escapes past the member G, and the return movement is determined by the engagement of a pin H<8> carried by the lever H with a curved slot A<10> in a fixed member A<8>. A selector member J operated by the cam I periodically adjusts the position of a mercury switch N in accordance with the different positions assumed by the lever H. The switch is carried by a frame L pivoted at A<11> to a plate A<12> formed with ratchet teeth A<14>; the latter co-operate with pawls M<1>, M<2> pivoted to arms L<1> of the frame L, in order to control the position of the switch. The switch has three positions, and in the arrangement shown in Fig. 1 is used to indicate and control the temperature of a heater O in association with the Bourdon tube D<3>, by lighting signal lamps P<1>, P<2>, P<3> and, if the temperature is above or below the normal, adjusting a valve O<1> in the appropriate direction by means of a reversible motor O<3>. In a modified construction, Fig. 8, the switch NA has two positions only, and is normally held in the open position by gravity, but is periodically moved into the closed position when required and held in that position by a latch member S having a slot co-operating with an extension on an arm L<10> carried by the switch. In this construction, the arm FA is pivoted to an arm BA carried by the spindle C, and the arm is periodically oscillated to and from the spindle C by a lever HA under the control of the cam IA and return spring HA<3>. When the pressure in the Bourdon tube D is at or above the normal value, the return movement of the lever HA is stopped by the engagement of a projection F<10> on the arm FA with a shoulder EA<1> on the member EA, but if the pressure is below the normal value, the lever HA returns to the position shown in dotted lines, and the switch is moved to the closed position. Various modifications of the clutch mechanism for maintaining the switch in its adjusted position are described, and in one arrangement a snap-over spring is used for this purpose.