SE545681C2

SE545681C2 - Automatic fan control

Info

Publication number: SE545681C2
Application number: SE2051135A
Authority: SE
Inventors: Mikael Klockseth
Original assignee: Tiki Safety Ab
Priority date: 2020-09-30
Filing date: 2020-09-30
Publication date: 2023-12-05
Also published as: SE2051135A1

Abstract

AUTOMATIC FAN CONTROLThe present disclosure relates to a method of controlling fan speed in a respirator (to), and a respirator (to) performing the method.In an aspect, a method of a respirator (to) of controlling speed of a fan (15) configured to draw air inside a mask (11) of the respirator (10) via a filter (12b) is provided. The method comprises measuring (S101) a level of pressure inside the mask (11) being fitted to the face of a user (20) of the respirator (10), controlling (S102) the speed of the fan (15) to create an air flow through the filter (12b) such that a target pressure level is attained inside the mask (11), and recording (S103) the fan speed over a time period, wherein a measure of total volume of air having passed through the filter (12b) during the time period can be determined.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method of controlling fan speed in a respirator, and a respirator performing the method.

BACKGROUND

[0002] In challenging and health-hazardous environments where protection against airborne pollutants (such as e.g. particles and bacteria) is crucial, a protective respirator in the form of a ventilated mask fitted over the face of a user is commonly used.

[0003] These are used for instance in the construction sector to protect against dust, fumes and radium emanation, by relief workers for protection against viruses, in pharmaceutical industry laboratories, etc.

[0004] In these protective respirators, a fan or blower draws air into the mask via a filter. Thus, ambient polluted air is drawn into the fan and purified as it passes through the filter, which purified air is inhaled by the user. Excess air exits the mask via an air outlet.

[0005] Now, a used filter must occasionally be exchanged for a fresh new filter in order to maintain protective capacity of the respirator. The lifetime of a filter depends on numerous parameters, such as the particular environment in which the filter is used, breathing rate of the user of the mask, type of filter, etc.

[0006] As an example, for a physically fit user having a low breathing rate, a filter may last for, say, four full days of use before the filter must be changed for a new filter. For a less physically fit user on the other hand, the filter may have to be changed after a single day of use. Similarly, in a physically demanding environment, which typically requires the user to breathe heavier, the filter generally has a shorter lifetime.

[0007] As is understood, for a group of users being exposed to the same environment, for instance a building construction site, the filters must be changed based on the shortest-lifetime filter of the group of users. In other words, even though one or more of the users potentially could have used a filter for, say, a couple of days, the filters may for safety reasons still need to be changed every day, which is undesirable for reasons of both sustainability and economy.

SUMMARY

[0008] An object is to solve, or at least mitigate this problem in the art and thus to provide an improved respirator configured to control speed of a fan drawing air inside a mask of the respirator via a filter.

[0009] This object is attained in a first aspect by a method of a respirator of controlling speed of a fan configured to draw air inside a mask of the respirator via a filter according to claim

[0010] This object is attained in a second aspect by a respirator comprising a mask, a filter and a fan configured to draw air inside the mask of the respirator via the filter according to claim

[0011] When a user attaches the mask to her face and starts the fan (by a simple keypress), the controller will send a control signal to a fan motor to start rotating the fan in order to create an airﬂow through the filter and the fan for supplying purified air for the user to inhale, the controller will continuously measure the pressure inside and outside the mask using the pressure sensor.

[0012] The controller controls the fan motor such that the fan causes a sufficiently great air ﬂow in order to maintain a positive pressure is inside the mask. Should the pressure inside the mask fall, for instance due to heavy breathing of the user, the controller will control the fan motor to further increase the fan speed such that a positive pressure is maintained inside the mask.

[0013] Finally, the controller records the fan speed to which the fan has been set during a time period. When the user ends her respirator session, the recorded fan speed may advantageously be utilized for determining a measure of total volume of air having ﬂown through the filter during the undertaken session.

[0014] In an embodiment, should the pressure inside the mask fall below zero and thus become negative, the user will be alerted accordingly, for instance by means of an audio alert in the form of a beep, or a visual alert in the form of e.g. a blinking light-emitting diode.[0015] In an embodiment, the controller wirelessly communicates, to the filter being configured for wireless communication, the determined measure of total volume of air having passed through the filter during the time period, for storage at the filter.

[0016] In an embodiment, the controller wirelessly receives, from the filter, information indicating type of the filter being used, the filter type being taken into account upon determining the measure of total volume of air having passed through the filter during the time period.

[0017] In an embodiment, the controller wirelessly communicates the recorded fan speed and time period to a filter maintenance station configured to determine and store the measure of total volume of air having passed through the filter during the time period.

[0018] In an embodiment, the controller maintains the fan speed in case the measured pressure level is at the target pressure level to decrease the pressure inside the mask such that the target pressure is maintained, decreases the fan speed in case the measured pressure level is above the target pressure level to decrease the pressure inside the mask such that the target pressure is attained, and increasing the fan speed in case the measured pressure level is below the target pressure level to increase the pressure inside the mask such that the target pressure is attained.

[0019] In an embodiment, the controller alerts a user of the respirator when a change of the filter is approaching as determined by the determined measure of total volume of air having passed through the filter.

[0020] In an embodiment, the controller alerts the user visually by a display of the respirator indicating remaining lifetime of the filter or by a blinking light source, or the user being alerted audially by a sound.

[0021] In an embodiment, the target pressure level is set to be above 0 mPa, preferably from 0.1 to 0.5 mPa, and most preferably at 0.2 mPa.

[0022] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The stepsof any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Aspects and embodiments are now described, by way of example, with reference to the accompanying drawings, in which:

[0024] Figure 1a illustrates an example of a protective respirator in which embodiments may be implemented;

[0025] Figure 1b illustrates the protective respirator of Figure 1a in an exploded view; [0026] Figure 2 schematic illustrates a filter arranged in a filter housing removably attached to a fan unit according to an embodiment;

[0027] Figure 3 shows a ﬂowchart illustrating an embodiment of a method of controlling fan speed of the respirator of Figure 2;

[0028] Figure 4 shows a ﬂowchart illustrating a method of controlling fan speed of the respirator in an embodiment;

[0029] Figure 5 illustrates the respirator in an embodiment, where a fan unit is equipped with a wireless communication interface;

[0030] Figure 6 illustrates the respirator in an embodiment, where a filter is equipped with a wireless communication interface; and

[0031] Figure 7 illustrates the respirator in another embodiment.

DETAILED DESCRIPTION

[0032] The aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown.

[0033] These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.[0034] Figure 1a illustrates an example protective respirator 10 in which embodiments may be implemented. This is an example only and other respirator designs may be envisaged. Figure 1b shows the respirator 10 in an exploded view.

[0035] The respirator 10 comprises a face mask 11 to be fitted over the face of the user 20. The respirator further comprises a filter unit 12 arranged on top of a fan unit 13 arranged to draw ambient air from the outside to the inside of the mask 11 via the filter unit 12 comprising a filter housing accommodating a filter, which filter separates any pollutants from the air ﬂow and supplies the user 20 with filtered, purified air. Excess air will exit the mask 11 via air outlet 14. As can be seen, the mask 11 may be fitted to the face of the user 20 using straps 30 to avoid any polluted air entering the mask

[0036] For any respirator, users will on an individual basis consume different amounts of air. As a result, for a given time period of respirator usage, the rate of air passing through the fan unit 13 and the filter unit 12 will be different for different users. The lifetime of the filter will thus differ from one user to another.

[0037] As previously mentioned, for a group of users being exposed to the same environment, for instance a building construction site, the filters must in the art be changed based on the individual of the group being the first to have to change filter.

[0038] In a numerical example, assuming that user A consumes 25 litres of air per minute, while user B consumes 100 litres of air per minute due to heavier breathing. If filter specifications stipulate that for the particular environment of the building construction site the filter unit 12 must be changed after 40,000 litres of air has passed through the filter, then it can be concluded that user A will have to change his /her filter after about 26.7 hours of effective use, while user B will have to change the filter after about 6.7 hours of effective use.

[0039] However, for safety reasons, all of the users of the group will have their filters changed after 6-7 hours of use, in practice after every working day in order to avoid any individual of the group using an overdue filter. In other words, even though one or more of the users potentially could have used a filter for four days, the filters must for safety reasons still be changed every day, which is undesirable for reasons of both sustainability and economy.

[0040] This problem is overcome by an embodiment illustrated with reference to the schematic diagram of the filter unit 12 comprising a filter 12b arranged in a filter housing 12a removably attached to the fan unit 13 in Figure 2 and the ﬂowchart of Figure 3 illustrating a method of controlling fan speed of the respirator 10. Further, the filter unit 12 is detachable from the fan unit 13 and thus the mask 11, such that an old filter unit can be changed to a new filter unit.

[0041] As can be seen, an air ﬂow indicated with a dotted line passes through the filter unit 12, being removably attached (for instance via a bayonet socket) to the filter unit 13, and into the mask 11. The polluted air outside the mask 11 is thus purified after having passed the filter 12b for supply to a user of the respirator

[0042] The fan unit 13 comprises fan housing 13a accommodating a fan 15 for causing the air ﬂow, and a fan motor 16 for rotating the fan 15 to create the air ﬂow. The fan unit 13 further comprises a controller 17, such as microprocessor, which controls the fan motor 16 to supply power to the fan 15 in order to speed up/ slow down its rotation and thus increase/ decrease the rate of the airﬂow through the fan and thus the filter 12b.

[0043] The fan unit 13 further comprises a memory 25 storing data and one or more computer programs 24 in the form of e.g. fan control programs executed by the controller

[0044] Further, the fan unit 13 comprises a pressure sensor 18 configured to measure the pressure inside the mask

[0045] Preferably, a sensor which measures relative pressure is used, i.e. a sensor measuring the pressure outside and inside the mask 11. With a relative-pressure measuring sensor, there is no need to calibrate the sensor (unless the respirator is to be used at high altitude); effectively, a relative-pressure measuring sensor measures the inside pressure corrected to ambient, outsides conditions.

[0046] The fan unit 13 further comprises an internally or externally arranged rechargeable battery 19 for powering active components of the fan unit

[0047] Now, the respirator 10 of this embodiment is a positive pressure respirator. In a positive pressure respirator, the air pressure inside the mask 11 is greater than the air pressure outside the mask 11. If the seal between the user”s faceand the mask 11 is not tight, air leaks away from the user”s face, which is highly desirable in case the air carries hazardous fumes or a severe virus such as e.g. Ebola.

[0048] With further refence to the ﬂowchart of Figure 3, when the user attaches the mask 11 to her face and starts the fan (by a simple keypress on the fan unit 13), the controller 17 will send a control signal to the fan motor 16 to start rotating the fan 15 in order to create an airﬂow through the filter unit 12 and the fan 15 for supplying purified air for the user to inhale, the controller 17 will continuously measure the pressure inside and outside the mask 11 using the pressure sensor 18 as illustrated in step S

[0049] The controller 17 will in step S102 control the fan motor 16 such that the fan 15 causes a sufficiently great air ﬂow in order to maintain a positive pressure is inside the mask 11. Should the pressure inside the mask 11 fall, for instance due to heavy breathing of the user, the controller will control the fan motor 16 to further increase the fan speed such that a positive pressure is maintained inside the mask

[0050] In an embodiment, should the pressure inside the mask 11 fall below zero and thus become negative, the user will be alerted accordingly, for instance by means of an audio alert in the form of a beep, or a visual alert in the form of e.g. a blinking light-emitting diode.

[0051] In step S103, the controller 17 records the fan speed to which the fan 15 has been set during a time period. When the user ends her respirator session, the recorded fan speed may advantageously be utilized for determining a measure of total volume of air having ﬂown through the filter unit 12 (and thus the filter 12b) during the undertaken session. It is noted that the fan speed may have changed many times during the session, so the duration for each changing fan speed needs to be recorded.

This will be described in more detail in the following.

[0052] Figure 4 shows a ﬂowchart illustrating a method of controlling fan speed of the respirator 10. In this embodiment, the controller 17 will be programmed to control the speed of the fan 15 such that a target pressure level of e.g. around 0.2 mPa is attained inside the mask 11. Advantageously, a lower (but still positive) pressure inside the mask 11 requires a lower fan speed, which saves energy of the battery 19. It may be envisaged that the target pressure level is set slightly higher, such as at 0.mPa.[0053] If the controller 17 notes that the pressure inside the mask 11 as measured by the pressure sensor 18 in step S101 increases to 0.3 mPa, the controller 17 will control the fan motor 16 to decrease the speed of the fan 15 such that the pressure decreases to the target level of 0.2 mPa, as illustrated in step in step S102b.

[0054] To the contrary, if the controller 17 notes that the pressure inside the mask 11 as measured by the pressure sensor 18 in step S101 decreases to 0.1 mPa, the controller 17 will control the fan motor 16 to increase the speed of the fan such that the pressure increases to the target level of 0.2 mPa, as illustrated in step S102c.

[0055] Should the controller 17 note that the pressure inside the mask 11 as measured by the pressure sensor 18 in step S101 indeed is at the target level of 0.2 mPa, the controller 17 will control the fan motor 16 to maintain the speed of the fan, as illustrated in step in step S102a.

[0056] The controller 17 will further continuously record a current fan speed (or indirectly current consumption of the fan motor 16 which is related to the fan speed) and a time period during which the fan 15 rotates with the current fan speed, as illustrated in step S

[0057] By registering the different fan speeds and the duration of the respective speed, it will subsequently be possible to compute the total ﬂow of air through the fan 15 and thus the filter unit 12 and filter 12b.

[0058] Generally for the fan 15, the following relationship prevails for computing volumetric ﬂowrate G: G EILX/"ï/:zfiaf (equation 1)

[0059] where N is fan speed (typically measured in rotations per minute (rpm)), VFAN is the volume of the fan, which is defined as h x ¶d2 / 4 where h is the height of the fan 15 and d is the diameter of the fan 15. K is a filter-related coefficient and may be expressed as ratio between outside pressure sand inside pressure: Po/ P1. For instance, a thick filter will generally allow a less amount of air to pass through resulting in a greater K, while a thin filter will allow a greater amount of air to pass through resulting in a smaller K. It is noted that equation 1 is a model provided for illustrating purposes and alternative and more complex models can be envisaged for computing the ﬂowrate G.[0060] Thus, in order to compute the total volume of air passing through the filter 12 over a given time period, the controller 17 will also measure the total time for each different speed at which the fan 15 is controlled to rotate. As previously mentioned, a particular current consumption of the motor 16 will correspond to a particular fan speed.

[0061] An exact measure of the total volume of air ﬂowing through the fan 15, and thus the filter 12b, during a time period may thus be attained.

[0062] In an embodiment illustrated with reference to Figure 5, the fan unit 13 and/ or the controller 17 may be provided with a communication interface 21, preferably capable of wireless communication, such as an RFID interface or a Bluetooth interface.

[0063] Upon a user finishing her work shift, she may swipe the fan unit 13 over a filter maintenance station 22 (in the form of e.g. a computer) being located in connection to a store facility where the respirators are kept when not in use, the filter maintenance station 22 also being equipped with an RFID interface for acquiring the measure of the total ﬂow of air having passed through the filter 12b during the work shift.

[0064] Additionally, the filter maintenance station 22 may inform the user of the remaining lifetime of the filter 12b (expecting the same environmental conditions that have prevailed during the work shift just finished).

[0065] It may also be envisaged that the communication interface 21 is capable of long distance wireless communication, in which case the station 22 (being for instance a server) may be remotely located from the respirator

[0066] For instance, with reference to the example hereinabove where the lifetime of the filter under prevailing environmental conditions was expected to expire after 40,000 l of air has passed through the filter; if the fan unit 13 signals to the filter maintenance station 22 that a total of 13,000 l has passed through the filter 12b during the recent work shift, then the user is expected to be capable of performing another two work shifts (amounting to an expected consumption of another 26,000 l to be added to the already consumed 13,000 l) before the filter 12b must be changed to a new one, given that the same filter 12b is used during the next two shifts. It 1O should be noted that when changing the filter 12b, the complete filter unit 12 is typically changed.

[0067] In an embodiment, the respirator 10 may be equipped with a small display, for instance arranged on the fan unit 12, where the total volume of air having passed through the filter 12b is displayed to the user. This number may be updated in real time by the processor 17. Alternatively, the display may show the expected remaining lifetime of the filter 12b, either as an expected time remaining or as the remaining volume of air.

[0068] In a further embodiment, the user may be alerted that the lifetime of the filter 12b is close to expiring, and that the filter 12b needs to be changed, for instance by means of an audio alert in the form of a beep, or a visual alert in the form of e.g. a blinking light-emitting diode.

[0069] Figure 6 illustrates a further embodiment where the filter 12b or the filter unit 12 is equipped with intelligence in the form of a near-field communication (NFC) interface 23, an radio-frequency identification (RFID) interface, or even a Bluetooth interface.

[0070] If the filter 12b or the filter unit 12b is equipped with such wireless communication interface 23, the interface 21 of the fan unit may after a work session communicate the determined total volume of the air having passed through the fan 15 - and thus the filter 12b - during the session for storage in the filter 12b (e.g. in a small memory of the NFC interface 23).

[0071] The filter 12b itself will thus hold information indicating a measure of the total volume of the air having passed through the filter 12b.

[0072] Further, the small memory of the NFC interface 23 may store information identifying filter type.

[0073] As previously discussed, the type of filter used may affect the determined volumetric ﬂowrate G of equation 1. That is, the filter type may affect the air permeability of the filter. For instance, a thick filter will generally allow a less amount of air to pass through, while a thin filter will allow a greater amount of air to pass through, thereby resulting in a varying coefficient K. Further, in the case of using for instance a carbon filter, the rate of the airﬂow should be lower since the air is to passrelatively slow through such a filter. It is thus advantageous that the filter 12b can inform the fan unit 13 (and thus the controller 17) which type of filter it is.

[0074] Hence, providing the filter 12b with the NFC interface 23 will allow the fan unit 13 to communicate a measure of the total volume of air having passed through the filter during a work session, and further allow the filter 12b to communicate information indicating filter type to the fan unit 13 (in practice to the controller 17).

[0075] This will further have the advantage that a filter not necessarily is tied to a particular fan unit. After user A has used a filter, a measure of the total volume of air having passed through the filter 12b is stored in the filter (or the filter unit 12). The filter housing 12a may then be removed from the fan unit 13 and subsequently attached to another filter unit to be used by user B; the filter itself will hold the total volume measure.

[0076] In practice, a user may want to detach the filter housing 12a from the fan unit 13, remove the fan unit 13 from the mask 11, and thereafter clean the mask 11. Without the filter interface 23, the user would have to keep track of the detached filter housing 12a, since the total volume measure for the filter 12b would be held by the controller 17 of the fan unit 13, and not by the filter 12b itself.

[0077] With reference to Figure 7, the steps of the method performed by the respirator 10 of controlling speed of the fan 15 configured to draw air inside the mask 11 of the respirator 10 via the filter 12b according to embodiments are in practice performed by the controller 17 embodied in the form of one or more microprocessors arranged to execute a computer program 24 downloaded to a suitable storage medium 25 associated with the microprocessor, such as a Random Access Memory (RAM), a Flash memory or a hard disk drive. The controller 17 is arranged to cause the respirator 10 to carry out the method according to embodiments when the appropriate computer program 24 comprising computer-executable instructions is downloaded to the storage medium 25, being e.g. a non-transitory storage medium, and executed by the controller 17. The storage medium 25 may also be a computer program product comprising the computer program 24. Alternatively, the computer program 24 may be transferred to the storage medium 25 by means of a suitable computer program product, such as a Digital Versatile Disc (DVD) or a memory stick.

As a further alternative, the computer program 24 may be downloaded to the storage medium 25 over a network. The controller 17 may alternatively be embodied in theform of a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a complex programmable logic device (CPLD), etc.

[0078] The aspects of the present disclosure have mainly been described above with reference to a few embodiments and examples thereof. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

[0079] Thus, while various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

1. Method of a respirator (10) of controlling speed of a fan (15) configured to draw air inside a mask (11) of the respirator (10) via a filter (12b), comprising: measuring (S101) a level of pressure inside the mask (11) being fitted to the face of a user (20) of the respirator (10); controlling (S102) the speed of the fan (15) to create an airﬂow through the filter (12b) such that a target pressure level is attained inside the mask (11); recording (S103) the fan speed over a time period; determining, from the recorded fan speed over the time period, the measure of total volume of air having passed through the filter (12b) during the time period; wirelessly receiving, from the filter (12b) being configured for wireless communication, information indicating type of the filter being used, the filter type being taken into account upon determining the measure of total volume of air having passed through the filter (12b) during the time period; and wirelessly communicating, to the filter (12b), the determined measure of total volume of air having passed through the filter (12b) during the time period, for storage at the filter (12b).

2. The method of any claim 1, further comprising: wirelessly communicating the recorded fan speed and time period to a filter maintenance station (22) configured to determine and store the measure of total volume of air having passed through the filter (12b) during the time period.

3. The method of any one of the preceding claims, wherein the controlling (S102) of the speed of the fan (15) comprises: maintaining (S102a) the fan speed, in case the measured pressure level is at the target pressure level, to decrease the pressure inside the mask (11) such that the target pressure is maintained; decreasing (S102b) the fan speed, in case the measured pressure level is above the target pressure level, to decrease the pressure inside the mask (11) such that the target pressure is attained; and increasing (S102c) the fan speed, in case the measured pressure level is below the target pressure level, to increase the pressure inside the mask (11) such that the target pressure is attained.

4. The method of any one of the preceding claims, further comprising alerting a user (20) of the respirator (10) when a change of the filter (12b) is approaching as determined by the determined measure of total volume of air having passed through the filter (12b).

5. The method of claim 4, the user being alerted visually by a display of the respirator (10) indicating remaining lifetime of the filter (12b) or by a blinking light source, or the user being alerted audially by a sound.

6. The method of any one of the preceding claims, wherein the target pressure level is set to be above o mPa, preferably from 0.1 to 0.5 mPa, and most preferably at 0.2 mPa.

7. The method of any one of the preceding claims, further comprising: alerting a user (20) of the respirator (10) if the pressure inside the mask (11) becomes negative.

8. A respirator (10) comprising a mask (11), a filter (12b) and a fan (15) configured to draw air inside the mask (11) of the respirator (10) via the filter (12b), the respirator further comprising: a pressure sensor (18) configured to measure a level of pressure inside the mask (11) being fitted to the face of a user (20) of the respirator (10); a controller (17) configured to control the speed of the fan (15) to create an airﬂow through the filter (12b) such that a target pressure level is attained inside the mask (11); the controller (17) further being configured to: record the fan speed over a time period; determine, from the recorded fan speed over the time period, the measure of total volume of air having passed through the filter (12b) during the time period; wirelessly receive, from the filter (12b) being configured for wireless communication, information indicating type of the filter being used, the filter type being taken into account upon determining the measure of total volume of air having passed through the filter (12b) during the time period; and to wirelessly communicate, to the filter (12b), the determined measure of total volume of air having passed through the filter (12b) during the time period, for storage at the filter (12b).

9. The respirator (10) of claim 8, the controller (17) further being configured to: wirelessly communicate the recorded fan speed and time period to a filter maintenance station (22) configured to determine and store the measure of total volume of air having passed through the filter (12b) during the time period.

10. The respirator (10) of any one of claims 8-9, the controller (17) further being configured to, when controlling the speed of the fan (15): maintain the fan speed, in case the measured pressure level is at the target pressure level, to decrease the pressure inside the mask (11) such that the target pressure is maintained; decrease the fan speed, in case the measured pressure level is above the target pressure level, to decrease the pressure inside the mask (11) such that the target pressure is attained; and increase the fan speed, in case the measured pressure level is below the target pressure level, to increase the pressure inside the mask (11) such that the target pressure is attained.

11. The respirator (10) of any one of claims 8-10, the controller (17) further being configured to: alert a user (20) of the respirator (10) when a change of the filter (12b) is approaching as determined by the determined measure of total volume of air having passed through the filter (12b).

12. The respirator (10) of claim 11, the controller (17) further being configured to: alert the user visually by a display of the respirator (10) indicating remaining lifetime of the filter (12b) or by a blinking light source, or the user being alerted audially by a sound.

13. The respirator (10) of any one of claims 8-12, wherein the target pressure level is set to be above 0 mPa, preferably from 0.1 to 0.5 mPa, and most preferably at 0.mPa.

14. The respirator (10) of any one of claims 8-13, the controller (17) further being configured to: alert a user (20) of the respirator (10) if the pressure inside the mask (11) becomes negative.

15. A computer program (24) comprising computer-executable instructions for causing a respirator (10) to perform steps recited in any one of claims 1-7 when the computer-executable instructions are executed on a contro11er (17) included in the respirator.

16. A computer program product comprising a computer readab1e medium (25), the computer readab1e medium having the computer program (24) according to c1aimembodied thereon.