Two-transducer Doppler flowmeter with swept oscillator

A doppler flowmeter measuring system for measuring the flow of a fluid in a conduit comprising:

• first transducer means connected to a first portion of said conduit and operable for injecting ultrasonic energy into said fluid;
• second transducer means separate from said first transducer means and connected to a second portion of said conduit and operable for receiving ultrasonic energy injected into said fluid by said first transducer means and reflected by energy reflecting objects in said fluid;
• a high frequency generator connected to said first transducer means for causing said first transducer means to inject ultrasonic energy into said fluid with a wave form at least generally following the wave form of the output of said high frequency generator;
• means coupling a portion of the output ultrasonic energy of said first transducer means directly to said second transducer means, whereby the output of said second transducer means is a wave form which is the summation of the wave form of ultrasonic energy received directly from said first transducer means and the ultrasonic energy reflected from reflecting objects in said fluid;
• amplitude demodulation means connected to said second transducer means for demodulating the beat frequency content in the output of said second transducer means and for producing an output signal related to said beat frequency;
• said wave form of ultrasonic energy injected into said fluid by said first transducer means containing a relatively low frequency cyclic dither;
• said relatively low frequency cyclic dither having a cyclic frequency which is relatively high in comparison to the highest beat frequency which is to be produced by said measuring system;
• said high frequency generator having a continuous output wave form of constant amplitude in a frequency range of from 600 kilohertz to 1500 kilohertz;
• said frequency dither superimposed on said continuous wave form at a frequency which varies continuously in a range up to about 25% of the frequency of said continuous output wave form;
• said frequency dither having a repetition rate of greater than about 10 times the highest expected beat frequency to be measured by said system.

A flowmeter using doppler measurement techniques and employing a transmitting transducer and a receiving transducer which are coupled to the exterior of a fluid carrying conduit;

• said receiving transducer being located to receive ultrasonic energy from said transmitting transducer through the wall of said conduit and to receive ultrasonic energy reflected from particles in the fluid carried by said conduit;
• said receiving transducer connected to demodulating and indicating circuit means for measuring the beat frequency output of said receiving transducer and displaying said output as a function of the flow velocity of the fluid within said conduit;
• and a transmitter oscillator means connected to said transmitting transducer, said transmitter oscillator means having a continuous wave output which has a superimposed dither frequency which varies over a given cycle at a given cycle rate, whereby the effects of standing waves on the flow measurement are eliminated;
• said transmitter oscillator means having a continuous output wave form of constant amplitude in a frequency range of from 600 kilohertz to 1500 kilohertz;
• said superimposed dither frequency on said continuous wave form having a frequency which varies continuously in a range up to about 25% of the frequency of said continuous output wave form;
• said dither frequency having a repetition rate of greater than about 10 times the highest expected beat frequency to be measured by said system.