Measuring magnetic debris buildup in a magnetic filter

Abstract

A magnetic debris level measuring device for a magnetic filter is disclosed. The magnetic debris level measuring device includes a magnetometer and a temperature sensor. The temperature measured by the temperature sensor is used to calculate a corrected magnetometer reading, which in turn can be used to determine the amount of captured magnetic debris held within the filter. The device has a stored threshold for the corrected magnetometer reading, and when the corrected magnetometer reading crosses the stored threshold a notification is issued that the filter is full. If it is detected that debris continues to be captured after the full notification has been issued, the stored threshold will be updated accordingly.

Claims

1. A captured debris level measuring device for a magnetic filter in a central heating system, the captured debris measuring device comprising: a magnetometer for mounting to the magnetic filter to measure a magnetic field strength due to a magnet and any captured magnetic debris; a temperature sensor for mounting to the magnetic filter; and a control unit, the magnetometer and temperature sensor being connected to inputs of the control unit, and output means being provided adapted to issue a notification based on a combination of the magnetometer reading and the temperature sensor reading to provide an indication when the amount of debris captured within the filter exceeds a threshold level, the control unit being adapted to use a reading from the temperature sensor in making a determination as to the amount of magnetic debris captured only when the temperature sensor reading has not changed by more than a predetermined temperature for a predetermined time.

2. The captured debris level measuring device of claim 1, wherein the control unit is adapted to issue a notification based on a magnetometer reading exceeding or dropping below a stored threshold when the temperature sensor reading is within a predetermined range.

3. The captured debris level measuring device of claim 1, wherein the control unit is adapted to combine a temperature reading from the temperature sensor with a raw magnetic field strength reading from the magnetometer to derive a corrected magnetic field strength.

4. The captured debris level measuring device of claim 3, wherein the control unit is adapted to calculate a corrected magnetic field strength y.sub.c
y.sub.c=(y.sub.0t.sup.x)+C where y.sub.0 is the raw magnetometer reading taken from the magnetometer, t is the temperature measured by the temperature sensor, x is a correction exponent and C is a constant.

5. The captured debris level measuring device of claim 4, wherein the correction exponent x is determined according to $x=\frac{\log \left(t_1-t_2\right)}{\log \left(y_1-y_2\right)}$ where y.sub.1 is the magnetometer reading at temperature t.sub.1 and y.sub.2 the magnetometer reading at temperature t.sub.2, where y.sub.1, t.sub.1, y.sub.2, t.sub.2 are obtained experimentally for a constant amount of magnetic debris within the filter.

6. The captured debris level measuring device of claim 3, wherein the control unit is adapted to compare the corrected magnetic field strength to a stored threshold level, the notification being issued when the corrected magnetometer reading exceeds or drops below the stored threshold level.

7. The captured debris level measuring device of claim 6, wherein the control unit is adapted to detect when the amount of magnetic debris captured continues to increase after the stored threshold level has been crossed, and to update the stored threshold level accordingly.

8. A captured debris level measuring device for a magnetic filter in a central heating system, the captured debris measuring device comprising: a magnetometer for mounting to the magnetic filter to measure a magnetic field strength due to a magnet and any captured magnetic debris; a temperature sensor for mounting to the magnetic filter; and a control unit, the magnetometer and temperature sensor being connected to inputs of the control unit, and output means being provided adapted to issue a notification based on a combination of the magnetometer reading and the temperature sensor reading to provide an indication when the amount of debris captured within the filter exceeds a threshold level, the control unit being adapted to combine a temperature reading from the temperature sensor with a raw magnetic field strength reading from the magnetometer to calculate a corrected magnetic field strength y.sub.c, as
y.sub.c=(y.sub.0t.sup.x)+C where y.sub.0 is the raw magnetometer reading taken from the magnetometer, t is the temperature measured by the temperature sensor, x is a correction exponent and C is a constant.

9. The captured debris level measuring device of claim 8, wherein the correction exponent x is determined according to $x=\frac{\log \left(t_1-t_2\right)}{\log \left(y_1-y_2\right)}$ where y.sub.1 is the magnetometer reading at temperature t.sub.1 and y.sub.2 is the magnetometer reading at temperature t.sub.2, where y.sub.1, t.sub.1, y.sub.2, t.sub.2 are obtained experimentally for a constant amount of magnetic debris within the filter.

10. The captured debris level measuring device of claim 8, wherein the control unit is adapted to compare the corrected magnetic field strength to a stored threshold level, the notification being issued when the corrected magnetometer reading exceeds or drops below the stored threshold level.

11. The captured debris level measuring device of claim 10, wherein the control unit is adapted to detect when the amount of magnetic debris captured continues to increase after the stored threshold level has been crossed, and to update the stored threshold level accordingly.

12. The captured debris level measuring device of claim 8, wherein the control unit includes data transmission means adapted to transmit measured magnetic field strength data to a central server.

13. The captured debris level measuring device of claim 1, wherein the control unit includes data transmission means adapted to transmit measured magnetic field strength data to a central server.

Description

DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the invention, and to show more clearly how it may be carried into effect, a preferred embodiment will now be described with reference to the accompanying drawings, in which:

(2) FIG. 1 is a perspective view of a captured debris level measuring device according to first and third aspects of the invention;

(3) FIG. 2 is a rear plan view of the captured debris level measuring device of FIG. 1;

(4) FIG. 3 is a perspective view of the captured debris level measuring device of FIG. 1, shown together with a magnetic filter; and

(5) FIG. 4 is a perspective view of the captured debris level measuring device and filter of FIG. 3, with the captured debris level measuring device installed on the filter.

DESCRIPTION OF THE EMBODIMENTS

(6) Referring firstly to FIGS. 1 and 2, a captured debris level measuring device is indicated generally at 10. The level measuring device is designed to be fitted to a magnetic filter, with the back of the level measuring device (FIG. 2) against a wall of the filter. The level measuring device 10 is fitted to the filter in this case by means of screws. Two screws are provided through counterbored apertures 12 near the top of the device 10. Two further screw fixings are provided through apertures 14 near the bottom of the device 10. In FIG. 1 the fronts of these apertures (14) are obscured by a battery compartment cover 16.

(7) The device 10 is fixed semi-permanently to the magnetic filter in use, so that the device 10 will not move in relation to the filter. The level measuring device 10 contains a three-axis magnetometer (not visible in the figures as it is within the housing of the device 10). The three-axis magnetometer is fixed in position within the housing of the device 10, and so when the device 10 is fixed to the magnetic filter in use, the three-axis magnetometer will be in a fixed position and orientation in relation to the magnet within the magnetic filter.

(8) A temperature sensor 18 protrudes from the back of the housing of the level measuring device 10. Preferably, the temperature sensor 18 is provided mounted on a leaf spring, one end of the leaf spring being fixed relative to the housing of the device 10 and the other free end being movable towards the housing of the device 10 against the action of the spring. Therefore, when the device 10 is fixed to a magnetic filter with the back of the device abutting the exterior wall of the magnetic filter, the temperature sensor 18 on the free end of the leaf spring will be pressed against the exterior wall of the magnetic filter. The temperature sensor is therefore mounted in the best position to measure the temperature of the filter, whilst still being outside the filter and therefore protected from water damage. Mounting the temperature sensor on a spring in this way also allows for simple and effective retrofitting of the level measuring device to an existing magnetic filter.

(9) In FIG. 1, the user interface to the level measuring device is apparent in the form of five LEDs 20a, b, c, d, e and a pushbutton 22. Embodiments may also include data communication means such as NFC, Bluetooth, etc. for providing a more advanced interface and data exchange capabilities.

(10) In operation, the first four LEDS 20a, b, c, d (green in this embodiment) indicate the detected level of magnetic debris captured in the filter. When the captured debris is detected at between 0-25% of capacity, only the first LED 20a will light. When the captured debris is between 25-50%, the first two LEDs 20a, b will light. When the captured debris is between 50-75%, the first three LEDs 20a, b, c will light. When the captured debris is between 75-100%, the first four LEDs 20a, b, c, d will light. The fifth LED 20e is a battery low indicator.

(11) In order to conserve power, in normal circumstances no LEDs will be illuminated. Only when the momentary pushbutton 22 is pressed will the appropriate LEDs be illuminated to show the level of magnetic debris captured and the battery status.

(12) A further pushbutton 24 is located towards the bottom of the device. This pushbutton 24 is a reset button. The button is small and located within a recess in the housing, and so is designed to be difficult to push by mistake. When the filter is serviced the reset pushbutton 24 should be pressed to calibrate the device 10, i.e. pressing the reset pushbutton 24 causes the controller to store the current magnetometer reading (or corrected magnetometer reading) as indicating an empty filter. Where a corrected magnetometer reading is defined as y.sub.c=(y.sub.0t.sup.x)+C in the way described above, storing a zero offset is equivalent to updating the value for C.

(13) Referring now to FIGS. 3 and 4, it is apparent how the level measuring device 10 is fixed onto a magnetic filter 100. Bosses 102 (just one is visible in the perspective of FIG. 3) are provided on the outer wall of the housing of the filter, in positions corresponding to the screw apertures 12 of the level measuring device 10. The temperature sensor 18 mounted on a leaf spring is pressed against the outer wall of the filter 100 when the level measuring device 10 is fixed onto the filter 100.

(14) In use, the temperature sensor (18) and the magnetometer measure respectively the temperature of the exterior wall of the filter 100 and the magnetic field strength at a fixed point just outside the filter 100. Because of the thermal insulation provided by the filter wall, the temperature measured by the temperature sensor 18 will lag the flow temperature of the heating system, for example by a few minutes. However, if there has not been any significant change in the temperature measured for a period of time, for example no change of more than 1 C. within a period of 1 minute, then it can be assumed that the temperature measured by the sensor 18 closely approximates the flow temperature of the heating system, which in turn will closely approximate the temperature of the magnet within the filter. The temperature measured by the temperature sensor and the raw magnetic field strength measured by the magnetometer can therefore be used to calculate a corrected magnetic field strength in the manner described above. The magnetic field strength can then be scaled to derive an indication of the amount of magnetic debris within the filter, for example on a scale of 0 (empty) to 100 (full). The amount of debris can then be output, for example using the LEDs as described above, or communicated to a server by wired or wireless communication means.

(15) Scaling the corrected magnetic field strength involves the use of two stored reference valuesan empty reference value and a full reference value. The full reference value is stored as an offset from the empty reference value. The empty reference value is stored as the current value of the corrected magnetometer reading when the reset pushbutton 24 is pressed. Alternatively setting the empty reference value could be implemented as setting a value for the constant C. The full reference value is set on manufacture to a fairly low value, i.e. to a value which given the variance in magnets and also the types of dirt collected, will in most cases be reached before the magnetic filter is in fact completely full. However, the control unit is configured to detect when the amount of captured debris continues to increase after the full reference value has been reached, and if the amount of captured debris does increase then the stored full reference value can be updated accordingly. In this way, for a particular filter installed in a particular system, over time the control unit will learn when the filter is really full up, and cleaning of the filter can be reduced to the minimum amount necessary to ensure continuous capture of magnetic debris. Apart from saving labour, this has the advantage that the threads, seals etc. on the filter are less susceptible to damage since the filter will have to be disassembled less often.

(16) It will be appreciated that the preferred embodiment is provided as an example of how the inventions may be incorporated into a product. Different features described may be provided in different combinations. The invention is defined by the claims.