Abstract: A detection circuit for a maximum amplitude value of a 3-phase signal wherein the three phase-signals having a phase difference of 120° from each other is converted to sampling data of digital values by an A/D converter circuit in every sampling period properly decided, and after that, when the coincidence of the values of any two phase-signals among three phase-signals is detected, the value of the remaining one phase-signal is taken as the maximum amplitude value. Thereby, an accurate maximum amplitude value can be obtained.

Abstract: A phase adjusting circuit including an input level adjuster using two detection signals having different phases and adjusting an amplitude of at least one detection signal to a predetermined level and a signal processor for signal processing including at least one of addition and subtraction on the two detection signals after level adjustment to generate a pair of output signals having a phase difference of 90 degrees or a single output signal having a phase difference of 90 degrees with respect to one of the detection signals, and a position measuring apparatus including an output level adjuster, a scaling signal generator, a detector, an A/D converter, and a memory in addition, wherein the position measuring apparatus cancels a phase error so that a signal having a phase difference of 90 degrees can be obtained.

Abstract: A position detecting apparatus for a scale measuring system executes a offset correction of the detected three-phase signals A, B and C by using the arithmetic mean (A+B+C)/3 as an offset value. Further, the apparatus executes a gain correction of the offset corrected signals by using a gain which is obtained by the calculation of a square-root of {A.sup.2 +(B-C).sup.2 /3}. Therefore, the accurate measurement is executed by this apparatus even if the gain level is changed at a turn-on of an electric source of this apparatus.

Abstract: An interpolation device for a scale arrangement receives sine wave and cosine wave signals indicative of a measuring data from the scale arrangement and calculates a DC offset value, an amplitude coefficient and an amount of a phase drift on the basis of the received signals. The interpolation device outputs a correct angle signal upon removing a DC offset, a gain level error, a gain unbalance and a phase drift from received signals. Therefore, the interpolation device realizes a mechanical structure of the scale arrangement to be simple.