Patent GB-677178-A (GB)
Title: Improvements in and relating to periodically operating controlling devices
IPC: G05B1/08
Filed: 1950-03-14
Abstract: 677,178. Mixing appliances. TROMP, K. F. March 14, 1950, No. 6368/50. Class 86 [Also in Group XXXV] In a periodically operating controlling device a weighing beam displaceable in response to the value of a magnitude to be controlled has a profiled member displaceable therewith, and feeler means are adapted to move periodically into engagement with the profiled member in points dependent upon the deflection of the weighing beam to control means for adjusting the value of said magnitude during a fraction only of each period of periodic movement. As.described the invention comprises means for controlling the density of a liquid medium which is a mixture of a relatively heavy liquid and a relatively light liquid supplied by conduits 6<1>, 6<2>, respectively, Fig. 1, into a reservoir 7, a controlled amount of the liquid mixture being byepassed into a vat 10 wherein a submerged body 2 suspended from one arm of a pivoted beam 1 changes its vertical position in response to changes 'in the density of the mixture and causes vertical displacement of a member 3 of the control mechanism carried by the opposite arm of the beam. The member 3 has a profiled surface and is movable with slight clearance across a fixed abutment 5, and a pair of feelers, 18a, 18b carried by vertical arms of bell cranks 15a, 15b are urged by springs 17a, 17b towards engagement with a profiled face on the member 3. The feelers are held away from the face of the member 3 whilst rollers 14a, 14b on the horizontal arms of the bell cranks 15a, 15b are in contact with the higher cam portion of a continuously rotating cam disc 13 and move in to engage the profiled member 3 when the low portion of the cam 13 passes the rollers. If the density of the mixture is correct the movement of the two bell cranks is arrested by engagement of the feelers 18a, 18b with a high central portion of the profiled member but should the density exceed the proper value to cause downward displacement of the profiled member 3, as shown, then the feeler 18b moves into a recessed part of the profiled member so that the horizontal arm of the bell crank 15b closes an electric contact 19b through which an electric motor 20 is driven in such a manner to actuate valve 8 to increase the amount of light liquid supplied over conduit 6<2>. Should the density fall below its proper value then conversely the profiled member is displaced upwardly and contact 19a closes to actuate the motor 20 to reduce the flow of light liquid. In the embodiment of Fig. 3 the arms 15a, 15b are connected to a sheave 27 by belts 23a, 23b the arrangement being such that movement of'one of the arms as its feeler 18a or 18b moves into a recessed part of the profiled member 3 causes tightening of the corresponding belt upon the sheave 27 and then rotates the sheave to directly operate the valve 8. The recessed surfaces of the block shown in Fig. 3 are inclined so that the degree of adjustment of the valve 8 is proportional to the degree of movement of the block 3. In the embodiment of Figs. 4 and 4a, not shown, the valve 8 is again operated directly by means of the displacement of a belt around a sheave, but the feelers are resiliently coupled to the cam operated levers and each feeler is arranged to tighten its corresponding belt when its movement is arrested by a raised portion of the profiled member. This construction is stated to reduce the noise and wear of impacting parts. In the embodiment of Figs. 2 and 2a, (not shown), the profiled member comprises a pair of blocks 3a, 3b secured in staggered relation to a pointer 21 hinged to the beam 1 by a pivot pin 22. The pointer is adapted to be urged by the action of a rotating cam 13 and bell crank lever 15 towards a pair of feelers 19a, 19b, it being so arranged that when the beam is out of the horizontal position either the block 3a engages the feeler 19a or the block 3b engages the feeler 19b to close an electric circuit to drive the valve control motor 20 in an appropriate direction. The inclined surfaces of the blocks 3a, 3b ensure that the time of operation of the motor 20 is proportional to the deflection of the beam.