# US 10,308,035 B2 · Fluid level sensor and related methods > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,308,035 B2 - Document ID: US10308035B2 - Status: Granted - Kind: B2 - Application number: 15/891,565 - Filed: 2018-02-08 - Published: 2018-06-14 - Granted: 2019-06-04 - Earliest claimed: 2016-08-05 - Assignees: Hewlett-Packard Development Company, L.P. - Applicants: Hewlett-Packard Development Company, L.P. - Inventors: Andrew L. Van Brocklin; Paul A. Liebert; Adam L. Ghozeil; Scott A. Linn - Web page: https://patentgrep.com/patent/US10308035B2 ## CPC - B41J 2/17566: {Ink level or ink residue control} - B41J 2/0451: {for detecting failure, e.g. clogging, malfunctioning actuator} - B41J 2/04555: {detecting current} - B41J 2/0458: {controlling heads based on heating elements forming bubbles} - B41J 2/125: Sensors, e.g. deflection sensors {(nozzle clogging detection for cleaning reasons B41J2/16579; detection for compensation for failed nozzles B41J2/2139)} - B41J 2/14153: {Structures including a sensor} - B41J 2002/17579: {Measuring electrical impedance for ink level indication} - B41J: TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS ## Abstract In an embodiment, a fluid level sensor includes a sensor plate and a current source. The fluid level sensor also includes an algorithm to bias the current source such that current applied to the sensor plate induces a maximum difference in response voltage between a dry sensor plate condition and a wet sensor plate condition. ## Claims ### Claim 1 A fluid cartridge comprising: a nozzle; a fluid channel; a sensor plate on a floor of the channel; a current source coupled to the sensor plate to induce a voltage response across the sensor plate; a sensor circuit to determine the voltage response of the sensor plate to the current source, the voltage response indicating to what extent the sensor plate is in contact with fluid and with air; and an electronic controller to determine a bias for the current source such that the induced voltage response across the sensor plate has a maximum variation between wet and dry sensor plate conditions; wherein the electronic controller is to output a signal indicative of a fluid level based on the voltage response of the sensor plate. ### Claim 2 (depends on 1) The fluid cartridge of claim 1, the electronic controller to adjust the bias for the current source over time such that the induced voltage response across the sensor plate continues to have a maximum variation between wet and dry sensor plate conditions. ### Claim 3 (depends on 2) The fluid cartridge of claim 2, the electronic controller to: input a minimum stimulus to the current source; sample an induced voltage response at the minimum stimulus; input a maximum stimulus to the current source; sample an induced voltage response at the maximum stimulus; and determine a peak response stimulus from the induced voltage responses at the minimum and maximum stimuli. ### Claim 4 (depends on 1) The fluid cartridge of claim 1, the sensor circuit further comprising a switch to short out the sensor plate in a closed position during biasing of the current source, and to apply current from the current source to the sensor plate in an open position. ### Claim 5 (depends on 1) The fluid cartridge of claim 1, wherein the sensor plate comprises a sensor plate surface, a length of the sensor plate surface extending along the fluid channel toward and perpendicular to a firing axis of the nozzle. ### Claim 6 (depends on 5) The fluid cartridge of claim 5, wherein the sensor plate is located in the fluid channel upstream from the nozzle where an increase in backpressure associated with a depleted ink supply will pull an ink meniscus far enough back into the fluid channel that the sensor plate is exposed to air drawn through the nozzle. ### Claim 7 (depends on 1) The fluid cartridge of claim 1, the sensor circuit to determine the voltage response of the sensor plate to the current source to determine whether the sensor plate is in a wet or dry condition. ### Claim 8 A fluid cartridge comprising: a nozzle; a fluid channel; a sensor plate on a floor of the channel; a current source coupled to the sensor plate to induce a voltage response across the sensor plate; a sensor circuit to determine the voltage response of the sensor plate to the current source, the voltage response indicating to what extent the sensor plate is in contact with fluid and with air; and an electronic controller to determine a bias for the current source such that the induced voltage response across the sensor plate has a maximum variation between wet and dry sensor plate conditions; wherein the electronic controller is to output a signal indicative of a fluid level based on the voltage response of the sensor plate; and further comprising a register operated by the electronic controller, the register to provide input to a Digital-to-Analog Converter (DAC) and Sample & Hold Circuit to provide a bias to the current source. ### Claim 9 (depends on 8) The fluid cartridge of claim 8, further comprising a measurement module of the electronic controller to initiate a fluid measurement cycle during which the measurement module controls the sensor circuit through a state machine. ### Claim 10 (depends on 9) The fluid cartridge of claim 9, the state machine to initiate a priming event, provide a delay period, and, after the delay period, operate a switch to apply current from the current source to the sensor plate to induce the voltage response across the sensor plate. ### Claim 11 (depends on 10) The fluid cartridge of claim 10, the state machine further to provide a second delay period, after which, the state machine is to control a second Sample & Hold Circuit to sample and hold an analog response voltage at the sensor plate, operate an Analog-to-Digital Converter (ADC) on the sampled analog response voltage to produce a digitized response voltage that is stored in a register. ### Claim 12 (depends on 11) The fluid cartridge of claim 11, the measurement module to compare the digitized response voltage to a threshold to determine if the sensor plate is in a wet or dry condition. ### Claim 13 (depends on 8) The fluid cartridge of claim 8, wherein the current source comprises three current producing transistors to produce current in three different current ranges. ### Claim 14 (depends on 13) The fluid cartridge of claim 13, wherein the current source further comprises a range select circuit to apply voltage from the DAC to one of the three current producing transistors. ### Claim 15 A fluid cartridge comprising: a nozzle; a fluid channel; a sensor plate on a floor of the channel; a current source coupled to the sensor plate to induce a voltage response across the sensor plate; a sensor circuit to determine the voltage response of the sensor plate to the current source, the voltage response indicating to what extent the sensor plate is in contact with fluid and with air; and an electronic controller to determine a bias for the current source such that the induced voltage response across the sensor plate has a maximum variation between wet and dry sensor plate conditions; wherein the electronic controller is to output a signal indicative of a fluid level based on the voltage response of the sensor plate; and wherein the sensor plate is located in the fluid channel where an increase in backpressure associated with a depleted ink supply will pull an ink meniscus far enough back into the fluid channel that the sensor plate is exposed to air drawn through the nozzle. ### Claim 16 (depends on 15) The fluid cartridge of claim 15, the electronic controller to adjust the bias for the current source over time such that the induced voltage response across the sensor plate continues to have a maximum variation between wet and dry sensor plate conditions. ### Claim 17 (depends on 15) The fluid cartridge of claim 15, the sensor circuit further comprising a switch to short out the sensor plate in a closed position during biasing of the current source, and to apply current from the current source to the sensor plate in an open position. ### Claim 18 (depends on 15) The fluid cartridge of claim 15, wherein the current source comprises three current producing transistors to produce current in three different current ranges. ### Claim 19 (depends on 18) The fluid cartridge of claim 18, wherein the current source further comprises a range select circuit to apply a bias input to one of the three current producing transistors. ### Claim 20 (depends on 15) The fluid cartridge of claim 15, further comprising: a register operated by the electronic controller, the register to provide input to a Digital-to-Analog Converter (DAC) and Sample & Hold Circuit to provide a bias to the current source; and a measurement module of the electronic controller to initiate a fluid measurement cycle during which the measurement module controls the sensor circuit through a state machine.