Instrument measuring weight per unit length or moisture of running fibrous strand before e.g. carding, combing or spooling, is based on microwave resonance

摘要

The instrument includes a microwave oscillator (50) with an active amplifier (27, 28) and a feedback network having a frequency-determining resonance circuit. This circuit is equivalent to an LC-oscillator with theoretical components R1, C1 and L1. The microwave resonator (21) is the embodiment of this circuit. It follows that the microwave oscillator frequency, is the frequency at which the resonator (21) is resonant. A frequency measurement circuit (31) produces a frequency signal (FS) which corresponds with the frequency of the microwave oscillator. FS is analog or digital. The active amplifier (27, 28) has linear automatic gain control or AGC circuitry (28), in which an amplitude signal (ASS) is used to hold the signal level constant. A feedback control circuit keeps the input signal (ES) of the active amplifier at constant amplitude. Corresponding circuitry variants are also described. The oscillator design, keeps amplification within the linear range. The measurement chamber (22) of the resonator is coupled (25) via a transformer (26) with the input and output signals of the active amplifier. The microwave oscillator is designed as a three-point oscillator. It is a Meissner oscillator. The amplitude detector (32) includes rectification and a differential amplifier for comparison with a reference amplifier. A directional coupler may be used to extract two phase components in quadrature. These are processed to produce a proportional signal which is compared with a given reference signal. The instrument precedes a machine preparing fibers for spinning, e.g. a card, comb, spinning or winding machine.