Title of Invention

A SELF-CALIBRATING RESISTIVE GAUGE FOR THE MEASUREMENT OF LIQUID LEVELS

Abstract A self—cal ibrating resistive guage for the measurement of liquid levels comprising a measurement probe for being dipped in the said liquid, said probe being connected to means for determining the resistance Rm of the said probe which is equal to Xy where X is the level of the said liquid and Y is the resistivity/unit length of the said probe for a given liquid characterised by a reference probe for being fully immersed in the said liquid, said reference probe being connected to second means for determining the resistance Rr of the said reference probe which is equal to Ly where L is the length of the said reference probe and a divider for dividing the said
Full Text This invention relates to a self-calibrating resistive gauge for the measurement of liquid levels.
Levels of a liquid, e'specially of a liquid with good electrical conductivity, are conventionally measured by measuring the resistance between a pair of electrodes (a probe) dipped in the liquid. The probe is connected to means for determining the resistance such as a signal conditioning circuit.
However, this type of level measurement has one draw back, namely, the probe has to be calibrated time and again for liquids of different conductivities for obtaining any meamingful result- In spite of this shortcoming, such gauges ars popular in view of their simplicity and low cost.
This invention, accordingly, proposes a gauge which provides an output proportional to the liquid level, without the need for calibration. Any change in the quality
electrical conductivities.
The self-calibrating resistive gauge for the measurement of liquid levels, according to this invention!, comprises a measurement probe for being dipped in the said liquid, said probe being connected to means for determining the resistance Rm of the said probe which is equal to Xy where X is the level of the said liquid and y is the resistivity/unit length of the said probe for a given liquid characterised by a reference probe for being fully immersed in the said liquid, said reference probe being connected to second means for determining the resistance Rr of the said reference probe which is equal to Ly where L is the length of the said reference probe; and a divider for dividing the said two resistances to obtain X = L Rm. Rr This invention will now be described with reference to the accompanying drawings which illustrate, by way of example, one of the various possible embodiments of the gauge proposed herein,

Fig. 1 illustrating the measurement and reference probes
and
Fig.2 illustrating the signal conditioning circuits with divider
The measurement probe M (with the elements^ is intended for being dipped in the liquid whose level is to be measured. The depth of immersion of this probe is proportional to the level of the liquid to be measured.
The said probe is connected to means for determining the resistance Rm thereof.
On the other hand the reference probe R is intended for being fully immersed in the liquid. This probe is also connected to means for determining the resistance Rr thereof.
The Yeisi^^mt-^f^ is equal to Xy where X is the level of the said liquid and y is the resistivity/unit length of
4

the probe M for a given liquid.
The resistance Rr of the reierence probe is equal to Ly where L is the length of the said probe.
A dividerjl> is provided for dividing the said two
resistances to obtain X = L Rm
Rr The right hand side of the above equation can be seen
to be independent of the liquid characteristics y.
To realise the above equation, the aforementioned means, exemplified by the signal conditioning circuits illustrated in Fig.2 are employed.
The oscillator 01 of frequency fl is connected to the measurement probe M, the output current Al being fed to a converter CI the output of which is an a,c, voltage VI proportional to the resistance Rm. This voltage is applied at the input of PSD-l (phase sensitive detector). The oscillator output voltage is also sensed by PSD-l. The output of PSD-l is a d.c voltage proportional to Xy.

The oscillator 02 of -frequency +2 is connected to the reference probe R, the output current A2 being fed to a converter C2 the output of which is an a.c. voltage V2 proportional to the resistance Rr. This voltage is applied at the input of PSD-2 (phase sensitive detector). The oscillator output voltage is also sensed by PSD~2. The output of PSD-2 is a d.c voltage proportional to Ly,
The outputs of PSD~1 and PSD-2 are fed to a divider D
to obtain the ratic from which the above equation is
derived (X = L Rm) thus furnishing the level X
Rr regardless of the resistivity factor y.
The terms and expressions in this specification are of description and not of limitation, there being no intention in the use of such terms and expressions of excluding any equivalents of the features illustrated and described, but it is understood that various other embodiments of the gauge proposed herein are possible without departing from the scope and ambit of this invention.


We Claims
1. A self-calibrating resistive gauge for the
measurement of liquid levels comprising a measurement
probe for being dipped in the said liquid, said probe
being connected to means for determining the resistance
Rm of the said probe which is equal to Xy where X is
the level of the said liquid and y is the
resistivity/unit length of the said probe for a given
liquid characterised by a reference probe for being
fully iaimersed in the said liquid, said reference probe
being connected to second means for deterssining the
resistance Rr of the said reference probe ishich is
equal to Ly where L is the length of the said reference
probes and a divider for dividing the said two
resistances to obtain X = LRm.
2. A self-calibrating resistive gauge as claimed in
Claim 1 wherein the said first and second means each
comprise a signal conditioning circuit.
3. A self-calibrating resistive gauge for the

measurement of liquid levels substantially as herein described, with reference to, and as illustrated in, the accompanying drawings.


Documents:

521-mas-1997 abstract-duplicate.pdf

521-mas-1997 abstract.pdf

521-mas-1997 claims-duplicate.pdf

521-mas-1997 claims.pdf

521-mas-1997 correspondence-others.pdf

521-mas-1997 correspondence-po.pdf

521-mas-1997 description (complete)-duplicate.pdf

521-mas-1997 description (complete).pdf

521-mas-1997 drawings-duplicate.pdf

521-mas-1997 drawings.pdf

521-mas-1997 form-1.pdf

521-mas-1997 form-26.pdf


Patent Number 196336
Indian Patent Application Number 521/MAS/1997
PG Journal Number 30/2009
Publication Date 24-Jul-2009
Grant Date
Date of Filing 13-Mar-1997
Name of Patentee INDIAN INSTITUTE OF TECHNOLOGY
Applicant Address IIT P.O., CHENNAI - 600036
Inventors:
# Inventor's Name Inventor's Address
1 DR. VARADARAJAN JAGADEESH KUMAR INDIAN INSTITUTE OF TECHNOLOGY, IIT P.O., CHENNAI - 600036
2 DR. PAUL MARIO KOOLA INDIAN INSTITUTE OF TECHNOLOGY, IIT P.O., CHENNAI - 600036
PCT International Classification Number G01F19/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA