Fluid level meter

Claim 2

A fluid level meter having enhanced resolution over portions of a fluid level range over which the meter is to operate, said meter comprising: A. first, second and third fluid level sensors for immersion in the fluid whose level is to be measured and providing, in response to a driving signal, outputs indicative of the extent to which they are immersed 1. said first sensor providing an output corresponding to a first portion of said fluid level range, 2. said third sensor providing an output corresponding to a third portion of said fluid level range, 3. said second sensor providing an output corresponding to a second portion of said fluid level range intermediate said first and third portions, 4. said first, second and third portions collectively defining said fluid level range, 5. said second sensor being characterized by a resolution less than that of said first and third sensors, B. means for electrically driving said sensors, C. an indicator, and D. switching means responsive to the fluid level 1. for connecting only the first sensor to the indicator when the fluid level is in said first portion and 2. for connecting to the indicator only the third sensor and a signal corresponding to the height of both said first and second sensors when the fluid level lies in said third portion.

Claim 3

for connecting to the indicator only the third sensor and a signal corresponding to the height of both said first and second sensors when the fluid level lies in said third portion.

Claim 4

for connecting to the indicator only the third sensor and a signal corresponding to the height of both said first and second sensors when the fluid level lies in said third portion.

Claim 5

said third sensor providing an output corresponding to a third portion of said fluid level range,

Claim 6

said third sensor providing an output corresponding to a third portion of said fluid level range,

Claim 7

providing, in response to a driving signal, outputs indicative of the extent to which they are immersed,

Claim 8

providing, in response to a driving signal, outputs indicative of the extent to which they are immersed,

Claim 9

providing an output indicative of the extent to which it is immersed in response to a driving signal,

Claim 10

providing an output indicative of the extent to which it is immersed in response to a driving signal,

Claim 11

providing, in response to a driving signal, an output indicative of the extent to which it is immersed,

Claim 12

providing, in response to a driving signal, an output indicative of the extent to which it is immersed,

Claim 13

first and second separate inner electrodes spaced from said outer electrode and forming first and second capacitive sensors respectively therewith, and B. which includes means for each sensor for compensating for the empty value of each said sensor, said compensating means comprising:

Claim 14

first and second separate inner electrodes spaced from said outer electrode and forming first and second capacitive sensors respectively therewith, and B. which includes means for each sensor for compensating for the empty value of each said sensor, said compensating means comprising:

Claim 15

a trimmer capacitor,

Claim 16

a trimmer capacitor,

Claim 17

connecting the reference level generator output as a reference input to the signal generator when the fluid level is below the second minimum level.

Claim 18

connecting the reference level generator output as a reference input to the signal generator when the fluid level is below the second minimum level.

Claim 19

A fluid level meter according to claim 1 in which said switching means is actuated by the first and third sensor outputs respectively.

Claim 20

said second sensor providing an output corresponding to a second portion of said fluid level range intermediate said first and third portions,

Claim 21

said second sensor providing an output corresponding to a second portion of said fluid level range intermediate said first and third portions,

Claim 22

formed from first, second and third distinct inner electrodes and a common outer electrode spaced from said inner electrodes,

Claim 23

formed from first, second and third distinct inner electrodes and a common outer electrode spaced from said inner electrodes,

Claim 24

a transformer having a primary winding connected in parallel with the outer electrode driving signal and a secondary winding having an intermediate portion thereof connected to a common reference potential, opposite ends of the secondary winding providing opposite voltages with respect to said common potential,

Claim 25

a transformer having a primary winding connected in parallel with the outer electrode driving signal and a secondary winding having an intermediate portion thereof connected to a common reference potential, opposite ends of the secondary winding providing opposite voltages with respect to said common potential,

Claim 26

having a resolution of a first magnitude, and

Claim 27

having a resolution of a first magnitude, and

Claim 28

having a resolution less than that of said first sensor, and

Claim 29

having a resolution less than that of said first sensor, and

Claim 30

A fluid level meter according to claim 2 which includes first and second comparators for comparing the outputs of said first and third sensors with first and second predetermined reference signals corresponding to first and second fluid reference levels, respectively, the first comparator enabling the switching means to connect only the first sensor to the indicator when the fluid level is below said first reference level and enabling the switching means to connect only the third sensor to the indicator when the fluid level is above said second reference level.

Claim 31

A fluid lEvel meter according to claim 1 which includes: A. a reference sensor positioned to provide a reference output whenever the fluid level is above a first minimum level, B. a reference level generator providing an output corresponding to the output provided by the reference sensor when the fluid level is above a second minimum level, C. a driving generator providing an output controlled by a reference input applied thereto, and D. a switch

Claim 32

operating over a second fluid level range greater than the first fluid level range and forming the remaining portion of the total range level to be measured, and C. indicator means selectively responsive to said sensor outputs to provide an indication of the fluid level within said total level range; and D. switching means responsive to the level of fluid within said first sensor for applying only the first sensor output to the indicator when the fluid is within a first subrange of said total range and applying both sensor outputs to the indicator when the fluid is outside said first subrange.

Claim 33

operating over a second fluid level range greater than the first fluid level range and forming the remaining portion of the total range level to be measured, and C. indicator means selectively responsive to said sensor outputs to provide an indication of the fluid level within said total level range; and D. switching means responsive to the level of fluid within said first sensor for applying only the first sensor output to the indicator when the fluid is within a first subrange of said total range and applying both sensor outputs to the indicator when the fluid is outside said first subrange.

Claim 34

operating over a first fluid level range forming a portion of the total range level to be measured, B. a second fluid level sensor:

Claim 35

operating over a first fluid level range forming a portion of the total range level to be measured, B. a second fluid level sensor:

Claim 36

a potentiometer connected across said secondary winding and having a movable wiper arm providing an output voltage whose magnitude and polarity are dependent on the position of said wiper arm,

Claim 37

a potentiometer connected across said secondary winding and having a movable wiper arm providing an output voltage whose magnitude and polarity are dependent on the position of said wiper arm,

Claim 38

said first, second and third portions collectively defining said fluid level range,

Claim 39

said first, second and third portions collectively defining said fluid level range,

Claim 40

the outputs being taken from the respective inner electrodes,

Claim 41

the outputs being taken from the respective inner electrodes,

Claim 42

the first and third sensors providing outputs corresponding to first and third fluid level ranges, respectively, including said portions,

Claim 43

the first and third sensors providing outputs corresponding to first and third fluid level ranges, respectively, including said portions,

Claim 44

said second sensor being characterized by a resolution less than that of said first and third sensors, B. means for electrically driving said sensors, C. an indicator, and D. switching means responsive to the fluid level

Claim 45

said second sensor being characterized by a resolution less than that of said first and third sensors, B. means for electrically driving said sensors, C. an indicator, and D. switching means responsive to the fluid level

Claim 46

A fluid level meter according to claim 4 in which said switch is actuated in response to the output of the first sensor.

Claim 47

means connecting the output of a selected sensor to a summing junction to apply a signal thereto proportional to the capacitance of said sensor,

Claim 48

means connecting the output of a selected sensor to a summing junction to apply a signal thereto proportional to the capacitance of said sensor,

Claim 49

means connecting said reference capacitor between said summing junction and one end of said secondary winding to provide a signal to said junction whose phase is of opposite polarity to that of said sensor output, and

Claim 50

means connecting said reference capacitor between said summing junction and one end of said secondary winding to provide a signal to said junction whose phase is of opposite polarity to that of said sensor output, and

Claim 51

the second sensor providing an output corresponding to a second fluid level range intermediate said first and third ranges and having a resolution less than the resolution of such first and third sensors, B. means for applying a driving signal to said outer electrode, C. an indicator for providing an indication of the fluid level within said fluid level range in response to inputs applied thereto from said sensors, D. switching means responsive to the sensor outputs to connect the outputs of selected ones of said sensors to said indicator dependent on the location of the fluid level E. a reference sensor providing, in response to said driving signal, an output indicative of the level of a fluid in which it is immersed, F. means for subtracting from each level sensor output and from the reference sensor output a signal corresponding to the output provided by each said sensor when the sensor is not immersed in fluid, to thereby establish the zero point of the level range, G. means for varying the driving signal in accordance with the reference sensor output to maintain the current through said sensor constant, H. means for summing the outputs of each of the sensor capacitors, I. means for disabling the level sensor subtracting signal means while the sensor capacitors and reference sensors are empty, and J. means for setting said indicator to read full-scale to thereby establish the full scale reading of said meter without immersion of said sensor.

Claim 52

the second sensor providing an output corresponding to a second fluid level range intermediate said first and third ranges and having a resolution less than the resolution of such first and third sensors, B. means for applying a driving signal to said outer electrode, C. an indicator for providing an indication of the fluid level within said fluid level range in response to inputs applied thereto from said sensors, D. switching means responsive to the sensor outputs to connect the outputs of selected ones of said sensors to said indicator dependent on the location of the fluid level E. a reference sensor providing, in response to said driving signal, an output indicative of the level of a fluid in which it is immersed, F. means for subtracting from each level sensor output and from the reference sensor output a signal corresponding to the output provided by each said sensor when the sensor is not immersed in fluid, to thereby establish the zero point of the level range, G. means for varying the driving signal in accordance with the reference sensor output to maintain the current through said sensor constant, H. means for summing the outputs of each of the sensor capacitors, I. means for disabling the level sensor subtracting signal means while the sensor capacitors and reference sensors are empty, and J. means for setting said indicator to read full-scale to thereby establish the full scale reading of said meter without immersion of said sensor.

Claim 53

A fluid level meter according to claim 5 which includes a comparator having the output of the first sensor applied as a first input thereto, and having a signal corresponding to the second minimum level applied as a second input thereto, and providing an output whenever the first input exceeds the second input.

Claim 54

A fluid level meter according to claim 1 which includes a comparator having the output of the third sensor applied as a first input thereto and a reference signal corresponding to the lower level of the second fluid level range applied as a second input thereto, said comparator providing an output causing said fixed magnitude to be set into said indicator when the first comparator input exceeds the second comparator input.

Claim 55

means connecting said trimmer capacitor between said summing junction and said wiper arm to thereby apply to said summing junction a signal whose magnitude and phase is selectable to add to, or subtract from, the reference capacitor output.

Claim 56

means connecting said trimmer capacitor between said summing junction and said wiper arm to thereby apply to said summing junction a signal whose magnitude and phase is selectable to add to, or subtract from, the reference capacitor output.

Claim 57

A fluid level meter having enhanced resolution over portions of a fluid level range over which the meter is to operate, said meter comprising: A. first, second and third capacitive sensors

Claim 58

A fluid level meter having enhanced resolution over portions of a fluid level range over which the meter is to operate, said meter comprising: A. first, second and third capacitive sensors

Claim 59

A fluid level meter according to claim 8 which includes a safety barrier for applying the driving signal tO the sensors, said barrier comprising: A. a transformer having a primary winding for connection to the driving signal and a second winding for connection to the outer electrode, B. a current limiting resistor in series with the primary winding, C. a current limiting resistor in series with the secondary winding, and D. overload voltage protection means connected across said primary and forming a shunt path for current when a voltage in excess of a predetermined amount is applied to said primary.

Claim 60

A fluid level meter according to claim 9 in which the overload voltage protection means comprises first and second pairs of zener diodes, each pair being connected back-to-back across said primary and being separated from the other by said current limiting resistor.

Claim 61

A fluid level meter according to claim 8 which includes a safety barrier for receiving the driving voltage from each said sensor, each said barrier comprising: A. a transformer having a primary winding for receiving the sensor output and a secondary winding for connection to said indicator, B. a current limiting resistor in series with the one of said windings, C. a current limiting resistor in series with the other of said windings, D. overload voltage protection means connected across one of said windings forming a shunt path for current when a voltage in excess of a predetermined amount is applied to the other of said windings.

Claim 62

A fluid level meter according to claim 11 in which the overload voltage protection means comprises first and second pairs of zener diodes, each pair being connected back-to-back across said one winding and being separated from the other pair by the current limiting resistor in said winding.

Claim 63

A fluid level meter according to claim 8 in which the means for subtracting from each leve sensor output a signal corresponding to the otuput provided by each respective sensor when the sensor is not immersed in fluid comprises a reference capacitor having a nominal value approximately that of the sensor capacitor to be compensated, and which includes means for compensating each sensor capacitor for the empty value thereof, said means comprising: A. at least one trimming capacitor for use in connection with the reference capacitor, B. a summing junction, C. means connecting tthe sensor capacitor output to said junction, D. means connecting one end of the reference capacitor to the summing junction, E. means connecting the other end of the reference capacitor to a source of potential of such polarity as to apply a signal to the summing junction through the capacitor of a polarity opposite that of the sensor capacitor output, F. means connecting one end of the trimming capacitor to the summing junction, G. means connecting the other end thereof to a source of potential of selectable polarity so as to apply a signal of selectable polarity to the junction through the trimming capacitor, the sum of the signals applied through the reference and trimming capacitors being equal in magnitude and opposite in polarity to that applied to said junction by the sensor capacitor.

Claim 64

A fluid level meter according to claim 13 which includes means for compensating for stay pick-up at said summing junction, said means comprising: A. a source of alternating voltage in phase with the voltage applied to the reference and trimming capacitors and providing voltages of opposite polarity with respect to a common reference, B. first and second potentiometers, each having a movable wiper arm and having opposite ends connected across said source to terminals of opposite polarity, C. a capacitor connected between a first wiper arm and said summing junction, and D. means connecting a second wiper arm to said summing junction, E. whereby in-phase and quadrature signal components may be applied to said summing junction.

Claim 65

A fluid level meter according to claim 13 in wHich a portion of the driving signal applied to the sensor capacitor is also applied to the reference and trimming capacitors.

Claim 66

A fluid level meter according to claim 8 including a synchronous detector connected in electrical circuit between each said sensor and said indicator for detecting the sensor outputs prior to application to said indicator.

Claim 67

A fluid level meter having greater resolution over a first fluid level range than over a second fluid level range, comprising: A. a first fluid level sensor;

Claim 68

A fluid level meter having greater resolution over a first fluid level range than over a second fluid level range, comprising: A. a first fluid level sensor;

Claim 69

A fluid level meter according to claim 17 in which said switching means comprises: A. a comparator for comparing the first sensor output to a predetermined reference level signal and supplying a selected output when said sensor output exceeds said reference level, and B. a gate responsive to said first comparator output for connecting said first sensor output to said indicator means.

Claim 70

A fluid level meter according to claim 18 which includes: A. means for summing the outputs of said first and second sensors prior to application to said indicator means, B. a second comparator for comparing the first sensor output to a second reference level and providing a selected output when said second sensor output exceeds said second reference level, and C. a second gate responsive to the second comparator output to connecting the summed sensor outputs to said indicator.

Claim 71

A fluid level meter according to claim 17 in which said first and second fluid level sensors are formed from inner and outer coaxial electrodes, the outer electrode being electrically continuous, the inner electrode being electrically discontinuous to form first and second electrode segments corresponding to said first and second sensors.

Claim 72

A fluid level meter according to claim 20 which includes compensating means for each sensor capacitor for compensating for the empty value of each said capacitor, said means comprising: A. a reference capacitor having a nominal value approximately that of the sensing capacitor to be compensated, B. a trimming capacitor for modifying the effective value of said reference capacitor, C. means for driving said reference capacitor with a driving signal of opposite phase to the driving signal applied to the corresponding sensor capacitor whereby the reference capacitor provides an output of opposite polarity output to the sensor capacitor output, D. means for driving said trimmer capacitor with a driving signal of adjustable magnituded and whose phase is selectable to be the same as, or opposite to, the phase of said sensor capacitor driving signal, and E. means connecting the reference and trimmer capacitor outputs and the corresponding sensor capacitor ouTput to a common summing junction.

Claim 73

A fluid level meter according to claim 21 which includes means for compensating for quadrature effects in the sensor capacitor and which comprises applying to said summing junction a driving signal of selectable amplitude and polarity and in phase with the driving signal applied to the sensor capacitor.

Claim 74

A fluid level meter according to claim 17: A. in which said first and second sensors are formed from:

Claim 75

A fluid level meter according to claim 23 which includes: A. a second potentiometer connected across said secondary winding and having a movable wiper arm providing an output voltage whose magnitude and polarity are dependent on the position of said arm, and B. means connecting said wiper arm to said summing junction to add or subtract a signal therefrom in quadrature relation with signal supplied by the reference and trimmer capacitors.

Claim 76

A fluid level meter according to claim 24 which includes means for compensating for stray signal pick-up at said summing junction, said means comprising: A. a potentiometer having a movable wiper arm and bridged across at least a portion of said transformer secondary at points which are of opposite polarity, B. a capacitor connected between said wiper arm and said summing junction and providing a corrective signal of selectable magnitude and a first phase to said junction, C. a second potentiometer having a movable wiper arm and bridged across said first potentiometer, and D. means connecting the wiper arm of said second potentiometer to said summing junction to thereby provide thereto a corrective signal of selectable magnitude and a second phase in quadrature with said first phase.

Claim 77

A fluid level meter according to claim 17 including means to preset said indicator with a reference number corresponding to the height of a reference level of one of said sensors above a selected reference datum, said indicator being adapted to total said number and a number corresponding to the output of the other of said sensors when the fluid is sensed by said other sensor to thereby provide an indication of fluid height above said reference datum.

Claim 78

A fluid level meter according to claim 26 in which the indicator includes: A. a counter, B. means converting a voltage from said other Sensor to a pulse train containing a number of pulses proportional to the magnitude of said voltage for driving said counter, C. a storage register containing said reference number, and D. a gate interposed between said counter and said register and energizable to preset said counter with the number in said register.

Claim 79

A fluid level meter according to claim 27 in which said register is manually settable to any of a plurality of numbers.

Claim 80

A fluid level meter according to claim 17 which includes means for supporting said sensors in said tank, said means comprising: A. a sleeve of a low friction, electrically insulating material for circumferentially engaging said sensor, B. a clamp surrounding said sleeve and adapted for attachment to the tank, and C. said sensor axially moving in said sleeve in response to changes in sensor dimension caused by temperature changes.