GB1600079A

GB1600079A - Liquid level measuring

Info

Publication number: GB1600079A
Application number: GB2546778A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-02-18
Filing date: 1978-05-31
Publication date: 1981-10-14

Description

(54) LIQUID LEVEL MEASURING (71) I, ROBERT JAMES REDDING of September House, Cox Green Lane, Maidenhead in the County of Berkshire, British Subject do hereby declare this invention to be described in the following statement: My invention is concerned with the measurement of the distance between two points and in particular with the measurement of the level of a liquid within a tank. I have found that the arrangements already described in my co-pending applications Nos. 6355, 14179 and 50046 of the year 1976 which are compounded in a complete specification filed on the 11th February 1977 (Serial No. 1523231) may be employed to overcome the problems and inaccuracy which occur in the measurement of the distance between two points as for example in measuring the distance between the level of liquid and the top of the tank by means of an ultra sonic beam.

The present practice in ultrasonic level measurements employs the transmission of a pulse by a transducer above or below the liquid level. This pulse is reflected when it meets the air liquid level. This pulse is reflected when it meets the air liquid interface and returns to the transducer. The time interval between the emission of the pulse and its receipt back depends on the velocity of sound and can be displayed in terms of the liquid level of the tank. However, the speed of sound in a medium varies with the temperature and it is necessary to measure the temperature and use this to correct the reading. If the ultrasonic beam is employed above the liquid level then changes in the atmospheric conditions above the level, e.g.

humidity and the presence of gas will be a further source of error.

According to the invention apparatus to determine the distance from a datum to a gas/liquid interfaces comprises means for generating an audio-frequency electric signal; means for generating a carrier electric signal, a frequency modulator for modulating the frequency of the carrier signal in accordance with the audio-frequency signal; a first transducer energisable by the frequency modulated carrier signal to transmit ultrasonic energy along a path through the gas from the datum to the interface; a second transducer for receiving at least part of the ultrasonic energy after transmission along said path and reflection at said interface and for producing an output electric signal in response thereto; and means for monitoring the phase relation between the audio modulation received at the second transducer and that transmitted by the first transducer, to give an indication of the said distance. The detection of changes in the atmosphere is the purpose of the invention described above and is performed by a plurality of transducers. Instead of a straight path in air a pair of transducers can be located at the top of a tank facing a liquid level below them. Thus the ultrasonic wave transmitted by one will received by the other by reflection from the liquid surface and the phased locked loop frequency will be changed as the level moves up and down.

The system may thus be used to measure the level of liquid. Further by the use of a plurality of such transducers we can obtain a level of indication independent of the changes of the speed of sound in the transmission path.

Thus if one pair of transducers is situated a known distance further from the liquid than another pair then the two frequency readings can be computed to give a level measurement independent of changes in the transmission path (be it liquid or gas). It is in fact possible to use a single transmitter and two receivers spaced a fixed distance apart along the plane of measurements. The loop locks on one transducer whilst the second receiving transducer notes the phase relationship corresponding to the known distance from which the total distance can be computed by known electronic means and displayed as a level measurement. Thus just as we can show the change in gas contained in an unspecified distance in air we can inversely show the distance from a fixed point to a movable one such as a liquid level without confusion from changes in the intervening space.

Although described as a level at which reflection occurs the reflection can, of course, be enhanced where necessary by a solid object floating on a liquid level or other interface and the reflection can be enhanced by suitable geometry for example a parabolic reflection or channel guide system may be used to enhance the ultrasonic transmission as described in the earlier application.

WHAT I CLAIM IS: 1. Apparatus to determine the distance from a datum to a gas/liquid interface comprising means for generating an audiofrequency electric signal; means for generating a carrier electric signal, a frequency modulator for modulating the frequency of the carrier signal in accordance with the audio-frequency signal; a first transducer energisabeby the frequency modulated carrier signal to transmit ultrasonic energy along a path through the gas from the datum to the interface; a second transducer for receiving at least part of the ultrasonic energy after transmission along the said path and reflection at said interface and for producing an output electric signal in response thereto; and means for monitoring the phase relation between the audio modulation received at the second transducer and that transmitted by the first transducer, to give an indication of the said distance.

2. Apparatus as claimed in Claim 1 wherein an additional third transducer spaced a known distance from the first and second transducers along the path to be indicated is used as a reference on computation of the distance.

3. Apparatus to determine the distance from a datum to a gas/liquid interface substantially as herein described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. reflection occurs the reflection can, of course, be enhanced where necessary by a solid object floating on a liquid level or other interface and the reflection can be enhanced by suitable geometry for example a parabolic reflection or channel guide system may be used to enhance the ultrasonic transmission as described in the earlier application. WHAT I CLAIM IS:

1. Apparatus to determine the distance from a datum to a gas/liquid interface comprising means for generating an audiofrequency electric signal; means for generating a carrier electric signal, a frequency modulator for modulating the frequency of the carrier signal in accordance with the audio-frequency signal; a first transducer energisabeby the frequency modulated carrier signal to transmit ultrasonic energy along a path through the gas from the datum to the interface; a second transducer for receiving at least part of the ultrasonic energy after transmission along the said path and reflection at said interface and for producing an output electric signal in response thereto; and means for monitoring the phase relation between the audio modulation received at the second transducer and that transmitted by the first transducer, to give an indication of the said distance.