WO2003037436A1

WO2003037436A1 - Method and apparatus for calibrating air content of a respirator

Info

Publication number: WO2003037436A1
Application number: PCT/FI2002/000845
Authority: WO
Inventors: Juha HIRSIMÄKI
Original assignee: Scott Health and Safety Oy
Current assignee: Scott Health and Safety Oy
Priority date: 2001-11-01
Filing date: 2002-10-31
Publication date: 2003-05-08
Anticipated expiration: 2004-05-01
Also published as: EP1439886A1; FI111606B; FI20012117L; FI20012117A0

Abstract

The invention relates to a method and apparatus for calibrating the amount of air supplied by a blower unit to a respirator. The method according to the invention for calibrating the air flow rate on a respirator blower unit comprises steps in which the blower unit is set in a special calibration mode (207) and there is issued a signal prompting to attach a certain first constant load to the blower unit (208). In response to a certain signal indicating the attachment of a first constant load it is started to change the rate of the air flow produced by the blower unit (209). Furthermore, in response to certain first signal indicating that the desired air flow rate has been reached, it is stopped changing the rate of the air flow produced by the blower unitand saved certain control information (210) describing the operation of the blower unit at that air flow rate at which the changing of the air flow rate was stopped. The control information saved is used for producing such general control information which describes the operation of the blower unit when it produces an air flow at a constant rate.

Description

Method and apparatus for calibrating air content of a respirator

The invention relates to a method and apparatus for calibrating the amount of air supplied by a blower unit to a respirator.

A respirator comprises a blower unit for boosting the intake of air, a face piece in connection therewith, and various filters. The amount of air supplied by the blower unit to the respirator is typically calibrated during the assembly of the apparatus and during maintenance. In practice, calibration is done by a service technician who opens a service lid in the apparatus and trims a potentiometer, for example; or a computer controls the calibration and monitors the variations of the quantities asso- ciated therewith. Calibrating the air supply requires precision and has to fulfil certain norms, because too great or too small amount of air is detrimental to the user.

Patent publication FI-874 356 discloses a method for regulating the amount of air supplied to a gas mask. In this method, the motor of the blowing unit serves as a sensor for determining the amount of air supplied. The calibration data of the air amount is substantially linked with the characteristics of the entity formed by the motor and centrifugal blower of the blower unit. If some element or characteristic in this entity is changed, the calibration data of the apparatus will be lost.

Patent publication GB-2 032 284 discloses a method for controlling a blower unit by means of a pressure sensor. Thus in this method, the calibration data of the blower unit is dependent on the functioning and condition of the pressure sensor.

Patent publication FI-940 894 discloses a method for regulating the amount of air supplied to a gas mask. In this method, the blower motor and a separate revolution counter are used as sensors. Calibration of the amount of air in the blower unit, as taught in this publication, is based on the utilization of known orifice plates and on apparatus-specific revolution data corresponding to these calibrating plates. Therefore, in this case, the calibration data are not included in the entity formed by the motor and centrifugal blower, like in the arrangement according to FI-874 356, but the calibration data are substantially attached to the calibrating plates and the characteristics of the centrifugal blower. However, the calibrating plates, too, are parts that will wear out and may become damaged.

An object of the invention is to calibrate a blower unit in such a manner that the amount of air supplied by the blower unit to a respirator stays constant even when conditions or component characteristics change. This object is achieved by integrating the calibration so that it becomes an internal feature in an apparatus.

The invention is characterized in that what is specified in the independent claims. Preferred embodiments of the invention are specified in the dependent claims.

The invention is based on the idea that the calibration information is an internal characteristic of the blower unit. Moreover, according to a preferred embodiment of the invention the calibration is controlled by the blower unit, and no auxiliary devices are needed for accomplishing it. So, the calibration information does not depend on the mechanical parts, such as on the properties of the blower unit motor, the centrifugal blower or a flow meter connected thereto, nor on the type of the filters or face piece or dirtiness of the filters. Furthermore, calibration according to the invention can be performed by the user, and a special maintenance person is not necessarily needed.

According to the invention, calibration can be done e.g. utilizing the motor and blower of the device as a sensor measuring the air quantity or using separate flow rate or pressure sensors. Calibration is done using a flow meter and filters or plates in the blower unit. The user always starts the calibration process which also may go on controlled by the user. Alternatively, the calibration process started by a user command can be automated and performed e.g. by means of a computer attached to the equipment. In an embodiment of the invention the blower unit controls the progress of the calibration and saves the calibration data in the blower unit without any auxiliary devices. All that is needed to perform the calibration are the abovementioned flow meter and filters or plates.

In a preferred embodiment of the invention the calibration of a blower unit is per- formed such that a real filter or an orifice plate is attached to the blower unit. Also several different filters or plates, which represent filters used in actual operation, can be used successively in the calibration. It is typical of an arrangement according to the invention that the filters or plates need not be precisely known by their characteristics.

According to a preferred embodiment of the invention, the blower unit or a possible maintenance lid therein need not be opened but the calibration can be done by means of an operating push button or buttons or switches or some auxiliary device. By auxiliary device it is meant a computer connected to the blower unit or some other apparatus controlling the calibration. Although no auxiliary device as such is needed in the calibration, such a device may be used to automate and speed up service operations in which calibration is performed identically on a plurality of equipment, for example.

The method and apparatus according to the invention are advantageously used in conjunction with the manufacture of blower equipment. In addition, the method and apparatus according to the invention are useful for the end user e.g. when performing maintenance operations.

The invention is in following described with the accompanying drawings where

Fig. 1 shows an apparatus according to a preferred embodiment of the inven- tion, and

Fig. 2 illustrates as a flow diagram the calibration of an apparatus according to a preferred embodiment of the invention.

Fig. 1 shows a blower unit 100 to be calibrated. The blower unit 100 of Fig. 1 includes an operating switch 101, indicator means 102 and two filters 103. A flow meter 106 is additionally connected with the blower unit 100. It can be connected to the blower unit 100 direct or, as in Fig. 1, there may be a tube 105 between the flow meter 106 and blower unit 100. The tube 105 allows the flow meter 106 to be placed farther away from the blower unit 100 which may make it easier to read the meter. If necessary, an automating auxiliary 107, such as a computer, for example, may be connected to the blower unit 100. In addition to the elements shown in Fig. 1, a blower unit typically includes a motor, centrifugal blower, batteries and control electronics. Moreover, a blower unit may include a display and one or more flow rate or pressure sensors.

Air flow must be observed in order to control the amount of air in the blower unit 100. To determine the air flow it is possible to use the motor and blower unit as a sensor, or special flow rate or pressure sensors. The flow meter 106 may be a blade wheel anemometer, hot-wire anemometer, a meter based on pressure difference and orifice plate, rotameter or some other known device for measuring flow.

The blower unit 100 to be calibrated is started with the operating push button 101 or similar switch which could be e.g. the main power switch of the unit. The blower unit 100 may indicate the starting of operation through the indicator means 102, for example. The indication may be e.g. a light or sound indication or a combination thereof, indicating to the user a certain function or mode of the apparatus or prompting the user to carry out a certain operation.

The flow diagram of Fig. 2 depicts the calibration of a blower unit according to a preferred embodiment of the invention. Initially, at step 201, the blower unit is started by pressing an operating push button and the blower unit indicates a successful start by giving a short audible or visual signal, for instance. If the operating switch is released in a certain time, say five seconds from the start signal, the blower unit enters normal operating mode in step 202. In the normal operating mode of block 202 the apparatus can be switched off 204 by pressing a certain push button, when necessary.

If the blower unit is to be calibrated for a certain flow, the operating push button is not released after the start signal, but it is waited that the unit gives a new signal in step 203, after which the operating push button is released and operation progresses into step 205. If the operating push button is not released after the second signal given at step 203, the apparatus is switched off 204 almost immediately, say in one second. When the operating push button is released after the second signal, the blower unit enters block 205 to wait for the user to set the blower in calibration mode.

In the wait state of block 205, the blower unit preferably issues a repeating sound or light signal at 1 to 2 Hz. Enter calibration mode' command is advantageously a so- called switching sequence carried out in step 206 using the operating push button or switch, which sequence consists of activation periods of different lengths of the operating push button and pauses of certain duration between those periods. Presses or activations and pauses can be synchronized according to sound or light signals issued by the blower unit. A switching sequence performed with an operating push button for entering the calibration mode of block 207 could be e.g. as follows: a press of 3 seconds, pause of 2 seconds, press of 2 seconds, pause of 3 seconds and a press of 1 second. If the user enters the switching sequence successfully, the blower unit enters the calibration mode of block 207. If the user failed to give the correct switching sequence, the blower unit is switched off at step 204. In the switching sequence of block 206 it is to be noted that the durations of the pauses and activation periods include a tolerance which enables the user to enter the switching sequence. On the other hand, the switching sequence has to be so complex that it is not likely to be entered by chance. Having entered the calibration mode 207 the blower unit again indicates changes in its state using sound or light signals in step 208. This also tells the user to insert in the blower unit a new filter or a corresponding orifice plate for calibration. A flow meter is also connected to the blower unit either direct or through some medium such as a tube, for example. Having installed the filter or orifice plate and the flow meter the user signals this by pressing an operating push button, for instance. The blower unit then enters step 209 and starts slowly increasing the flow rate. As the flow rate increases, it is monitored by means of the flow meter. The flow rate is increased until it is signaled that the desired flow rate has been reached. When the sufficient flow rate has been acknowledged, at step 209, the blower unit will remain operating at the rate in question. At the same time the blower unit saves the necessary information, at step 210, for calibrating the adjustment of the air amount. This information can be saved e.g. in electrically erasable programmable read only memory (EEPROM), random access memory (RAM) with battery back- up, in Flash-RAM, or in non- volatile RAM (NVRAM). Information saved at step 210 may include e.g. the revolution rate, motor current and voltage, or information obtained from a flow rate or pressure sensor integrated in the blower.

After the calibration information has been saved at block 210, the blower unit, in accordance with a preferred embodiment, re-enters the block 208 and issues a sound or light signal. After that the blower unit waits for the insertion of another, say blocked, filter or a corresponding orifice plate in the blower. When this has been acknowledged, the blower unit continues with the calibration as described above at step 209. The calibration may include one or more rounds of steps 208-210, performed with different filters or orifice plates. When the calibration is complete, the blower unit has at its disposal the parameters measured and saved during the calibration process. Finally, at step 211, the blower unit indicates with a sound or light signal that the calibration process is complete, and the unit is switched off at step 204.

The user may verify that the calibration was successful by starting the blower in the normal manner and checking that the blower keeps the air amount constant at the set value with all applicable filters. The calibration, as described above, can be done without any special auxiliary devices and without opening the blower unit. A special maintenance person is not needed, either, as the user can carry out the calibration because the equipment will monitor and guide the calibration process, and no additional devices are necessary. The calibration command by which the blower enters to a calibration mode, i.e. the switching sequence to enter, may be like the one described in previous or alternatively e.g. such that the blower unit gives audible or visible signals at a certain beat, and the user enters the switching sequence with short presses of an operating push button at certain audible or visible signals. A switching sequence may be realized e.g. in such a manner that the user presses the push button only at the fifth, seventh and tenth audible or visible signal. Pressing the push button at other signals will result in a rejected switching sequence. There are countless different possibilities to realize the switching sequence using an operating push button.

In addition to entering calibration mode through a switching sequence entered with an operating push button, the switching sequence may also be realized using a plurality of operating push buttons. This way, the switching sequence may be a combination produced by pressing different push buttons sequentially, or a combi- nation produced by pressing different push buttons simultaneously. Furthermore, the command may be a time-critical switching sequence combined with a switching sequence produced with different push buttons or a combination of push buttons.

Within the scope of the invention it is furthermore possible that the switching sequence for entering the calibration mode is given by means of a computer or a special purpose-built device which gives an appropriate switching sequence to the blower unit. A computer or some other auxiliary can be electrically connected with the blower through a connector, or the switching sequence can be sent via an infrared link, a radio link, as an acoustic signal, or via a magnetic or capacitive data transmission channel.

Claims

1. A method for calibrating the air flow rate on a respirator blower unit, characterized in that it comprises steps of:

- setting the blower unit is set in a special calibration mode (207),

- issuing a prompt for attaching a certain first constant load to the blower unit (208),

- in response to a certain signal indicating the attachment of a first constant load, starting to change (209) the rate of the air flow produced by the blower unit,

- in response to a certain first signal indicating reaching of the desired air flow rate, stopping the changing of rate of the air flow produced by the blower unit and saving certain control information (210) describing the operation of the blower unit at that air flow rate at which the changing of the air flow rate was stopped, and

- using the saved control information for producing such general control information which describes the operation of the blower unit producing an air flow at a constant rate.

2. A method according to claim 1, characterized in that after saving the control information (210), issuing a new prompt for attaching a certain second constant load to the respirator (208) and producing certain second control information (209), which is also used to produce such general control information which describes the operation of the blower unit producing an air flow at a constant rate.

3. A method according to claim 1, characterized in that setting the blower unit in the calibration mode in response to a switching sequence (206) entered by means of an operating push button on the blower unit, which switching sequence comprises several on and off periods of the operating push button.

4. A method according to claim 3, characterized in that it comprises steps of in response to applying the operating push button, issuing a first signal, and in response to keeping the operating push button applied for a certain period of time after the issuing of the first signal, issuing a second signal, whereby the setting of the blower unit in the calibration mode is canceled (204), if the operating push button is not kept applied till the issuing of the second signal or if the operating push button is kept applied for a period of time after the issuing of the second signal, which period of time is longer than a certain maximum period of time.

5. A method according to any of claims 3 to 4, characterized in that the switching sequence (206) comprises such on and off periods of the operating push button which have to be accomplished in certain relation to individual signals of a certain signal sequence sent during the switching sequence (206) for the switching sequence (206) to be accepted.

6. A method according to claim 1, characterized in that setting the blower unit in the calibration mode (207) in response to a control command given by means of a special control device.

7. A method according to claim 1, characterized in that the signals (208) indi- eating the attachment of a constant load, and the signals (209) indicating that the desired air flow rate has been reached, are signals given by means of an operating push button on the blower unit.

8. A blower unit of a respirator, characterized in that it comprises

- means (101) for receiving a command concerning the setting of the blower unit in a special calibration mode,

- means (102) for issuing prompts concerning the attachment of constant loads to the blower unit,

- means for controllably changing the rate of the air flow produced by the blower unit in response to certain signals,

- means for stopping the changing of the rate of the air flow produced by the blower unit in response to certain signals,

- means for saving control information which describes the operation of the blower unit at that air flow rate at which the changing of the air flow rate was stopped, and

- means for producing on the basis of the control information saved, such general control information which describes the operation of the blower unit when it produces an air flow at a constant rate.

9. A blower unit according to claim 8, characterized in that the means for receiving a command concerning the setting of the blower unit in a special calibration mode comprises an operating push button (101) for the blower unit.

10. A blower unit according to claim 8 or 9, characterized in that the means for issuing prompts (102) comprises audio signaling means.

11. A blower unit according to any of claims 8 to 10, characterized in that the means for issuing prompts (102) comprises light-based signaling means.