Background

[0001 ] A capacitance of circuitry can be used as an indicator a level of fluid in a fluid reservoir. For example, a capacitance may change if a first plate of a capacitor is moved relative to a second plate of a capacitor. If the moving plate is submerged in a liquid, then the change in capacitance will be different to the change in capacitance if the moving plate is in air.

Brief Description of the Drawings

[0002] Examples will now be described, by way of non-limiting example, with reference to the accompanying drawings, in which:

[0003] Figure 1 is a simplified schematic of an example of a replaceable print apparatus component;

[0004] Figure 2 is a simplified schematic of a further example of a replaceable print apparatus component;

[0005] Figure 3 is a simplified schematic of an example of a device for determining a fluid level;

[0006] Figure 4 is a simplified schematic of a further example of a device for determining a fluid level;

[0007] Figure 5 is a simplified schematic of an example of a device mounted to a surface;

[0008] Figure 6 is a simplified schematic of an example of a device and a wall;

[0009] Figure 7 is a series of illustrations showing a device in a fluid container;

[0010] Figure 8 is a flowchart of an example of a method of determining a state of a component;

[001 1 ] Figure 9 is a flowchart of a further example of a method of determining a state of a component; [0012] Figure 10 is a simplified schematic of an example of a print agent container; and

[0013] Figure 1 1 is a simplified schematic of an example of print agent container sensor circuitry.

Detailed Description

[0014] A device is disclosed which can be used to determine a level of fluid in a fluid container. The device, which may be considered to be a fluid level sensor, may be installed into a fluid container, such as a print agent container, which may be used in a printing apparatus. The fluid level sensor may function in such a way that its behaviour inside a fluid container can be examined and analysed from outside the fluid container, without a physical (e.g. wired) connection between the fluid level sensor and a device analysing the sensor's behaviour.

[0015] Figure 1 is a simplified schematic of an example of apparatus for

determining a fluid level. More specifically, Figure 1 is a simplified schematic of an example of a replaceable print apparatus component 100. The component 100 may, in some examples, comprise a print agent container to contain print agent. For example, the component 100 may form at least part of an ink cartridge for use in a printing apparatus.

[0016] The replaceable print apparatus component 100 comprises electrical circuitry 102. The circuitry 102 comprises a first electrically conductive element 104 and a second electrically conductive element 106 capacitively coupled to the first electrically conductive element. A capacitance of the circuitry 102 is variable in response to a stimulus applied to the circuitry. The circuitry 102 may include other electronic components which are not discussed herein. The circuitry 102, may form a part of a fluid level sensor described above. For example, the first electrically conductive element 104 may be located on, or form part of, a fluid level sensor to be disposed within a fluid container, such as the replaceable print apparatus component 100. [0017] In some examples, the first electrically conductive element 104 may be disposed outside the replaceable print apparatus component 100 and the second electrically conductive element 106 may be disposed within the replaceable print apparatus component (as shown in Figure 2). In other examples, the positions of the first and second electrically conductive elements 104, 106 may be reversed (i.e. the second electrically conductive element may be disposed outside the replaceable print apparatus component 100 and the first electrically conductive element may be disposed within the replaceable print apparatus component). The electrically conductive element which is disposed outside the replaceable print apparatus component 100 (e.g. the first electrically conductive element 104) may, for example, be disposed on an outer surface of a wall or housing of the replaceable print apparatus component. In some examples, the first electrically conductive element 104 which is disposed outside the replaceable print apparatus component 100 may be remote from (e.g. spaced apart or separated from) the replaceable print apparatus component. However, the first electrically conductive element 104 outside the replaceable print apparatus component 100 is close enough to the second electrically conductive element to maintain a capacitive coupling between the first and second electrically conductive elements 104, 106. As discussed below the second electrical contact 104 may be movable relative to the first electrical contact 102. In some examples, in order to maintain a capacitive coupling between the electrical contacts, the second electrical contact 104 may, in its resting position, be positioned within approximately 4 millimetres of the first electrical contact 102. Thus, the second electrically conductive element 106 may be in wireless electrical communication with the first electrically conductive 104 element through a wall of the replaceable print apparatus component. In other words, no wires pass through the wall of the replaceable print apparatus component 100.

[0018] Figure 2 is a simplified schematic of a further example of a replaceable print apparatus component 100. According to the example shown in Figure 2, the replaceable print apparatus component 100 may further comprise a third electrically conductive element 202 disposed outside the replaceable print apparatus

component and a fourth electrically conductive element 204 capacitively coupled to the third electrically conductive element, the fourth electrically conductive element being disposed within the replaceable print apparatus component. As in the example discussed above, the third electrically conductive element 202 may, in some examples, be disposed on an outer surface of a wall or housing of the replaceable print apparatus component 100. The third electrically conductive element 202 may be in electrical communication (e.g. capacitively or by a wired connection) with the first electrically conductive element 104, as discussed below.

[0019] In some examples, those electrically conductive elements disposed within the replaceable print apparatus component 100 (e.g. the second and fourth electrically conductive elements 106, 204 in the above examples), may be disposed on or connected to an inner surface of a wall or housing of the replaceable print apparatus component (e.g. the inner surface of the wall or housing on which the first and third electrically conductive elements 104, 202 are disposed).

[0020] The electrically conductive elements 106, 204 disposed within the replaceable print apparatus component 100 may exhibit distinct resonant

behaviours. In some examples, the second electrically conductive element 106 and the fourth electrically conductive element 204 have distinct resonant frequencies. For example, the second electrically conductive element 106 may have a first resonant frequency and the fourth electrically conductive element 204 may have a second resonant frequency which is different to the first resonant frequency. As noted above, the second and fourth electrically conductive elements 106, 204 may form part of a device to function as a fluid level sensor. In some examples, the second and fourth electrically conductive elements 106, 204 may be in electrical communication with one another, for example via circuitry within the replaceable print apparatus component 100. The circuitry may, for example, form part of the device (i.e. the fluid level sensor) itself. The material, size and/or configuration of the device may be selected based on the intended resonant vibrational frequency of the electrically conductive elements. In some examples, the arms 402, 404 may have a resonant vibrational frequency on the order of 10 to 100 Hz. This is within the range of frequencies that may be readily achieved using a stainless steel flat device with dimensions suitable for inclusion in print apparatus, and detection apparatus (for example, analogue to digital converters) which is sensitive to this range is readily available. In some examples, frequencies around national power supply frequencies (for example, around 50 Hz and 60 Hz in most countries) may be avoided, as this can result in a false reading due to the power supply signal.

[0021 ] According to some examples, the first and second electrically conductive elements 104, 106 may be considered to be plates of a variable capacitor. Thus, a fluid level sensor may comprise a variable capacitor having a first electrical member and a second electrical member capacitively coupled to the first electrical member. A capacitance of the variable capacitor may be variable in response to a stimulus applied to the variable capacitor. For example, a stimulus may be applied to one of the electrical members, and this may cause a change in the capacitance of the variable capacitor. The fluid level sensor may be incorporated into, or mounted or otherwise disposed within a fluid container, or a replaceable print apparatus component (e.g. a print agent container).

[0022] An example of a device 300 for sensing a fluid level in a fluid container is shown in Figure 3. In the example shown in Figure 3, the device 300 is generally rectangular. In other examples, however, as is apparent from the examples below, the device may have a different general shape.

[0023] The device 300 may, in some examples, include, a mounting portion 302 for mounting the device to a surface, such as the inner surface of a wall or housing of a fluid container. The device 300 may include an electrically conductive element, such as the second electrically conductive element 106. In some examples, the mounting portion 302 may be located at or near to a first, proximal end of the device 300 and the second electrically conductive element 106 may be located at or near to a second, distal end of the device.

[0024] A further example of a device 400 for sensing a fluid level in a fluid container is shown in Figure 4. In the example shown in Figure 4, the device 400 is generally L-shaped. The device 400 includes a mounting portion 402 for mounting the device to a surface, such as the inner surface of a wall or housing of a fluid container. The mounting portion may include an aperture, or multiple apertures 404, for receiving a peg, screw or the like, for attaching the device to a surface. The device 400 includes two electrically conductive elements, corresponding to the elements 106, 204 shown in Figure 2. In the arrangement of Figure 4, however, each element is positioned on a limb, or arm. For example, the second electrically conductive element 106 may be located on a first arm 406 and the fourth electrically conductive element 204 may be located on a second arm 408. In some examples, the mounting portion 402 may be located at a portion of the device from which the first arm 406 and the second arm 408 extend. In general, the arrangement of the device 400 may be such that, in use, the electrically conductive elements 106 and 204 are disposed at different depths within a fluid container.

[0025] In other examples, the device may be of a shape and/or configuration other than those shown in Figures 3 and 4. In general, the device 300, 400 may be formed from any material which allows suitable vibration characteristics to be designed. In other words, any material may be used which exhibits a strong vibratory response to a stimulus. Using a metal may further enable an electrical connection to be formed through the device. In some examples, the device 300, 400 may be formed from 301/302 stainless steel. Such a material has strong chemical resistance characteristics. A ferritic material, such as ferritic steel allows for magnetic excitation of the device, as discussed below.

[0026] Figure 5 is a simplified schematic of an example of a device, such as the device 300, mounted to a surface, such as surface 502 of a wall 504 of a fluid container. The device 300 is mounted to the wall 504 at the mounting portion 302. The device 300, in this example, is substantially planar. The device 300 may, for example, be formed from sheet metal, such as aluminium, stainless steel, or the like. The second electrically conductive element 106 is located at the distal end of the device 300, and is spaced apart from the wall 504. The distal end of the device 300, including the second electrically conductive element 106, is moveable relative to the wall 504. In this way, the second electrically conductive element 106 may move in a direction shown by the arrow A, for example in a vibratory manner, when a stimulus is applied to the device 300. Thus, in some examples, the second electrically conductive element may comprise a vibrational element. Various methods of applying a stimulus to the device 300 are discussed herein. In general, however, the stimulus is to cause the second electrically conductive element 106 to move relative to the wall 504 (e.g. oscillate towards and away from the wall).

[0027] Electrically conductive elements are provided on an outer surface 506 of the wall 504. In the example shown in Figure 5, the first electrically conductive element 104 is provided at a position substantially aligned with the second electrically conductive element 106 of the device 300. In this way, the first and second electrically conductive elements 104, 106 are capacitively coupled to one another through the wall 504 and through a gap between the wall and the second electrical contact. The proximal end of the device 300 is in electrical communication with an electrical contact 508 formed on the outer surface 506 of the wall 504. In some examples, the proximal end (e.g. the mounting portion 302) of the device may be capacitively coupled to the electrical contact 508, as indicated in Figure 5. In other examples, a physical electrical connection may exist between the electrical contact 508 and the proximal end of the device 300, for example via mounting elements used to mount the device 300 to the wall 504.

[0028] The first electrically conductive element 104 and the electrical contact 508 may be electrically connected, for example capacitively or physically, with other components or circuitry 510. The circuitry 510 may include processing circuitry, for example for measuring capacitances. In some examples, an air gap and an associated capacitance may be introduced between the electrical contact 508 and the circuitry 510, and between the first electrically conductive element 102 and the circuitry 510. In some examples, the fluid container may comprise a print agent container, such as an ink cartridge. The ink cartridge may be mounted in a carriage to move the ink cartridge over a substrate to be printed. The first electrically conductive element 104 and the electrical contact 508 may be electrically connected to electrical contacts of the carriage and/or to circuitry associated with a printing apparatus.

[0029] A stimulus may be applied to the second electrically conductive element 106, to the device 300 and/or to the replaceable print apparatus component 100. In some examples, a stimulus may comprise an impulse applied to the conductive element 106, the device 300 and/or the component 100. For example, an impulse (e.g. a sudden impact, or brief force) may be applied by causing the carriage carrying the ink cartridge to knock against a surface. In other examples, a stimulus may comprise an electromagnetic pulse, acoustic pulse (e.g. an acoustic radiation force, such as a low frequency vibration, generated by a woofer) or some other force applied to the conductive element 106, the device 300 and/or the component 100. For example, a magnetic field may be generated for a short period of time, in order to attract the distal end of the device 300 in a direction away from the wall 504.

Once the magnetic field is deactivated, the distal end (i.e. the end at which the second electrically conductive element 106 is located) is released from the magnetic attraction, causing it to return to its original, resting, position. The magnetic field may be generated by a device located remote to the fluid container, for example a magnet, or an electromagnet located in the printing apparatus.

[0030] After a stimulus (in any form) has been applied to the second electrically conductive element 106 of the device, the distal end of the device may undergo oscillatory motion as it returns to its resting position. In other words, the second electrically conductive element 106 may oscillate towards and away from the wall 504 in the direction of the arrow A in Figure 5, for example in a vibratory manner. As such, the portion of the device capable of moving relative to the wall 504 may be considered to be a vibrational member.

[0031 ] The example shown in Figure 5 relates to a device 300 having a single vibrational member (i.e. the second electrically conductive element 106). In other examples, the device may include additional vibrational members which may move (e.g. with oscillatory motion) relative to a wall of the fluid container in which the device is located. For example, the device 400 shown in Figure 4 has two vibrational members, namely the second electrically conductive element 106 located on the first arm 406, and the fourth electrically conductive element 204 located on the second arm 408. Proximal ends of the first and second arms 406, 408 may be connected to the wall of fluid container, and the distal ends of the arms may be free to move relative to the wall, for example in the manner described above with reference to Figure 5. In other examples, the device may include more or fewer vibrational members. For example, a device may include one, two, three, four or five or more vibrational members. Each vibrational member may be in electrical capacitive communication with a corresponding electrically conductive element located outside the wall 504 of the replaceable print apparatus component.

[0032] Figure 6 is a simplified schematic showing an example of the device 400 and a wall 504 of a fluid container. The position of the device 400 in its mounted position on the wall is shown by the outline 602 and dashed lines indicate the positions of the conductive elements 106, 204 when the device is mounted on the wall 504 of the fluid container. The positions of the first electrically conductive element 104 and the third electrically conductive element 202 on the outer surface of the wall 504 are indicated. The circuitry 510 to which the electrically conductive elements 104, 202 may be connected is also shown. In this example, the mounting portion 402 of the device 400 may not form a direct electrical connection with a contact (e.g. electrical contact 508) formed on the outer surface of the wall 504 in a position aligned with the mounting portion. Instead, a capacitive connection is formed between the first electrically conductive element 104 outside the fluid container and the second electrically conductive element 106 of the device 400 (through the wall 504). A capacitive connection is also formed between the third electrically conductive element 202 outside the fluid container and the fourth electrically conductive element 204 of the device 400 (through the wall 504). The first electrically conductive element 104 and the third electrically conductive element 202 may be electrically connected, for example capacitively or physically, with other components or circuitry, such as circuitry 510.

[0033] As noted above, when a stimulus is applied to the device 300, 400 or to a fluid container in which the device is disposed, the free end or ends (i.e. the second electrically conductive element 106 and/or the fourth electrically conductive element 204) may be caused to oscillate or vibrate relative to the wall 504. As the electrically conductive element 106, 204 move relative to the wall 504 (and, therefore, relative to the first and third electrically conductive elements 104, 202 outside the fluid container), the capacitance of the circuitry, and particularly of each capacitive coupling, is caused to vary. By measuring the variation in the capacitance resulting from the movement of the electrically conductive elements 106, 204, it is possible to determine whether each of the electrically conductive elements is submerged in a substance in the fluid container. If the electrically conductive elements 106, 204 are caused to vibrate in air, then they will vibrate at their resonant frequency. However, if the electrically conductive elements 106, 204 are submerged in a substance, such as print agent, then they will not vibrate at their resonant frequency, or they will vibrate, but with heavy damping. Thus, if the capacitance changes at a rate corresponding to the resonant frequency of a particular electrically conductive element 106, 204, then it may be determined that the electrically conductive element is oscillating in air and, therefore, is not submerged in a liquid, such as print agent.

[0034] Movement of the electrically conductive elements 106, 204 or, more generally, of the arms of the device 300, 400, may be caused in various ways. In some examples, as discussed above, an impulse may be applied to the device 300, 400 or to the fluid container 100. An impulse may be considered to be a momentary force which causes the free ends of the arms of the device 300, 400 to oscillate or vibrate. By measuring the change in capacitance immediately after (or soon after) the impulse has been applied, it may be possible to determine whether either of the arms (and, therefore, either of the electrically conductive elements 106, 204) is vibrating at its resonant frequency.

[0035] In some examples, an impulse, or sudden force, may be applied by causing a moving fluid container containing the device 300, 400 to rapidly decelerate, for example by stopping a carriage housing the fluid container suddenly, or by causing the carriage to knock against a stopping member. As described above, an external device, such as an electromagnet, may be used to generate an impulse force, by generating a magnetic field to act on the free arm or arms of the device 300, 400, then removing the magnetic field, to cause the free arm or arms to oscillate as they return to a resting position.

[0036] Another way of causing movement of the arms of the device 300, 400 is to cause movement of the arms at a defined driving frequency. In some examples, a direction of movement of the fluid container may rapidly and repeatedly be reversed. Such movement may be referred to as cyclic movement. For example, a mechanism for causing a carriage to move within a printing apparatus may cause the fluid container to move backwards and forwards, for example along a track, at a defined frequency. Fluid, such as print agent, within the fluid container 100 may be caused to slosh from one side of the fluid container to an opposite side of the fluid container at the same defined frequency. The moving liquid may cause the free arm or arms of the device to oscillate at the same frequency. During the movement of the device 300, 400, the capacitance of the circuitry may change at a rate corresponding to the driving frequency, and the change in capacitance may be measured, for example by circuitry connected to the device, such as the circuitry 510. If it is determined that a particular arm of the device 300, 400 is vibrating or oscillating at the driving frequency, then it may be determined that the particular arm is submerged, or at least partially submerged, in a liquid.

[0037] In some examples, cyclic movement of the device may be caused using a force generated by an external, such as the electromagnet discussed above or an acoustic wave generator, such as a woofer. For example, an electromagnet may be activated and deactivated at a driving frequency so as to cause a magnetic field to act on the device 300, 400, and therefore cause oscillatory movement of the arm or arms of the device, at the driving frequency.

[0038] Thus, the change in capacitance between the first electrically conductive element and the second electrically conductive element may, in some examples, be indicative of a state of the replaceable print apparatus component. As discussed above, the state may, in some examples, be a level of fluid in the replaceable print apparatus component. Thus, in examples in which the replaceable print apparatus component comprises a print agent container, the change in capacitance between the first electrically conductive element 104 and the second electrically conductive element 106 may be indicative of an amount of print agent in the print agent container. Similarly, the change in capacitance between the third electrically conductive element 202 and the fourth electrically conductive element 204 may be indicative of a state of the replaceable print apparatus component, such as an amount of print agent in a print agent container.

[0039] Figure 7 is a series of illustrations showing an example of how a device such as the device 400 may be used to determine a fluid level in a fluid container 100.

[0040] In the example shown in Figure 7A, the fluid container 100 is substantially full of fluid, such as print agent 702. The fluid container 100 of Figure 7A is representative of a print agent container (e.g. a print agent cartridge) when it newly inserted into a printing system. The fluid 702 covers the second electrically conductive element 106 and partially covers the fourth electrically conductive element 204. After insertion of the print agent container 100 into a printing

apparatus, a cyclic stimulus may be applied to the container causing movement (e.g. sloshing) of the fluid 702 in the container at a defined driving frequency.

[0041 ] If the change in capacitance detected in response to the application of the cyclic stimulus or force indicates a variation at the same driving frequency, then it may be determined that both arms of the device 300, 400 are submerged in the fluid 702 and are, therefore being caused to oscillate as a result of the fluid sloshing within the fluid container 100. From such a response, it may be determined that a device 300, 400 is present within the fluid container 100 and that the fluid container contains an expected amount of fluid (e.g. to confirm that a new print agent container contains the intended amount of print agent). The response may also confirm that the device 300, 400 is functioning as intended (e.g. that the free ends of the arms of the device are able to move and vibrate relative to the wall 504).

[0042] In the scenario shown in the example of Figure 7B, the fluid level has reduced to below the fourth electrically conductive element 204. This fluid level may be detected by applying an impulse stimulus to the device 300, 400. For example, an impulse may be applied to the device 300, 400 at regular intervals. In some examples, processing apparatus associated with the fluid container 100 (e.g. a processor in the printing apparatus) may estimate the amount of print agent remaining in a print agent container based on an amount of print agent deposited from the print agent container during printing tasks that have been performed. For example, an amount of print agent that has been used from the print agent container 100 may be estimated based on a drop size (e.g. an estimated or measured drop size) of print agent as it is deposited from the container, and the number of drops that have been deposited. From such an estimation, it may be possible to predict approximately when the fluid level is to fall below the level of the arm on which the fourth electrically conductive element 204 is located. Thus, in some examples, an impulse may be applied to the device 300, 400 at regular intervals when it is expected that the fluid level is soon to drop below the fourth electrically conductive element 204.

[0043] When the fourth electrically conductive element 204 is above the fluid level (i.e. element is in air rather than submerged in the fluid 702), it will vibrate at its resonant frequency. However, in the scenario shown in Figure 7B, the second electrically conductive element 106 is submerged within the fluid 702 and, therefore, if any oscillations are detected, then they will be at a frequency other than its resonant frequency and/or at the resonant frequency but with heavy damping.

Therefore, by analysing a response to an impulse applied the device 300, 400 in the scenario of Figure 7B, it may be possible to determine that the fluid level is between the level of the fourth electrically conductive element 204 (i.e. the element located on the top arm of the device) and the second electrically conductive element 106 (i.e. the element located on the bottom arm of the device).

[0044] An estimated number of drops deposited from the fluid container 100 between the fluid level shown in Figure 7A (e.g. when the fluid container contains an initial amount of fluid) and the fluid level shown in Figure 7B (i.e. when the fluid level drops below the fourth electrically conductive element 204) can be compared with an actual amount of fluid used between those levels. If the actual amount of fluid used differs from the expected amount of fluid used, then the expected fluid drop size may be recalibrated or adjusted so that the estimated fluid use is more accurate. In some examples, if a response to a stimulus applied to the device 300, 400 indicates that the fluid level has failed to fall to the level shown in Figure 7B (e.g. after a defined amount of usage), then it may be determined that the fluid container or the device 300, 400 is functioning incorrectly. Appropriate action may consequently be taken, such as indicating a potential error to a user, or preventing further use of the fluid container.

[0045] In the scenario shown in the example of Figure 7C, the fluid level has reduced to a level just above the second electrically conductive element 106. A response to an impulse stimulus applied to the device 300, 400 when the fluid level is at the position shown in Figure 7C is likely to be similar to the response measured in the scenario of Figure 7B. The expected drop count may be used to determine an expected time at which the fluid level will fall below the second electrically conductive element 106 of the device 300, 400. In some examples, heavily damped vibrations may be detected in the response, due to the presence of liquid surrounding the electrically conduct (vibrational) elements. Any difference in the degree of damping between the scenarios shown in Figures 7B and 7C may be detected and further used to confirm whether or not a particular element is submerged in liquid. By confirming that the fluid level first falls below the (upper) fourth electrically conductive element 204, and then below the (lower) second electrically conductive element 106, it may be possible to confirm that the print agent container 100 has not been refilled. For example, if the fourth electrically conductive element 204 repeatedly becomes covered and uncovered by print agent, then this might suggest that the print agent container has been connected to an external print agent supply. If such a

determination is made, then appropriate action may be taken, such as indicating a potential error to a user, or preventing further use of the fluid container.

[0046] In the scenario shown in the example of Figure 7D, the fluid level has reduced to below the second electrically conductive element 106. Based on the drop size of fluid to be deposited by the fluid container, it is possible to estimate

approximately when the fluid level will reduce to the level shown in Figure 7D. When it is expected that the fluid level will reduce to below the second electrically conductive element 106, a plurality of impulses may be applied to the device 300, 400 at intervals. Once the fluid level has dropped below the second electrically conductive element 106, the response to an impulse stimulus will indicate that each of the second and fourth electrically conductive elements 106, 204 oscillate or vibrate (at least temporarily) at a corresponding resonant frequency. A detection that the fluid level has dropped to the level shown in Figure 7D may be indicative that the fluid container is near to an "end of life" state, or that the fluid container 100 is nearly out of fluid (e.g. print agent). With such an accurate determination, a user may be accurately informed that the fluid container is nearly empty.

[0047] While the examples of Figure 7 include a device 300, 400 having two arms and two electrically conductive elements, similar measurements and determinations could be made using a device having a single arm, such as the device 300. Multiple devices 300, 400 may be incorporated into a fluid container to obtain a greater number of measurements.

[0048] In the above examples, capacitive sensing is used to measure the response of the device when a stimulus is applied. In other examples, however, inductive sensing may be used instead of capacitive sensing. For example, movement of a magnet attached to the arm or arms of the device may induce a current in an electromagnetic coil. The frequency component of the response may be measured.

[0049] Figure 8 is a flowchart of an example of a method 800 for determining a state of a component. The method 800 comprises, at block 802, applying a stimulus to sensor circuitry associated with a replaceable print apparatus component. The sensor circuitry may comprise an electrically conductive element 104, 106, 202, 204 discussed above. The replaceable print apparatus component may comprise a print agent container, such as an ink cartridge, as discussed in examples described herein. The stimulus may comprise a stimulus such as an impulse force and/or a cyclic force, as discussed herein.

[0050] At block 804, the method 800 may comprise determining a change in a capacitance of the sensor circuitry in response to the stimulus. As discussed herein, the change in capacitance may occur at a frequency corresponding to the resonant frequency of the sensor circuitry, or an element thereof, if the circuitry or the element is excited with a sudden stimulus, such as an impulse force.

[0051 ] The method may comprise, at block 806, determining, based on the measured change in capacitance, a state of the replaceable print apparatus component. In some examples, an amount of fluid in the replaceable print apparatus component may be determined, for example by analysing which elements are caused to vibrate or oscillate at their resonant frequencies (thereby implying that the element is in air rather than in some other substance).

[0052] In some examples, applying a stimulus may comprise one of applying an impulse to the sensor circuitry, causing an impulse to the sensor circuitry through an impact applied to a carriage carrying the replaceable print apparatus component (as discussed above), applying an acoustic pulse to the sensor circuitry and applying an electromagnetic pulse to the sensor circuitry. In other examples, a stimulus or multiple stimuli may be applied comprising an impulse, an acoustic pulse and an electromagnetic pulse. The impulse, acoustic pulse or electromagnetic pulse may be applied using the techniques described herein.

[0053] Determining a change in the capacitance of the sensor circuitry (block 804) may, in some examples, comprise determining one of a change in the capacitance over a defined period and a rate of change in the capacitance over a defined period. For example, the change in capacitance may be measured over a period of 1 second, 2 seconds or 3 seconds. In some examples, the change in capacitance may be determined over a period during which the oscillation of an element of the sensor circuitry exhibits resonant behaviour (e.g. a period sufficient to detect oscillation at a resonant frequency). In other examples, the change in capacitance may be determined over a period sufficient to determine an extent of damping in the oscillation or vibration of an element of the sensor circuitry. In this way, it may be possible to determine whether the element is surrounded by air (in which case the extent of damping of the oscillations may be relatively small) or submerged in a substance (in which case significant damping may be evident). In some examples, a rate of change of the capacitance may be determined over a defined period. In this way, a frequency of the oscillations (e.g. the oscillating capacitance) may be determined over a defined period.

[0054] In some examples, determining a change in the capacitance of the sensor circuitry may comprise measuring an analogue alternating frequency component associated with the sensor circuitry in response to the stimulus. In other words, the sensor circuitry may be caused to communicate an analogue alternative frequency component (e.g. a change in capacitance) to circuitry (e.g. measurement or analysis circuitry) outside the replaceable print apparatus component. The analogue signal may be converted to a digital signal, for example using an analogue-to-digital convertor.

[0055] Figure 9 is a flowchart of an example of a method 900 for determining a state of a component. The method 900 may comprise blocks from Figure 8. The method 900 may, in some examples, comprise indicating the determined state to a user. For example, the determined state may be indicated via a display associated with printing apparatus. The indication may comprise a visual or audible indication, by which the state of the replaceable print apparatus component may be

communicated to a user.

[0056] In some examples, state of the replaceable print apparatus component to be determined may comprise a type or colour of fluid (e.g. print agent) within the component. For example, in a printing apparatus, multiple print agent containers may be used, each container housing print agent of a different colour. In some examples, a printing apparatus may include four print agent containers - cyan (C), magenta (M), yellow (Y) and black (K). Each print agent container may include a device 300, 400. Each device 300, 400 may have an electrically conductive element which has a resonant behaviour (e.g. a resonant frequency) distinct from the elements of the devices of the other print agent containers. In this way, detection of a particular resonant behaviour (e.g. detection of a capacitance varying at a rate corresponding to a particular resonant frequency) may be indicative of the particular container from which the behaviour is detected. Thus, it is possible to discriminate between different print agent containers. This may be used, for example, to determine if a print agent container (e.g. an ink cartridge) containing cyan, magenta or yellow print agent is installed into the position intended for the cartridge containing black print agent.

[0057] In other examples, discrimination between different replaceable print apparatus components, such as print agent containers, may be achieved by positioning or orienting the device, or an arm or arms of the device, differently in different types of print agent container. For example, in a container for yellow print agent, the device may be oriented as shown in Figure 7. In a container for cyan print agent, the device may be rotated through 90 degrees, and so on.

[0058] Figure 10 is a simplified schematic of a print agent container 1000. The print agent container 1000 (e.g. an ink cartridge for a printing apparatus), comprises a housing 1002. The print agent container 1000 comprises circuitry 1004 comprising a first electrical contact 1006 disposed within the housing and a second electrical contact 1008 disposed outside the housing and capacitively coupled to the first electrical contact. A capacitance of the circuitry may be variable in response to movement of the second electrical contact 1008 relative to the first electrical contact 1006. In some examples, the first electrical contact 1006 may comprise, or be similar to, the first electrically conductive element 104. The second electrical contact 1008 may comprise, or be similar to, the second electrically conductive element 106.

[0059] The first and second electrical contacts 1006, 1008 may together function as a variable capacitor. The first electrical contact 1006 may be caused to move by receiving a force or other stimulus, for example using a technique discussed herein. The change in capacitance, and/or a rate of change of capacitance may be indicative of the frequency of oscillation or vibration of the first electrical contact 1006 following excitation by the stimulus (e.g. after a force has been applied to the first electrical contact), which may be used to determine whether or not the first electrical contact submerged in print agent.

[0060] Figure 1 1 is a simplified schematic of an example of print agent container sensor circuitry 1 100. The print agent container sensor circuitry 1 100 is to generate a signal in response to an impulse applied to the print agent container sensor circuitry. The impulse may be applied using a technique as described herein. The circuitry 1 100 may comprise the first and second electrically conductive elements 104, 106 described herein. The circuitry 1 100 may be used to determine a state of the print agent container. For example, the circuitry 1 100 may be used to determine a level of print agent within the print agent container. In some examples, the generated signal may be representative of a change of capacitance of the sensor circuitry 1 100. The change in capacitance may be used to determine the state of the print agent container, as described herein.

[0061 ] The present disclosure is described with reference to flow charts and/or block diagrams of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart.

[0062] While the method, apparatus and related aspects have been described with reference to certain examples, various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the present disclosure. It is intended, therefore, that the method, apparatus and related aspects be limited only by the scope of the following claims and their equivalents. It should be noted that the above-mentioned examples illustrate rather than limit what is described herein, and that those skilled in the art will be able to design many alternative implementations without departing from the scope of the appended claims. Features described in relation to one example may be combined with features of another example.

[0063] The word "comprising" does not exclude the presence of elements other than those listed in a claim, "a" or "an" does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims.

[0064] The features of any dependent claim may be combined with the features of any of the independent claims or other dependent claims.