Liquid level measurement

Claim 1

I. A method of determining the level of liquid in a storage tank which comprises the steps of transmitting a series of sonic pulses through the liquid from a transmitter positioned at the bottom of the tank so that such pulses are on the one hand at least partially reflected from the surface of the liquid, and on the other hand at least partially reflected from a reflector positioned at a reference level above the transmitter whilst the level of the liquid is above said reflector, detecting such reflected pulses and measuring the time interval between a transmitted pulse and a first corresponding reflected pulse, determining whether any further corresponding reflected pulse is received from the same transmitted pulse in order to determine whether said first reflected pulse derives from said reflector or from the surface of the liquid, storing the value of the measured time interval for the first reflected pulse if a second reflected pulse is detected, at least on the first occasion that a reflected pulse is received in a series of measurements, to provide a reference value, and deriving from any second reflected pulse where such pulse is received from a given transmitted pulse, or from any first reflected pulse when no second reflected pulse is received from a given transmitted pulse, an output signal corresponding to the level of liquid in the tank.

Claim 2

A method according to Claim I additionally including the step of transmitting said series of sonic pulses so that such pulses are also at least partially reflected from an additional reflector positioned at a second reference level near to the bottom of the tank, detecting the additional reflected pulses produced by said additional reflector and measuring the time interval between a transmitted pulse and a corresponding additional reflected pulse, comparing the ratio of the measured time interval for such additional pulse to the known distance between said transmitter and said additional reflector with the ratio of the measured time interval for a reflected pulse from said first mentioned reflector to the known distance between said transmitter and said first mentioned reflector, and generating an alarm signal if the two ratios are significantly different.

Claim 3

A method of determining the level of liquid in a storage tank which comprises the steps of transmitting a series of sonic pulses through the liquid from transmitter means positioned at or adjacent to the bottom of the tank so that transmitted pulses are reflected at least partially from the surface of the liquid, at least partially from a high level reflector whilst the level of the liquid is above said reflector which is spaced above the transmitter means by a first reference distance, and at least partially from a low level reflector whilst the level of the liquid is above said reflector which is positioned at a second reference distance above the transmitter means, detecting such reflected pulses and measuring the time interval between transmitted pulses and corresponding reflected pulses, and whilst reflected pulses are being received from both of said reflectors, at least on the first occasion that both such reflected pulses are received in a series of measurements, comparing the ratio of the measured time interval for return of a reflected pulse from said first reflector to said first reference distance with the ratio of the measured time interval for receipt of a reflected pulse from said second reflector to said second reference distance, and generating an alarm signal if the two ratios are significantly different, and deriving an output signal corresponding to the level of liquid in the tank by comparing the measured time interval for return of a reflected pulse from the surface of the liquid with the measured time interval for return of a reflected pulse from at least one of said reflectors.

Claim 4

A method of monitoring the level or quantity of liquid in a storage tank during intermittent or continuous discharge thereof, comprising the steps of:- (a) transmitting at least one reference pulse of sonic energy from a transducer positioned helow the surface of the liquid towards a reference reflector positioned below the maximum permissible level of liquid in the tank at a predetermined spacing from said transducer,, so as at least partially to reflect said reference pulse to detector means, and measuring the time interval between transmission of said reference pulse and receipt by said detector means of a reflected pulse from said reflector to provide a reference value; (b) detecting the arrival at the same or different detector means of a further reflected pulse from the same or a different reference pulse from the surface of the liquid at its initial level, measuring the time interval between transmission of the reference pulse and receipt of the corresponding surface reflection pulse at the detector means to provide an initial value representive of the initial liquid level or quantity by reference to said reference value; and (c) thereafter transmitting a series of measurement pulses so as to be reflected at least from the surface of the liquid and measuring the time interval between the transmission of each such pulse and receipt of the corresponding liquid surface reflection pulse to provide a measurement value representative of the subsequent liquid level or quantity.

Claim 5

A method of monitoring the level or quantity of liquid in a storage tank during intermittent or continuous discharge thereof, comprising the steps of:- (a) transmitting at least one reference pulse of sonic energy from a transducer positioned below the surface of the liquid towards a first reference reflector positioned below the maximum permissible level of liquid in the tank at a predetermined first spacing from said transducer, so as at least partially to reflect such reference pulse to detector means, and measuring the time interval between transmission of such reference pulse and receipt by said detector means of a reflected pulse from said first reflector to provide a first reference value; (b) transmitting at least one reference pulse of sonic energy from a transducer positioned below the surface of the liquid towards a second reference reflector positioned adjacent to the bottom of the tank at a predetermined second spacing from said transducer, so as at least partially to reflect such reference pulse to detector means, and measuring the time interval between transmission of such reference pulse and receipt by said detector means of a reflected pulse from said second reflector to provide a second reference value; (c) detecting the arrival at the same, or different detector means of a further reflected pulse which derives from the same or a different reference pulse from the same or a different transducer after reflection from the surface of the liquid at its initial level, measuring the time interval between transmission of such reference pulse and receipt of the corresponding surface reflection pulse at the detector means to provide an initial value representative of the initial liquid level or quantity by reference to either or both of said reference values; (d) comparing the ratio of such first reference value to said first spacing with the ratio of such second reference value to said second spacing and generating an alarm signal if the two ratios are significantly different; and (e) thereafter transmitting a series of measurement pulses so as to be reflected at least from the surface of the liquid and measuring the time interval between the transmission of each such pulse and receipt of the corresponding liquid surface reflection pulse to provide a measurement value dependant on the subsequent liquid level and deriving an output signal representative of the liquid level or quantity by comparing said measurement value with said first and/or said second reference values or subsequently determined corresponding reference values.

Claim 6

A method of determining the level of liquid in a storage tank which comprises the steps of transmitting a series of sonic pulses through the liquid from transmitter means positioned at or adjacent to the bottom of the tank so that transmitted pulses are reflected at least partially from the surface of the liquid, transmitting a series of sonic pulses laterally through the liquid from the same or different transmitter means and positioned at or adjacent to the bottom of the tank so that such pulses are at least partially reflected from a reference reflector positioned at a reference distance from the transmitter means, detecting such reflected pulses and measuring the time interval between transmitted pulses and corresponding reflected pulses, and deriving an output signal corresponding to the level of liquid in the tank by comparing the measured time interval for return of a reflected pulse from the surface of the liquid with the measured time interval for return of a reflected pulse from said reference reflector.

Claim 7

A method according to any one of the preceding claims including the steps of determining the temperature of the liquid during the measurement and applying any required compensation factor if the observed temperature changes between the establishment of the reference value and any subsequent measurement in the same series of measurements.

Claim 8

A method according to any one of the preceding claims including the step of comparing the observed reference value with a stored datum value corresponding to the calculated time interval for a reflected pulse from said reflector for a specified liquid at the measured temperature and generating a warning signal in response to any significant discrepancy between the observed reference value and the datum value.

Claim 9

A method according to Claims 7 and 8 wherein the observed reference value and the measured temperature are compared with stored values corresponding to the density of selected liquids over a predetermined range of temperatures to provide an indication of the density of the liquid in the tank and/or its nature.

Claim 10

A method according to any one of the preceding claims wherein the output signal is used to derive an indication of the volume or mass of liquid corresponding to the measured depth.