Title of Invention

AN ULTRASONIC LIQUID LEVEL SENSOR

Abstract An ultrasonic liquid level sensor is provided which comprises a sensor head having a sealed top at one end and a sensing gap along part of the length of the sensor head, a piezoelectric disc transmitter and piezoelectric disc receivers provided on each side of the said sensing gap with connecting leads from the piezoelectric disc transmitter and the piezoelectric disc receiver. The other end of the sensor head is sealingly connected to a hollow stem provided with a sensor cap with an electrical connector for taking out the connections from the piezoelectric disc transmitter and piezoelectric disc receiver to an external circuit.
Full Text The invention relates to an ultrasonic liquid level sensor with very high reliability. Ultrasonic liquid level sensor according to the invention is particularly useful in applications which require extreme accuracy and reliability such as sensing propellant level in launch vehicle.
Ultrasonic liquid level sensors known in the art have questionable reliability due to the type of materials used in their manufacture, compatibility with propellants, limitations to the operating pressure, the operating temperature and the vibration with-standing capability. The invention provides an ultrasonic liquid level sensor which is relatively light and having a repeatability of sensing level better than ±.0. 1mm and an accuracy of better than +0.1mm. It can operate at a low temperature upto 0°C and at random vibration levels upto 20 gms at 20Hz to 2KH2. It is also compatible with most of the propellants used in space craft.
Thus the invention provides an ultrasonic liquid level sensor comprising a sensor head having a sealed top at one end and a sensing gap along part of the length of the sensor head, a piezoelectric disc transmitter and a piezoelectric disc receiver being provided on each side of the said sensing gap with connecting leads from the piezoelectric disc transmitter and the piezoelectric disc receiver, the other end of the sensor head being sealingly connected to a hollow stem provided with a sensor cap with an electrical connector for taking out the connections from the piezoelectric disc transmitter and piezoelectric disc receiver to an external circuit.

The ultrasonic liquid level sensor according to the invention will now be described in detail with reference to the accompanying drawing:
Fig. 1 shows the ultrasonic liquid level sensor according to the invention.
Refering to Fig. 1, the ultrasonic liquid level sensor conprises a sensor head (2> having a sealed top (1). The top is sealed to the body of the sensor head preferably by electron bean welding (EBW> to obtain a high quality hermetic sealing. A piezoelectric transmitter disc (T> and a piezoelectric receiver disc (R> are provided on the sides of a sensing gap are connected through connecting leads (7. 8) preferably through a low inductance of about 47 micro henries to a connector (5) in a sensor cap (4) sealingly connected to a hollow stem (3). The hollow stem (3> is sealingly connected to the sensor head (2). The sealed connections between the hollow stem (3> and the sensor head (2> and that between the stem and the sensor cap (4) are preferably electron beam welded are preferably teflon coated wires to provide better insulation. The

sensor head is preferably filled with an epoxy (6> so that the transmitter disc , the sealed top The method of making the ultrasonic liquid level sensor according to the invention comprises the following steps. A sensing head (2) with a sealed top (1) is made of non-magnetic stainless steel. The piezoelectric transmitter disc (T) and the piezoelectric receiver disc with connecting leads (7, 8) are mounted on either side of the sensing gap (G> of the sensor head and they are encapsulated with an epoxy by filling the sensor head with a mixture of epoxy resin and hardner and allowing the resin to cure. The sensor head (2> is sealingly connected to the stem (3) and the sensor cap (5) is sealingly connected to the stem (3) after the lead wires (7, 8> are connected to the electrical connector (5) in the cap (4),
The piezoelectric disc transmitter and piezoelectric are preferably made of high sensitivity, ferroelectrically soft lead zirconate titanate piezoelectric material. They provide excellent time stability and relatively high electrical resistivity at high temperatures.

The nitrasonic liquid level sensor is used for sensing level by applying an ultrasonic voltage source to the terminals connecting to the disc to transmitter (T) and measuring the output at the terminals connecting the disc receiver (R). The frequency of the applied source is preferably between IMHz to 1.2MHz. The output at the terminals of the receiver will be present only if the sensing gap is completely filled with the liquid. Even an air gap of 0.1 mm will make the receiver output zero. Thus the liquid level sensor according to the invention can be used for very accurate liquid level controls. The liquid level controllers are tested for satisfactory operation at temperatures from 0°C to 70*^, vibration levels upto 20 gms at 20Hz to 2KHz random and at pressures upto 20 bars. These liquid level controllers can be made with a weight of less than 250 gms.



WE CLAIM :
1 . An ultrasonic liquid level sensor comprising a sensor head (2) having a sealed top (1) at one end and a sensing gap (G) along part of the length of the sensor head (2), a piezoelectric disc transmitter (T) and a piezoelectric disc receiver (R) being provided on each side of the said sensing gap (G) with connecting leads (7,8) from the piezoelectric disc transmitter (T> and the piezoelectric disc receiver (R>, the other end of the sensor head (2) being sealingly connected to a hollow stem (3) provided with a sensor cap (4) with an electrical connector (5) for taking out the connections from the piezoelectric disc transmitter (T) and piezoelectric disc receiver (B) to an external circuit.
2. The ultrasonic liquid level sensor as claimed in claim 1, wherein the piezoelectric disc transmitter (T) and piezoelectric disc receiver (R> are encapsulated in the sensor head (2).
3. The ultrasonic liquid level sensor as claimed in claim 2, wherein the encapsulation is an epoxy encapsulation.
4. The ultrasonic liquid level sensor as claimed in any one of
the previous claims, wherein the piezoelectric disc transmitter
(T) and piezoelectric disc receiver (R) are identical lead
zirconate titanic piezoelectric transducers.

5, The ultrasonic liquid level sensor as claimed in any one of the previous clains, wherein the connecting leads (7, 8> are connected to the disc transmitter (T> and disc receiver (R) through an inductance of about 4? micro henries.
8. The ultrasonic liquid level sensor as claimed in any one of the previous claims, wherein the connecting leads (7, 8) are teflon coated conducting wires.
7. The ultrasonic liquid level sensor as claimed in any one of
the previous claims, wherein the sealed top (1) of the sensor
head (2). the connection between the sensor head (2) and hollow
stem (3) and the connection of the sensor cap (4> with the hollow
stem (3) are electron beam welded (EBW) hermetic seals.
8. An ultrasonic liquid level sensor, substantially as
hereinabove described and illustrated with reference to the
accompanying drawings.

Documents:

0742-mas-1999 abstract.pdf

0742-mas-1999 claims-duplicate.pdf

0742-mas-1999 claims.pdf

0742-mas-1999 correspondence-others.pdf

0742-mas-1999 correspondence-po.pdf

0742-mas-1999 description(complete)-duplicate.pdf

0742-mas-1999 description(complete).pdf

0742-mas-1999 drawings granted.pdf

0742-mas-1999 drawings.pdf

0742-mas-1999 form-1.pdf

0742-mas-1999 form-19.pdf

0742-mas-1999 form-26.pdf

0742-mas-1999 form-3.pdf

0742-mas-1999 form-8.pdf


Patent Number 213968
Indian Patent Application Number 742/MAS/1999
PG Journal Number 13/2008
Publication Date 31-Mar-2008
Grant Date 23-Jan-2008
Date of Filing 14-Jul-1999
Name of Patentee INDIAN SPACE RESEARCH ORGANISATION
Applicant Address ISRO HEADQUARTERS, DEPARTMENT OF SPACE, ANTHARIKSH BHAVAN, NEW BEL ROAD, BANGALORE 560 094,
Inventors:
# Inventor's Name Inventor's Address
1 DR. M. MANJUNATHA NAYAK C/O ADVANCED TRANSDUCERS DIVISION, TLF-LPSC-ISRO, DEPTSPACE, GOVT. OF INDIA, 80 FEET ROAD, HAL 2ND STAGE, H.P.O. BANGALORE-560 008,
2 K. SANKARAN C/O ADVANCED TRANSDUCERS DIVISION, TLF-LPSC-ISRO, DEPTSPACE, GOVT. OF INDIA, 80 FEET ROAD, HAL 2ND STAGE, H.P.O. BANGALORE-560 008,
PCT International Classification Number G01 F 01/66
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA