Patent GB-711708-A (GB)
Title: Improvements in or relating to apparatus for computing the product or ratio of two variables
Inventor: MARTIN-HURST WILLIAM FREDERICK
IPC: G06G3/00
Filed: 1951-05-11
Abstract: 711,708. Pressure gauges; indicating apparatus. TEDDINGTON CONTROLS, Ltd. May 9, 1952 [May 11, 1951], No. 11186/51. Classes 106 (2) and 106 (4) Apparatus for computing the ratio of two variables comprises two pressure sensitive devices responsive to the two variables, each being arranged to actuate an arm in such a manner that each arm remains parallel to one of two basic related lines or axes of a graph, a follower arm carried by a shaft which is arranged to follow the point of intersection of the arms, and means for transmitting the movements of the follower to an indicating instrument The invention is described with reference to an indicator for " mach numbers" in an aircraft, this number being a function of the ratio P-S/S where P is the pressure developed due to air velocity or pitot head reading and S is the static pressure. " Mach numbers" can be plotted as a graph, where the co-ordinates represent P-S and S respectively, as straight lines passing through the origin of the co-ordinates. Fig. 1 shows a capsule a evacuated and subjected externally to static pressure, connected to a rod b guided at c so that it can move axially and is provided with a laterally extending arm d. A second pressure responsive device e is subjected to pitot head pressure internally and static pressure externally, so that the device responds to the difference between the two, i.e. P-S. This actuates a second rod f also provided with a lateral arm g. The two arms d and g intersect at right angles. Assuming lines are drawn from the various positions occupied by the point of intersection to the origin h of the co-ordinates the angles between such lines and the basic ordinate x<SP>1</SP> are functions of the various ratios between the deflections of the two pressure responsive devices, that is where # is one of such angles then tan #L (P-S)n/S, where n is any number, fraction or integer determining the law connecting the pressure P-S and S. In order to transmit variations in the angle to suitable indicating means a shaft i is arranged with its axis at the origin h of the graph and a follower arm j carried by the shaft following the point of intersection of the two arms d, g. The follower arm consists of a rod slidably mounted in a diametrical bore in the shaft one end of the rod j<SP>1</SP> engaging in the angle defined by the intersecting arms d, g. Movement of the shaft j is transmitted to a pointer O by means of a toothed quadrant m, the pointer co-operating with a scale p marked with " mach numbers." Fig. 2 shows an alternative arrangement in which the arm d is in the form of an axially extendable rod d' in a guide sleeve q carried by rod b. The arm d<SP>1</SP> merely abuts on a plane -surface on the other arm g. The other end of the arm d' abuts a plane surface of the follower arm j which actuates the rotary shaft i and through it the indicating instrument as in the form previously described. Where a computation is to be based on a graph having co-ordinates at an angle different from a right angle the intersecting rods and arms are disposed at this angle, the rods b, f being pivotally attached to the walls of the pressure responsive capsules as indicated at r.