Patent GB-364660-A (GB)
Title: Improvements in or relating to relay devices for controlling regulating, recording or similar apparatus
IPC: G05B1/08
Filed: 1930-09-29
Abstract: 364,660. Thermostats. JAMES, R. W., 11, Queen Victoria, Street, London.-(Brown Instrument Co. ; 4433, Wayne Avenue, Philadelphia, U.S.A.) Sept. 29, 1930, No. 29093. [Class 64 (ii).] In a measuring instrument which controls a relay mechanism for effecting the control of recording or signalling apparatus or for regulating quantities such as the heat supply to a furnace the relay mechanism is adapted to set a secondary pointer selectively in a position corresponding to the position of the instrument pointer and thereby effect a control operation which takes place after the instrument pointer is again freed to take up a fresh position. As shown in Fig. 1, a power-driven shaft F allows through the action of the cam e, the member C to fall periodically into contact with the instrument pointer B<1>. The member C has a stepped surface C<3> and the extent of fall determines, according to the deflection of the pointer B<1>, the position of a secondary member H which co-operates with the switchoperating members K, KA of a reversible motor 0. The shaft F also carries a cam g which controls levers G, EA. Just after projection E<1> on lever E drops into depression e<1> to lower the member C, the projection G<1> falls into depression g<1> of cam g to allow release of lever G which lowers the pivoted secondary member H the tooth H<1> of which remains locked by a rack P on a pivoted bar I until a projection I<2> engages projection E<3> on lever E which is in the raised position. The lever H is then freed and takes up a position determined by the member C through the rod C<1>. Following the dropping of projection G<1> projection E<5> on lever EA falls into notch g<1> and weighted member E<6> falls to operate lever E and thus raise the member C out of contact with the pointer B<1> to free the latter for further deflection. When the lever E is operated in this manner, projection E<3> is lowered and the secondary member H<1> is locked in its new position by the bar I. Subsequently to these operations the lever G is again raised by the cam g and depending upon the setting of the member H one or other of the pivoted levers K, KA is operated to a variable extent depending upon the deflection of the pointer B<1>. Each lever has a stepped surface K<1> and the movement given to either lever when one of its steps is engaged by the tooth H<1> is greater or less according as the engaged step is at a greater or less distance from the neutral position of the tooth. The levers K, KA operate pivoted switch levers L, LA through spring toggles M, MA to control the reversible polyphase motor 0. The duration of each energization of the motor 0 depends on the angular position of the member H and therefore on the deflection of the pointer B<1>. The motor may be employed to adjust a potentiometer or Wheatstone bridge controlling the meter B or perform a relay function in anv control system of which the meter forms a part, such as controlling the heat supply to a furnace. In a modification the levers K, KA control a reversible ratchet mechanism for adjusting a rheostat. Fig. 5 shows a system for comparing the values of resistances R<1>, R<2> which may be located in the test and standard gas cells of a gas analysis apparatus. The resistances are connected in a Wheatstone bridge and the relay mechanism is provided to facilitate the maintenance of the energizing current of the bridge at its proper value. A lever T pivoted to lever E carries a contact Y which moves into engagement with contact W when a projection T<1> falls into the depression e<1> of the cam e. The resistance r in the bridge is thus connected in the circuit of the instrument B and the relay mechanism is operated to adjust the rheostat P and restore the energizing current to normal in the event of any variation. When the cam moves the lever T into engagement with the contact U the normal bridge connection is restored, the slider S together with arms R3r, R<4> being included. In a modification the switch Y, U, W is replaced by a double-pole switch which is adapted to switch into circuit a resistance r which is independent of the bridge.