GB1191085A - Digital Measurement Apparatus - Google Patents

Abstract

1,191,085. Counting apparatus; selective signalling. GENERAL ELECTRIC CO. 14 Feb., 1969 [29 Feb., 1968 (3)], No. 8263/69. Headings G4A and G4H. In a measuring system in which pulses are produced each representing a known increment of the variable being measured, for example pulses from an interferometer where each pulse represents a displacement of 3À1142697 x l0<SP>-6</SP> inches, the pulses are counted and means are provided for periodically subtracting unity from the highest non-zero denomination of the counter and for accumulating a corresponding multiple of the incremental value of each pulse. In this way the total accumulated does not lag far behind the total number of pulses produced, and it represents the value of the variable being measured in more convenient units. Means may be provided to modify the incremental value of each pulse in accordance with the existing ambient conditions. The system may form part of a rectroactive machine tool control loop (Fig. 6, not shown). As described add and subtract pulses UPL, DNL, Fig. 2, from an interferometer are passed, via a sign stage 18 and leads UPI, DNI, to a reversible, binary-coded-decimal gated counter, Figs. 3, 4, the sign stage 18, Fig. 2, functioning either to connect lead UPL to UPI and DNL to KNI if a sign trigger 72 is on indicating a positive sign, or to connect lead UP1 to DN1 and lead DNL to UP1 if the sign trigger is off. The state of the sign trigger is determined by the first pulse from the interferometer that occurs after the counter reaches zero, which is detected by a gate 65. This pulse also always passes via a gate 73 to the add lead UP1. The contents of the counter are examined by a recognition circuit 15, Fig. 2, which, when an arithmetic control unit (not described) is ready, and when a buffer store is ready, this being evidenced by the presence of signals RECO, PCR, produces a signal #CORR 1 or #CORR 10 or #CORR 100 indicating the highest non-zero denomination of the counter. This signal then causes a one to be entered into a corresponding stage of a buffer store (Fig. 5, not shown) and a one to be subtracted from the corresponding denomination of the counter. Under control of the buffer store, a corresponding multiple (1, 10 or 100) of the incremental value of each pulse from the interferometer is then transferred (by means not described) to an accumulator. This process continues until the counter is empty.