| 摘要 |
Apparatus for monitoring the state of a first circuit (19) by means of a second circuit (29) has an inductive coupling (23) linking the circuits across a gap (32). The second circuit embodies an oscillator (27) producing primary oscillations in that circuit and, through the coupling, secondary oscillations in the first circuit (19). If the state of the first circuit (19) is changed as by opening or closing of contacts (17,18), the resulting change in the impedance of the first circuit results in a change in the frequency of the primary and secondary oscillations. The second circuit (29) is connected to a detector (35) producing a signal (37AI) when the frequency changes. Instead of an inductive coupling, a capacitative coupling may be used. The apparatus is described as applied to a machine for measuring length. The first circuit (19) is embodied in a probe (12) whereby the machine contacts a workpiece to be measured. The first circuit is opened by such contact. The second circuit (29) is embodied in a head on which the probe is releasably mounted. Since the first circuit (19) is a passive one, the probe does not need an independent power supply, and a power supply in the head serves any one such probe that may be mounted on the head.
|
