BERUEHRUNGSFREIE LAENGENMESSEINRICHTUNG

1458828 Photo-electric dimension measurement DAIDO SEIKO KK 19 Dec 1973 [27 Dec 1972] 59320/73 Heading G1A To determine a linear dimension of a body such as a moving steel rod 3, Fig. 1, it is illuminated with a collimated light beam and the shadow so formed is projected on to a line of photo-detectors 9 by a lens 4 and slit 5. The number of detectors in the shadow at any instant is a measure of the dimension of the body, and is averaged over a period of time to give a mean value of the dimension. The line of detectors need not be continuous, and those detectors in the central portion of the shadow can be omitted. Fig. 3 shows a circuit which counts the number of detectors in shadow at a given time. It also takes an average of the count over a period of time, so that the accuracy of the system increases; this increase is obtained only if the body is vibrated, either deliberately or as a result of its exit from a drawing or machining process. The detectors 9 are connected to amplifier 10, AND gates 11, one bit registers 12, sequential pulse generator 17, AND gates 14, OR gate 15 and counter 16. When generator 13 is pulsed the detector signals enter the registers, and then a sequence of pulses from generator 17 passes the register contents to the OR gate 15 and counter 16. A further generator 19 emits a pulse, say once per second, so that the average count over one second is also made, at register 20, and displayed at 21. If two Schmitt triggers are connected to each detector, and have thresholds at one half the maximum detector output and at the maximum detector output respectively, the sensitivity of the measuring device is effectively doubled; alternatively the total number of detectors can be halved while the overall sensitivity is maintained. Further triggers can be used to increase the sensitivity even more.