CALIBRATION

BACKGROUND

[0001] Printing devices, such as standalone printers, are devices that output colorant onto print media like paper to form images on the print media. One type of printing device is an inkjet-printing device, which is more generally a fluid-ejection device. An inkjet-printing device can print ink different colors of corresponding to the colors of a color space to form full color images on print media. BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 is a diagram of a portion of an example fluid-ejection device including a reservoir, a fluid level gauge sensor, and a supply pump fluidically interconnecting the reservoir to a fluid supply.

[0003] FIG. 2 is a flowchart of an example method for cross-calibrating a supply pump of a fluid-ejection device and a fluid level gauge sensor for a reservoir of the device.

[0004] FIG. 3 is a flowchart of an example method for refilling a reservoir of a fluid-ejection device after a supply pump of the device and a fluid level gauge sensor for the reservoir have been cross-calibrated.

[0005] FIG. 4 is a block diagram of an example fluid-ejection device.

DETAILED DESCRIPTION

[0006] As noted in the background section, one type of printing device is an inkjet-printing device, which is more generally a fluid-ejection device. Inkjet-printing devices can include those used in smaller residential, office, and even enterprise environments, in which ink supplies may be integrated within printheads and self-contained within the devices themselves. In large- scale commercial and some enterprise environments, however, due to the continuous nature of the printing that occurs within these environments or for cost considerations, the ink supplies may be located external to the printing devices, permitting the usage of larger supplies of ink. In a sort of hybrid of these two types of printing devices, a printing device may include an internal reservoir that is periodically refilled from an external ink supply.

[0007] A user may thus periodically fluidically connect an ink supply to a printing device to refill the internal reservoir of the device. The user may have to manually determine that the reservoir has become empty or is running low on ink. The printing device may instead include a sensor to detect when the reservoir has become empty or is running low on ink, and alert the user that the reservoir should be refilled soon by fluidically connecting an ink supply to the printing device. Such a sensor can be particularly useful where the reservoir is disposed within the printing device in such a way that it is hidden from view, preventing the user from easily visually inspecting the reservoir without opening the device.

[0008] Such a sensor, however, is a single point of failure within the printing device. This means that if the sensor fails, the user will not be alerted to the reservoir becoming empty or running low on ink. Potentially more disastrous, the reservoir may be overfilled during refilling if the sensor has failed, or if the sensor is not properly calibrated, which can result in damage to the printing device. In this respect, the sensor within the reservoir may also be therefore used to detect when the reservoir has become full while being refilled from an external supply of ink. A pump fluidically interconnecting the ink supply to the reservoir may be employed to refill the reservoir in this respect.

[0009] Techniques described herein cross-calibrate a supply pump that fluidically interconnects an external fluid supply to a reservoir of a printing device and a fluid level gauge sensor within the reservoir. Both the supply pump and the fluid level gauge sensor can be used to measure the amount of fluid within the reservoir during refilling of the reservoir from the external fluid supply. The techniques described herein therefore provide redundancy, eliminating a single point of failure, and thus minimizing the potential for internal printing device damage from occurring due to overfilling. Cross- calibration of the supply pump and the fluid level gauge sensor can also be used to detect failure and degradation of both the pump and the sensor, as well as predict such failure and degradation, which can decrease printing device servicing costs and improve printing device reliability.

[0010] FIG. 1 shows a portion of an example fluid-ejection device 100. The fluid-ejection device 100 can be an inkjet-printing device, in which case the fluid that the device 100 ejects can include ink. The fluid-ejection device 100 includes a reservoir 102, a fluid level gauge sensor 104 for the reservoir 102, and a supply pump 106. The reservoir 102 and the supply pump 106 are fluidically interconnected via a fluid channel 108, which can include tubing, and by which the supply pump 106 inlets the fluid 116 into the reservoir 102.

[0011] Another fluid channel 114 is fluidically connected to the reservoir 102, from which the fluid 116 is outlet towards a fluid-ejection engine 118 of the device 100. The fluid channel 114 can also include tubing. The fluid- ejection engine 118 is or includes the components of the fluid-ejection device 100 that actually eject fluid from the device 100. For instance, in the case of an inkjet-printing device, the fluid-ejection engine 118 can be or include an inkjet printhead, or multiple printheads, which can output the fluid onto a print medium like paper to form an image on the medium. Such printheads can be considered a print mechanism by which images are printed on print media.

[0012] A fluid supply 110 can be external and removably connectable to the fluid-ejection device 100. The fluid supply 110 can be a starter fluid supply that is provided with the fluid-ejection device 100, and which can be of a known volume to permit cross-calibration of the supply pump 106 and the fluid level gauge sensor 104. The fluid supply 110 can be a non-starter fluid supply, which may not be of known volume in a sufficiently precise manner to permit cross-calibration, and/or which may be of greater volume than a starter fluid supply. A starter fluid supply may also be referred to as a calibration fluid supply.

[0013] The supply pump 106 is fluidically interconnected with the fluid supply 110 via a fluid channel 112. The fluid channel 112 can, like fluid channels 108 and 114, include tubing. The supply pump 106 thus fluidically interconnects the reservoir 102 and the external fluid supply 110, via the fluid channels 108 and 112. It is noted that there can be a supply pump 106 and a reservoir 102, with associated fluid channels 108,112, and 114 and an associated fluid supply 110, for each different type of fluid that the fluid- ejection device 100 uses. For instance, if the fluid-ejection device 100 is an inkjet-printing device, then there may be a supply pump 106, a reservoir 102, and so on, for each different color of ink that the device 100 can output.

[0014] In operation, when the fluid-ejection device 100 is first deployed, the reservoir 102 is empty, and may be in a dry or near dry state. A starter external fluid supply 110 of known volume that may ship with the fluid-ejection device 100 is connected to the channel 112. The supply pump 106 pumps the fluid 116 into the reservoir 102 from the external fluid supply 110, until the starter fluid supply 110 is empty. During this filling of the reservoir 102, the supply pump 106 and the fluid level gauge sensor 104 are cross-calibrated against one another, so that both the pump 106 and the sensor 104 can subsequently monitor refilling of the reservoir 102 from a non-starter external fluid supply 110 in an accurate manner. However, a calibration external fluid supply 110 may be subsequently connected to recalibrate the supply pump 106 and the fluid level gauge sensor 104 as appropriate.

[0015] When the pump 106 has transferred the fluid 116 into the reservoir 102 from the starter external fluid supply 110, therefore, this fluid supply 110 can be disconnected from the fluid channel 112. In one

implementation, no additional fluid supply 110 may be connected to the fluid channel 112 until the reservoir 102 has to be refilled due to the fluid-ejection engine 118 depleting the fluid 116 from the reservoir 102. In another implementation, however, a non-starter fluid supply 110 may be connected to the fluid channel 112 after cross-calibration of the supply pump 106 and the fluid level gauge sensor 104, so that refilling can subsequently occur without user involvement. As noted above, a non-starter or other non-calibration fluid supply may differ from a starter or other calibration fluid supply in that the former may not be of as precisely known volume as the latter, and/or the former may be of greater volume than the latter.

[0016] During operation of the fluid-ejection device 100, the fluid- ejection engine 118 ejects the fluid 116 from the reservoir 102 as provided via the fluid channel 114. The supply pump 106 does not transfer further fluid 116 into the reservoir 102 while the fluid-ejection engine 118 is ejecting the fluid 116, even if an external fluid supply 110 is connected to the fluid channel 112. When the fluid-ejection engine 118 has depleted the fluid 116 from the reservoir 102, the fluid level gauge sensor 104 can detect that the reservoir 102 is empty, or that the level of the fluid 116 within the reservoir 102 is below a threshold. At that time, fluid ejection by the fluid-ejection engine 118 pauses.

[0017] A user may be notified that the reservoir 102 has to be refilled with additional fluid 116. Such user notification occurs in an implementation in which a fluid supply 110 is connected just when the reservoir 102 has to be filled. More generally, user notification occurs if there is no fluid supply 110 is connected to the fluid channel 112. In an implementation in which a fluid supply 110 can remain connected to the fluid channel 112 after the reservoir 102 has been filled with the fluid 116, the user may thus not be notified that the reservoir 102 as to be refilled, and refilling may automatically occur, if there is a fluid supply 110 currently connected to the fluid channel 112.

[0018] If an external fluid supply 110 is currently connected to the fluid channel 112, or if not, once the user has connected an external fluid supply 110 to the fluid channel 112, the supply pump 106 can then refill the fluid 116 into the reservoir 102 from the fluid supply 110. During refilling, both the supply pump 106 and the fluid level gauge sensor 104, as have been cross- calibrated against one another, can monitor the refilling process. Monitoring the refilling process can ensure that the reservoir 102 is not overfilled

(or underfilled).

[0019] The fluid-ejection engine 118 may not eject fluid while refilling occurs. This permits the fluid level gauge sensor 104 to be used to monitor the refilling process. Otherwise, if refilling occurs while the fluid-ejection engine 118 is ejecting fluid, the engine 118 will deplete the fluid 116 from the reservoir 102 as the fluid 116 is pumped into the reservoir 102, and

monitoring by the sensor 104 may not be accurate. However, ejection of fluid can occur during refilling if just the supply pump 106 is used to monitor the refilling process.

[0020] During refilling, the supply pump 106 monitors the volume of fluid that it is pumping from the fluid channel 112 connected to the external fluid supply 110 to the fluid channel 108 connected to the reservoir 102. That is, the supply pump 106 monitors the volume of fluid that it is pumping from the fluid supply 110 to the reservoir 102. The fluid level gauge sensor 104 monitors the volume of the fluid 116 within the reservoir 102. The supply pump 106 can cease pumping fluid either when the pump 106 determines that it has pumped a sufficient volume of the fluid 116 into the reservoir 102 to fill the reservoir 102, when the fluid level gauge sensor 104 determines that the reservoir 102 has been filled with this sufficient volume of the fluid 116, or when both the pump 106 and the sensor 104 make their respective

determinations. Once refilling has been completed, the fluid-engine engine 118 can again start ejecting the fluid 116 if it has been suspended. [0021] FIG. 2 shows an example method 200 for cross-calibrating the supply pump 106 of the fluid-ejection device 100 and the fluid-level gauge sensor 104 of the reservoir 102 of the device 100. The method 200 can be implemented as instructions or other program code stored on a non-transitory computer-readable data storage medium and executed by the fluid-ejection device 100. For example, a processor or other hardware logic of the device 100 can perform the method 200.

[0022] The method 200 can begin when the reservoir 102 is an empty state and a starter fluid supply 110 has been fluidically connected to the fluid- ejection device 100 (202). The starter fluid supply 110, as has been noted, is synonymously referred to herein as a calibration fluid supply 110, which is a supply of fluid of known volume to a sufficient degree of precision to permit cross-calibration of the supply pump 106 and the fluid-level gauge sensor 104. That the reservoir 102 is an empty state means that the reservoir 102 is in a dry or a near-dry state. When the fluid-ejection device 100 is first deployed, for instance, the reservoir 102 may be in a dry state. If the fluid-ejection device 100 is subsequently recalibrated via re-performing the method 200, the reservoir 102 may be in a near-dry state, since there may be some fluid 116 remaining at the bottom of the reservoir 102 that cannot be pumped or drained from the reservoir 102.

[0023] Pumping of the fluid 116 into the reservoir 102 from the external fluid supply 110 via the pump 106 is then initiated (204). That is, the pump 106 starts pumping the fluid from the fluid channel 112 to the fluid channel 108. To move fluid from the reservoir 102 from the external fluid supply to the reservoir 102, a component of the pump 106, such as an electric motor, rotates. The pump 106 can thus be considered a rotary, or centrifugal, pump. Within the pump 106, there may be vanes or an impeller that rotates along an axis, as caused by the motor, or there can be a long screw, or auger, that rotates.

[0024] As the fluid 116 is pumped from the external fluid supply 110 into the reservoir 102 through the fluid channels 108 and 112, the number of pump revolutions is counted (206). The pump revolutions can be counted by using a pump revolution sensor, which may be integrated within the pump 106 itself. For example, the pump revolution sensor may be an optical or magnetic encoder.

[0025] In one implementation, there are what are referred to as specified numbers of revolution. For instance, the specified numbers of revolutions can be multiples of a base revolution count, such as 500 or 1 ,000 revolutions. In this respect, the specified number of revolutions can be based on time: if the pump 106 rotates at 1 ,000 rotations per minute (rpm), then the specified number of revolutions can be every thirty seconds or every minute, which corresponds to every 500 or 1 ,000 revolutions, respectively.

[0026] In such an implementation, each time a specified number of revolutions of the pump 106 has been reached (208), the fluid level gauge sensor 104 has its value sampled (210). If the specified number of

revolutions is 1 ,000, for example, then this means at 1 ,000 revolutions, at 2,000 revolutions, and so on, the fluid level gauge sensor 104 has its value sampled. The specified number of revolutions can further include zero; that is, the fluid level gauge sensor 104 can have its value sampled at the time of, or prior to, starting the pump 106. [0027] The value of the fluid level gauge sensor 104 can be a raw electrical value, such as voltage or current, that corresponds linearly or non- linearly with the level - and thus volume - of the fluid 116 within the reservoir 102. The fluid level gauge sensor 104 may be a float sensor, or a hydrostatic measurement device like a differential pressure level sensor. The fluid level gauge sensor 104 may be a load cell or strain gauge device. Other types of fluid level gauge sensors include magnetic level gauges, capacitance transmitters, and magnetorestrictive, ultrasonic, laser, and radar level transmitters.

[0028] The pump 106 continues until the fluid from the starter fluid supply 110 is empty (212) -e.g., the pump 106 is no longer pumping any fluid into the reservoir 102 while running. The starter fluid supply 110 at this time can therefore be in a near dry state. The starter fluid supply 110 can be detected as being empty at the external fluid supply 110 itself, at the channel 112 or 108, or at the pump 106. At the external fluid supply 110, a weight or other type of fluid sensor may be employed to detect when the supply 110 is empty. At the channel 112 or 108, a flow sensor may be employed to detect when there is no fluidic flow, even though the pump 106 is running. At the pump 106, a dry running sensor may be employed to detect that the pump 106 is not actively moving fluid from the fluid supply 110 to the reservoir 102.

[0029] When the starter fluid supply 110 is empty, the number of revolutions that the pump 106 rotated to empty the fluid 116 into the reservoir 102 form the starter fluid supply 110 is recorded (214). The value of the fluid level gauge sensor is also sampled (216), and corresponds to both the number of pump revolutions recorded in part 214 and thus the volume of the fluid 116 be the known volume of the starter fluid supply 110 (prior to the fluid thereof being pumped into the reservoir 102). The displacement of the supply pump 106 can be computed as the known volume of the starter fluid supply 110 divided by the number of revolutions to empty this volume of fluid into the reservoir 102, as recorded in part 214. This pump displacement is the volume of fluid that the pump 106 can move from the channel 112 to the channel 108 in one revolution.

[0030] The supply pump 106 and the fluid level gauge sensor 104 can thus be cross-calibrated (220). Cross-calibration of the pump 106 and the fluid level gauge sensor 104 in this respect can include correlating the number or revolutions that it takes for the pump 106 to empty the known volume of a starter or calibration fluid supply 110 into the reservoir 102 with the resulting value of the sensor 104 when the reservoir 102 contains this volume of fluid 116. If the fluid level gauge sensor 104 is linear, then dividing by the latter by the former is indicative of the increase in value of the sensor 104 each time the pump 106 completes one rotation.

[0031] The fluid level gauge sensor 104 may not have to be linear, however, which means that as the level of the fluid 116 in the reservoir 102 linearly increases, the sampled value of the sensor 104 does not linearly increase. In this case, in the implementation in which the value of the fluid level gauge sensor 104 is sampled at different specified numbers of revolutions as the pump 106 empties the fluid supply 110 into the reservoir 102, a non-linear profile of the sensor value by number of pump rotations can be constructed. For instance, a non-linear function can be fitted to the values sampled in part 210 at the specified numbers of pump revolutions and to the value sampled in part 216 corresponding to the number of pump revolutions recorded in part 214.

[0032] FIG. 3 shows an example method 300 for subsequently refilling the reservoir 102 after the supply pump 106 and the fluid level gauge sensor 104 have been cross-calibrated. The method 300 can, like the method 200, be implemented as instructions or other program code stored on a non- transitory computer-readable data storage medium and executed by the fluid- ejection device 100. For instance, a processor other hardware logic of the device 100 can perform the method 300.

[0033] The method 300 begins after the fluid level gauge sensor 104 has detected that the reservoir 102 is depleted of fluid 116 (302). Depletion of the fluid 116 in this respect can mean that the value of the fluid level gauge sensor 104 is below a lower threshold corresponding to the volume of fluid 116 remaining with the reservoir 102 being below a threshold volume. The reservoir 102 may be empty or near empty, for instance.

[0034] The method 300 also begins when a fluid supply 110 has been connected to the fluid channel 112, and thus to the supply pump 106 (304). In one implementation, when the fluid level gauge sensor 104 indicates that the reservoir 102 is depleted of fluid 116, a user may be notified that the reservoir 102 has to be refilled. At that time, the user may connect the fluid supply 110 to the fluid-ejection device 100, and then initiate refilling of the reservoir 102 from the fluid supply 110.

[0035] In another implementation, refilling may be initiated

automatically, responsive to the fluid level gauge sensor 104 detecting depletion of the fluid 116 within the reservoir 102. If a fluid supply 110 remains or is already connected to the fluid-ejection device 100, refilling may be initiated immediately. If a fluid supply 110 is not yet connected, refilling in this implementation may be initiated as soon as the supply 110 is connected to the fluid-ejection device 100.

[0036] Refilling of the reservoir 102 from the external fluid supply 110 using the supply pump 106 is thus started (306). Starting the refilling of the reservoir 102 includes causing the supply pump 106 to start rotating to pump the fluid 116 into the reservoir 102 from the external fluid supply 110. While the reservoir 102 is being refilled from the fluid supply 110 via the supply pump 106, the volume of fluid 116 refilling the reservoir 102 is monitored (308).

[0037] Monitoring of the fluid 116 refilling the reservoir 102 from the external fluid supply 110 using the supply pump 106 is achieved using both the cross-calibrated supply pump 106 and the cross-calibrated fluid level gauge sensor 104. As to the former, the number of revolutions of the supply pump 106 is monitored (310), whereas as to the latter, the value of the fluid level gauge sensor 104 is monitored (312). The number of revolutions of the pump 106 is indicative of the amount of fluid that the pump 106 is pumping from the fluid supply 110 into the reservoir 102. The value of the fluid level gauge sensor 104 is indicative of the level (and thus the volume) of the fluid 116 within the reservoir 102. The refilling of the reservoir 102 is thus separately and independently monitored by each of the supply pump 106 (specifically its number of revolutions) and the fluid level gauge sensor 104 (specifically its sampled value). [0038] Wear and/or malfunction of the supply pump 106 may be detected during refilling of the reservoir 102 via this dual-approached monitoring of the refilling process (314). For instance, as the monitored number of revolutions of the supply pump 106 increases during the refilling process, the monitored value of the fluid level gauge sensor 104 may change less than expected. That is, because the supply pump 106 and the fluid level gauge sensor 104 have been cross-calibrated, the pump 106 is expected to pump a known amount of fluid for each revolution, and the sensor 104 is expected to change in value for an increase of this amount of fluid 116 in the reservoir 102.

[0039] If the sensor 104 does not change as much as expected, however, then this can mean that the pump 106 is moving less fluid from the fluid supply 110 to the reservoir 102 than it should. The supply pump 106 may be suffering from too much wear, or may be malfunctioning. Therefore, refilling of the reservoir 102 may be stopped (320), by stopping rotation of the supply pump 106. An error can be reported to alert the user to such potential wear or malfunctioning of the supply pump 106 (322).

[0040] Assuming no wear or malfunctioning is detected during the refilling process, refilling of the reservoir 102 from the fluid supply 110 via the supply pump 106 continues until the monitored volume of the fluid 116 refilling the reservoir 102 has reached a specified volume. That is, if the number of revolutions of the supply pump 106 has reached a number corresponding to the pump 106 having transferred this specified fluid volume, and/or if the sampled value of the fluid level gauge sensor 104 has reached an upper threshold corresponding to the fluid 116 within the reservoir 102 having this specified volume (316), then refilling is stopped (318). As noted above, the refilling process is stopped by stopping rotation of the supply pump 106.

[0041] Whether the reservoir 102 has been refilled with the specified volume of the fluid 116 is thus tested separately and independently by each of the supply pump 106 and the fluid level gauge sensor 104. If either or both the pump 106 and the sensor 104 indicate that the reservoir 102 has been refilled with this specified fluid volume, then the refilling process stops. For instance, the number of revolutions of the supply pump 106 may indicate that the specified fluid volume has been pumped into the reservoir 102, in which case refilling stops even if the fluid level gauge sensor 104 does not have a value corresponding to the reservoir 102 storing this specified volume of fluid 116. Similarly, the fluid level gauge sensor 104 may indicate that the reservoir 102 now stores the specified volume of fluid 116, in which case refilling stops even if the number of revolutions of the pump 106 does not indicate that the specified fluid volume has been pumped into the reservoir 102.

[0042] Therefore, the refilling process is redundantly monitored. A failure in one monitoring approach does not result in overfilling of the reservoir 102 with fluid if the other monitoring approach signals that the refilling process should stop. For example, if the fluid level gauge sensor 104 fails and underreports the level of fluid 116 within the reservoir 102, overfilling can still be avoided because refilling is stopped responsive to the supply pump 106 having rotated a specified number of revolutions.

[0043] Once refilling has been stopped, malfunction of the fluid level gauge sensor 104 and/or buildup within the reservoir 102 may be detected (324). The fluid 116 may have a solid component, such as pigment particles in the case of pigment inks. Over time, the pigment particles may fall out of solution within the inks, and adhere or otherwise build up on the sidewalls of the reservoir 102. The fluid level gauge sensor 104 may thus report a higher value than expected for the amount of fluid 116 transferred into the reservoir 102 as indicated by the number of revolutions of the pump 106. This is because the buildup reduces the available space for the fluid 116 within reservoir 102, such that the corresponding level of fluid 116 is higher. Since the supply pump 106 and the fluid level gauge sensor 104 have been cross- calibrated, the sensor 104 is expected to have a particular value when the number of revolutions of the pump 106 corresponds to a specified volume of fluid having been transferred into the reservoir 102.

[0044] Malfunction of the fluid level gauge sensor 104 and/or buildup within the reservoir 102 may be detected if the value of the sensor 104 after refilling has been completed is different than expected for the number of revolutions of the supply pump 106 that occurred. That is, refilling may have stopped due to the supply pump 106 having rotated a specified number of revolutions. If at that time the fluid level gauge sensor 104 has a value indicating that a greater volume of fluid 116 is actually within the reservoir 102, then the sensor 104 may be malfunctioning, or there may be buildup within the reservoir 102. Therefore, an error can be reported to alert the user to potential malfunction of the sensor 104 or buildup within the reservoir 102 (322). If such malfunction or buildup is not detected, then the method 300 is finished without error (324). [0045] In one implementation, the differences between detecting wear and/or malfunction of the supply pump 106 in part 314 and detecting

malfunction of the fluid level gauge sensor 104 and/or buildup within the reservoir 102 can include the following. First, the former detection occurs while the refilling process is occurring, whereas the latter detection occurs after the refilling process has stopped. Second, wear and/or malfunction of the supply pump 106 can be detected if the value of the fluid level gauge sensor 104 changes less than (e.g., not more than) expected for each revolution of the pump 106, which can indicate that the supply pump 106 is not pumping the expected volume of fluid during each revolution. By comparison, malfunction of the sensor 104 and/or buildup within the reservoir 102 can be detected if the value of the fluid level gauge sensor 104 is higher than (e.g., not less than) expected for the number of revolutions of the supply pump 106 to refill the reservoir 102 with fluid. Thus, in the former case, the value of the sensor 104 is (changing) less than expected, whereas in the latter case, the value is more than expected.

[0046] FIG. 4 shows an example printing device 400. The printing device 400 is an implementation of the fluid-ejection device 100 that has been described, and may be an inkjet-printing device, or another type of printing device that ejects fluid like ink. The printing device 400 may be a standalone printer, for instance, or an all-in-one (AIO) or a multifunction device (MFD) that includes printing functionality in addition to other functionality, such as copying, scanning, faxing, and so on.

[0047] The printing device 400 includes a print engine 418, which is an implementation of the fluid-ejection engine 118 that has been described. The print engine 418 outputs fluid, such as ink, onto print media like paper. The print engine 418 can thus form images on the print media using the fluid. The printing device 400 includes a reservoir 402, a supply pump 406, and a fluid level gauge sensor 404, which respectively correspond to the reservoir 102, the supply pump 106, and the fluid level gauge sensor 104 that have been described. The printing device 400 includes a pump revolution sensor 422, such as an encoder or another type of sensor, which can indicate when the pump 406 has completed a revolution.

[0048] The printing device 400 includes hardware logic 424. The hardware logic 424 includes a non-transitory computer-readable data storage medium that stores program code. For instance, the hardware logic 424 can include a general purpose processor that executes the program code, or can include special purpose hardware, like an application-specific

integrated circuit (ASIC), which effectuates the program code. The hardware logic 424 can perform the methods 200 and 300 of FIGs. 2 and 3 that have been described. As such, the hardware logic 424 can cross-calibrate the supply pump 406 and the fluid level gauge sensor 404, and subsequently monitor refilling of the reservoir 402.

[0049] The techniques that have been described provide redundancy in monitoring refilling a reservoir of a fluid-ejection device. The redundancy is achieved via both a supply pump of the device and a fluid level gauge sensor of the device that have been cross-calibrated being used to monitor refilling. Therefore, overfilling is less likely to occur. Furthermore, because the pump and the sensor have been cross-calibrated, malfunction and wear of the pump and the sensor can be detected or otherwise predicted.