Measuring and testing – Liquid level or depth gauge – Float
Reexamination Certificate
2001-01-02
2001-08-07
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Float
C073S322500, C073S30400R, C702S055000
Reexamination Certificate
active
06269694
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a level sensor for detecting the level of a liquid or a powder or particulate accumulation (hereinafter referred to as a powder or particulate level).
One example of this type of level sensor is shown in FIG.
35
. This sensor includes a pipe member
90
having a plurality of vertically disposed proximity switches
90
a
, and a float
91
surrounding pipe member
90
and having a magnet
91
a
on its inner peripheral side.
The magnet
91
a
moves up and down with the float in response to the rise and fall of the liquid surface. In this level sensor, the level of liquid can be determined by sensing which proximity switch
90
a
the magnet
91
a
is next to.
The following problems exist in this known level sensor:
(1) Since sensing is possible only when the float
91
comes to a certain position where one of the proximity switches
90
a
is present, the liquid level can be determined only up to certain discrete values.
(2) Since the float
91
moves up and down with respect to the pipe member
90
, dust and the like can become clogged between the float
91
and the pipe member
90
, thereby inhibiting the smooth response of the float
91
, and resulting in failure to detect the level of the liquid. In other words, many mechanical elements end up with poor reliability.
(3) This sensor cannot detect the level of the interface between an upper liquid layer and a lower liquid layer.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a liquid level sensor which overcomes the limitations of the prior art.
It is another object of the present invention to provide a level sensor with which a liquid level or a powder or particulate level can be determined continuously with high reliability.
It is a further object of the present invention to provide a level sensor in which a level of the interface between two fluid layers can be detected.
Briefly stated, the present invention provides a sensor for detecting levels of fluids and particulate matter based on differences in dielectric constants of the various materials. The difference is reflected in different capacitance across electrodes immersed to different depths in such materials. A square-wave clock pulse is input into circuit composed of the capacitance and a resister in series. The output voltage is fed into a logic unit (such as exclusive-OR), which converts the exponential decay of the voltage into a pulse of uniform height with duration proportional to the time constant (proportional to the capacitance) of the exponential decay. The pulse is optionally fed through a low-pass filter to give a signal proportional to the duration.
According to an embodiment of the invention, there is provided a level sensor for detecting a level of one of liquid, and a particulate material comprising: a capacitance type variable capacitor having an electrode having a capacitance responsive to surrounding stray capacitance, a resistor connected with the variable capacitor to form an integration circuit, the integration circuit having a time constant responsive to the capacitance and a value of the resistor, a logic device, the integration circuit receiving a clock having a constant frequency and duty ratio, an output from the integration circuit is input to the logic device, and the integration circuit producing an output from the logic device which varies according to change in capacitance of a capacitance plus a stray capacitance of the variable capacitor in response to change in length of a portion of the electrode immersed in the material.
According to a feature of the invention, there is provided a level sensor for detecting a level of one of a liquid object and a particulate object comprising: an electrode susceptible to surrounding stray capacitance, a resistor connected with the electrode to form an integration circuit, a logic device, the integration circuit receiving clock of a constant frequency and duty ratio, an output from the integration circuit is input to the logic device, and an output from the logic device varies depending on a change in the stray capacitance produced in surroundings of the electrode in response to a change in length of a portion of the electrode immersed in the object.
According to a further feature of the invention, there is provided a level sensor for detecting a level of one of a liquid and a particulate material comprising: an electrode susceptible to surrounding stray capacitance, a capacitor, a fixed resistor, a logic device, the resistor and a combined element made up of the electrode and the capacitor constituting an integration circuit, the integration circuit receiving a clock having a constant frequency and duty ratio, an output from the integration circuit is input to the logic device, and an output from the logic device varies according to change in a capacitance of a capacitance of the fixed capacitor plus a stray capacitance of the electrode in response to a change in length of a portion of the electrode immersed in the object.
According to a still further feature of the invention, there is provided a level sensor for detecting a level of one of a liquid and a particulate material comprising: at least three electrodes mutually arranged in parallel to form at least two variable capacitors, associated fixed resistors respectively connected to the capacitors to form at least first and second integration circuits which have time constants different from each other, a logic device, the first and second integration circuits receiving a clock having a constant frequency and duty ratio, an output from the integration circuits is input to the logic device, and an output from the logic device varies depending on change in capacitance of a capacitance plus a stray capacitance of the variable capacitors in response to change in length of a portion of the variable capacitors immersed in the object.
According to another feature of the invention, there is provided a level sensor for detecting a level of an interface between an upper layer and a lower layer, the upper and lower layers having different dielectric constants comprising: a float, a capacitance type variable capacitor having two electrodes arranged mutually in parallel, the variable capacitor being supported by the float, a resistor connected to the variable capacitor to form an integration circuit, a logic device receiving an output of the integration circuit, the variable capacitor extending downward into the upper and lower layers when the float is floated on a surface of the upper layer, whereby a capacitance of the variable capacitance is varied by an amount related to a thickness of the upper layer, the integration circuit receiving a clock having a constant frequency and duty ratio, an output from the integration circuit is input to the logic device, and a duty ratio of an output of the logic device varies according to change in capacitance of a capacitance plus a stray capacitance of the variable capacitor in response to change in length of a portion of the capacitor immersed in the upper liquid layer.
According to another feature of the invention, there is provided a level sensor for detecting a level of an interface between an upper liquid layer and a lower liquid layer comprising: a float, a plurality of variable capacitors having electrodes arranged mutually in parallel at equal intervals supported on the float, resistors connected to respective variable capacitors to form integration circuits having different time constants, and a logic device, the float being floated on a liquid surface with the plurality of variable capacitors extending downward immersing the electrodes in the two liquid layers, the integration circuits receiving a clock having a constant frequency and duty ratio, an output from the integration circuit is input to the logic device and a duty ratio of an output of the logic device varies depending on capacitances of a capacitance plus a stray capacitance of the variable capacitors in response to change in length of a
Cygan Michael
Morrison Law Firm
Nitta Corporation
Williams Hezron
LandOfFree
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