| 摘要 |
<p>The invention concerns a method and an apparatus for measuring the level of a material with microwave signals. The apparatus consists of a signal processing unit (10) and a transmitter unit (1) of known type. The transmitter unit produces a measuring signal having a frequency (fm) corresponding to the distance (H) to be measured and a reference signal having a frequency (f,) corresponding to an accurately known length (L). In the signal processing unit (10) the reference signal is multiplied by a selectable number (AQ) which is proportional to the quotient of an assumed value for the distance divided by the known length (L), after which the frequency is divided by a fixed number (Z) so that the frequency of the signal after multiplication and division becomes equal to the expected frequency of the measuring signal. Thereafter the control signal thus produced is mixed with the measuring signal, for determination of the phase difference between them which is sampled in each of a succession of regular sampling intervals, and the change in phase difference through the successive sampling intervals is calculated for determining a correction term for the assumed distance.</p> |
