an example of a problem solved by the present invention is provided by the applicant &# 39 ; s autoset ® t device , which is provided with a “ loop back ” box which facilitates the optional connection of a humidifier into the air delivery circuit upstream of the pressure transducer . the arrangement is described in co - pending australian patent application no . 71978 / 98 filed 18 jun . 1998 and is schematically illustrated in fig1 ( a ) to ( d ) hereof . fig1 ( a ) and ( b ) show the correct manner in which the loop back box and the humidifier are intended to be connected . in fig1 ( a ) the humidifier is not used , and the loop back box connects the flow generator ( f ) to the internal conduit where the pressure sensor ( t ) is located . the mask ( m ) is connected to its outlet downstream of the pressure sensor . typically the ventilatory assistance for cpap or nippv treatment is delivered to the patient by way of nasal mask . alternatively , a mouth mask , a full face mask or nasal prongs can be used . in this specification , any reference to a mask is to be understood as incorporating a reference to a nasal mask , mouth mask , full face mask or nasal prongs . in fig1 ( b ) the humidifier ( h ) replaces the loop back box and gas correctly flows from the flow generator , through the humidifier , past the pressure transducer and thus to the mask . in order that the autoset ® device be compatible with a large range of standard tubing , humidifiers and masks , the outlets all have the same size and shape . it is therefore possible to assemble the equipment incorrectly , as shown in fig1 ( c ) and ( d ). in fig1 ( c ) neither the loop back box nor the humidifier is used , and the mask is attached directly to the outlet of the flow generator , thus by - passing the pressure sensor . in fig1 ( d ) the mask receives no pressurised air . in either of these situations the pressure transducer will give an incorrect indication of mask pressure and this may lead to a dangerous overpressure in an automatically adjusting device . by monitoring the pressure transducer output in conjunction with motor speed this dangerous condition can be detected and responded to . boundary conditions of high motor speed and low pressure , and low motor speed and high pressure , may be chosen as indicators of a fault condition . the same conditions can also be used to assert a fault in the case of a defective pressure transducer , and are described later in relation to fig6 and 7 . a similar approach enables a stalled motor condition to be catered for in the nippv device without the use of devices such as fuses . a stalled motor will not generate any pressure , and the feedback control loop to the servo unit will cause an increase in motor current . conventionally , a fuse or other cut - out device will be required to protect the motor from overheating . if however , the motor parameters of motor speed and a motor drive parameter such as a function derived from current are monitored , a fault condition may be established . for example , if the motor parameter is greater than 80 % and the motor speed remains below 4 , 500 rpm for 0 . 2 seconds , a “ stalled motor ” condition exists . a “ restricted motor ” condition can also be defined , for example where the motor parameter exceeds 95 % and the motor speed is lower than 15 , 000 rpm , for at least 30 seconds . the corrective action in these cases is to disable the motor and otherwise disable operation of the machine until service can be performed , this mode being termed the “ service required ” mode . malfunction of the motor speed transducer will impact on the detection of motor stall , and on other fault detection functions which will be described below . in this specification there is therefore also described the manner in which the invention may be applied to the detection of motor speed transducer failure . it will be seen that the invention can be put into effect with appropriate software , using the control electronics already provided in the machine , and therefore represents an economical solution to the diagnostic objectives . the invention has a number of advantages over the prior art . firstly , safety can be improved . the greatest proportion of cpap treatment apparatus are for use in a non - clinical setting , in which environment a user is untrained to detect conditions indicative of faults . such fault conditions can lead to the cpap treatment apparatus being ineffective or even dangerous . for example , the flow generators used in certain modern cpap treatment apparatus are capable of delivering pressures in excess of 30 cm h 2 o , which may be required in certain situations , but excessive and potentially dangerous in others . the costs , both direct and associated , of cpap treatment apparatus which include the invention can be reduced . certain hardware such as fuses and other analogue circuitry may no longer be required . furthermore , it becomes cheaper for technicians to diagnose faults since the device may be interrogated by interfacing with the controller , reducing the need to remove casing during service . interfacing may be done locally or remotely , for example through a network . in a clinical setting , this may have the further advantage of reducing patient disturbance . in the cpap treatment device with fault diagnosis , useability is improved . it becomes possible to provide fault diagnosis and rectification information to those without clinical or technical skills . the invention may also be used to predict more accurately when faults may occur , for example , to predict when a flow generator air inlet filter may need changing , based on measurements of the motor load . in the specification , any reference to “ operating parameters ” is to be understood to relate to any form of data or state signal , transducer or actuator , and the mechanical and electrical functions of component elements / apparatus of a cpap apparatus . any reference to “ process ” is to be understood to mean a unit of hardware and / or software which can perform a task or set of related tasks , for example , a fault detection process , a feedback control process , a pressure measurement process or a flow measurement process . following the diagnosis of a current or potential fault occurring , the response may be one or more of the following : issuing a warning of the fault condition , recording a diary entry describing the fault condition , adjusting operating parameters and switching between the functional and stand - by or stop modes , or switching the device to a service - required mode . the response may be immediate , or at some later period , for example , the morning following the sleep period during which the device was used . fig2 shows a simplified schematic of a typical cpap treatment apparatus . an impeller ( 1 ) is powered by an electric motor ( 2 ) using a servo ( 3 ) under the direction of a microprocessor - based controller ( 4 ). the supply of breathable gas is carried to the mask ( 5 ) through a flexible conduit ( 6 ). the apparatus has various switches ( 7 ), displays ( 8 ) and a number of transducers . the transducers monitor a number of processes , for example : volumetric flow rate ( 10 ) ( at a predetermined point in the flow path ), pressure ( 11 ) ( at a predetermined point downstream of the flow generator outlet or at the mask ), snore ( 12 ), flow generator rotational speed ( 13 ) and motor parameter ( 14 ). there may be a relationship between the measured blower flow rate , f , and the measured blower output pressure , p , such that f decreases when p increases . it may be desired that for acceptable operation of the device , the parameter values be kept in a certain region . the function r for that process may be written : distinct functions may be determined for different conditions , for example , high and low motor speeds , as shown in fig3 a and 3 b . alternately , the acceptable region could be defined by a 3 - parameter model , r = r ( f , p , ω ), where ω is motor speed . in a simple case , the acceptable region may be a rectangle , defined by two values of flow f 1 and f 2 and two values of pressure , p 1 and p 2 . if the estimates of the parameter values were { f , p } then the test to diagnose a current fault may be , for example : if p & gt ; p 1 and p & lt ; p 2 and f & gt ; f 1 and f & lt ; f 2 then the current operation region lies within the acceptable range . alternatively , the method may diagnose a fault if { f , p } lay outside the acceptable range for an instant , or lay outside the desirable range for some duration . advantageously , the invention is implemented in software . in this case , no additional hardware is needed . the fault detection software processes may be executed in conjunction with existing software . this is shown in fig4 . the inputs to the controller ( 4 ) are analogue electronic signals indicative of the value of various sensors , transducers and other electronic circuitry . these are converted to digital signals . the hardware parameter values ( 41 ) are passed to one or both of the normal computer software processes ( 44 ) ( for example , feedback control processes ) and the fault diagnosis processes ( 43 ). further parameters may be generated ( 42 ) ( for example , flags ) indicative of the operation of each of the software processes , and passed back into one or both of the software processes . in addition , the processes may generate hardware instructions ( 45 ) ( for example , information to be displayed , or directions to shut down the operation of the cpap device ) which are converted to analogue electronic signals and passed to the relevant hardware . fault diagnosis of each apparatus process may be executed as a distinct software process , or several apparatus processes may be monitored within a single software process . in the preferred mode of carrying out the invention , in each device , a plurality of processes are monitored . these include : modes of fault diagnosis for these processes are described in the following sections . the invention may be used to detect whether the pressure transducers are correctly operating . a consequence of a failure of a pressure transducer ( 11 ) could be overpressure or under - pressure to the mask and thus the patient . to detect such a failure condition , the transducer pressure is monitored ( 11 ) together with motor speed ( 13 ). the regions of faulty device operation are shown in fig5 . logical flowcharts indicating the decision process are shown in fig6 and 7 . if the sensed pressure remains below 2 . 0 cm h 2 o ( 62 ) while the motor speed is above 12 , 000 rpm ( 61 ) for at least 0 . 3 seconds ( 65 ), a fault condition is signalled as a “ pressure transducer low ” failure ( 66 ). if neither condition is satisfied , a timer is reset ( 64 ). in a similar way , if the pressure value remains above 15 cm h 2 o ( 72 ) while the motor speed is below 4 , 500 rpm ( 71 ) for at least 0 . 3 seconds ( 75 ), that corresponds to a “ pressure transducer high ” failure ( 76 ). on detection of either form of pressure transducer failure , corrective action is taken to disable power to the motor ( 2 ) and a notification is given on a display . the user may then check all components in the air delivery circuit for an obstruction or an incorrect connection . an additional embodiment is used for the pressure transducer fault diagnosis mode in conjunction with motor speed . the output from the pressure transducer is split into two signals . one signal , p high remains unfiltered , whilst the other signal is low - pass filtered to become p low . each signal is tested to yield an output of “ pressure transducer high ”, “ pressure transducer low ” or “ ok ”. the conditions for “ high ” and “ low ” are as described above . a signal which is neither high nor low is deemed to be ok . unless the test result for both signals is “ ok ”, a fault condition will be signalled . if the test result for both signals is “ low ”, the fault condition is taken as an indication that the hoses are not connected . a failure of the flow transducer ( 10 ) can cause errors in flow measurement , mask pressure measurement and signal processing ( such as inspiratory flow flattening index , as taught in u . s . pat . no . 5 , 704 , 345 ). this in turn may result in errors in the delivery pressure from the flow generator ( 1 ), compromising the efficacy of treatment . logical flowcharts indicating the decision process are shown in fig8 and 9 . to detect such a fault , the flow transducer ( 10 ) signal is monitored together with motor speed ( 13 ). if the flow remains below 5 % scale deflection ( f . s . d .) ( 82 ) while the motor speed is less than 4 , 800 rpm ( 81 ) for more than five seconds ( 85 ), the fault condition is signalled as “ flow transducer low ” failure ( 86 ). if neither condition is satisfied the counter is reset ( 84 ). in a similar manner , if the flow generator flow remains above 95 % f . s . d . ( 92 ) with the motor speed less than 4 , 800 rpm ( 91 ) for more than 5 . 0 seconds ( 95 ), the fault of “ flow transducer high ” is signalled ( 96 ). on occurrence of either fault condition , the patient is notified on a display , and in addition , the mask pressure will be increased over some time , for example , five minutes , to a predetermined level , in this case , the 95 % centile of the previous session . however if that pressure value would be invalid by representing a dangerous overpressure , the pressure will be limited to 10 cm h 2 o . a failure of the snore index transducer can cause errors in the snore measurement and the calculated snore index . such errors result in consequential errors in the treatment pressure delivered by the flow generator ( 1 ), again possibly compromising the efficacy of treatment . logical flowcharts indicating the decision process are shown in fig1 and 11 . to detect a failed snore transducer the snore transducer signal ( 12 ) and motor speed ( 13 ) are sampled . if the snore index signal remains below 5 % f . s . d . ( 102 ) with the motor speed greater than 11 , 000 rpm ( 101 ) for more than two seconds ( 105 ), a “ snore transducer low ” failure is signalled ( 106 ). if neither condition is satisfied the counter is reset ( 104 ). if the snore transducer ( 12 ) signal remains above 95 % f . s . d . ( 112 ) while the motor speed is less than 6 , 000 rpm ( 111 ) for more than two seconds ( 115 ) a “ snore transducer high ” failure mode occurs ( 116 ). the corrective action that can be taken is to notify the user of the occurrence and , if the flow generator ( 1 ) is generating a pressure , attempt to increase the pressure over some time , for example 5 minutes , to a predetermined level , for example , the 95 % centile of the previous session . if that pressure value is invalid by representing a dangerous overpressure , the pressure will be limited to 10 cm h 2 o . an incorrect motor speed may impact upon functions arising from the pressure transducer ( 11 ), flow transducer ( 10 ) and snore transducer ( 12 ). logical flowcharts indicating the decision process are shown in fig1 and 13 . detection of a failure of the motor speed transducer ( 13 ) is achieved by monitoring the speed ( 13 ) together with the sensed pressure ( 11 ) and flow ( 10 ) and the motor drive parameter ( 14 ). if the motor speed remains below 6 , 000 rpm ( 121 ) while the motor drive parameter is above 15 % ( 122 ) and either the pressure is above 8 . 0 cm h 2 o ( 123 ) or ( 125 ) the flow is greater than 75 % f . s . d . ( 124 ), this set of conditions being true for more than one second ( 128 ), then a “ motor speed low ” failure is signalled as occurring ( 129 ). if any of the conditions are not met , the counter is reset ( 127 ). if the motor speed remains above 18 , 000 rpm ( 131 ) while the motor drive is below 5 % ( 132 ) and ( 136 ) either the pressure is below 2 . 0 cm h 2 o ( 133 ) or ( 135 ) the absolute flow is less than 10 l / min ( 134 ) for more than one second ( 138 ), a “ motor speed high ” failure is signalled as occurring ( 139 ). the corrective action that can be taken is to notify the user of the occurrence and , if the flow generator ( 1 ) is generating a pressure , attempt to increase the pressure over some time , for example 5 minutes , to a predetermined level , for example , the 95 % centile of the previous session . if that pressure value is invalid by representing a dangerous overpressure , the pressure will be limited to 10 cm h 2 o . as noted earlier , a stalled motor will not generate any pressure . such a condition can occur if the impeller ( 1 ) is jammed , for example . the feedback control loop from the flow generator ( 1 ) to the servo unit ( 3 ) will cause an increase in the power delivered to the motor ( 2 ), the increase continuing until maximum power is supplied . a consequence can be overheating of the motor to the extent that insulation or windings fail and the motor must be replaced . flowcharts describing the operation for “ stalled ” and “ restricted ” motor are shown in fig1 and 15 respectively . a motor failure condition is detected by monitoring the motor speed ( 13 ) and motor drive parameter . if the motor parameter is greater than 80 % ( 142 ) and ( 143 ) the motor speed remains below 4 , 500 rpm ( 141 ) for 0 . 2 seconds ( 145 ), a “ stalled motor ” condition exists ( 146 ). if any of the conditions are not met , the timer is reset ( 144 ). in a similar way , if the motor parameter exceeds 95 % ( 152 ) and the motor speed is lower than 15 , 000 rpm ( 151 ), occurring for more than 30 seconds ( 155 ), then a “ restricted motor ” condition exists ( 156 ). the corrective action is to disable power to the motor and otherwise disable operation of the machine until a service can be performed , this mode being termed the “ service - required ” mode . in another embodiment , the method may be used to check the overall pneumatic , or air delivery , performance of the apparatus . the relevant regions are shown in fig3 , being the desired operating region ζ d and fault regions ζ f1 , ζ f2 . the operating regions are a function of pressure ( p ), flow ( f ) and motor speed ( ω ). if , the operational state of the device lies in region ζ f1 , there are several possible causes : if the operational state of the device lies in region ζ f2 , there are several possible causes : the response would be to switch the device to the service required mode . the embodiments described earlier may be used in conjunction with the current embodiment , to distinguish which of the sensors may be faulty . the events “ pressure transducer stuck high ” and “ pressure transducer stuck low ” are mutually exclusive . similarly the flow , snore and motor speed transducers have mutually exclusive conditions . in another embodiment of the invention , the fault diagnosis processes tests whether mutually exclusive conditions have been deduced and signals an error in fault diagnosis if that event occurs . fig1 shows the operating regions for the breath and apnea detection processes . these processes detect the presence of breathing by the user and the occurrence of apneas , these two events being mutually exclusive . during normal operation of the cpap device , either one or the other of these events ought to be detected . in this case , these two events lie within non - intersecting regions of ζ d ( fig1 ). if the current operating region of the device lies outside both these two regions , then some kind of error has occurred and an error is asserted . a flowchart for this fault detection process is shown in fig1 . while the device is operating the “ breath detection ” and “ apnea detection ” processes are monitored . the fault detection process will assert a fault when either of the following two conditions occur : apnea and breath are asserted simultaneously neither apnea nor breath are asserted for a predetermined period . while particular embodiments of this invention have been described , it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof . the present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive , the scope of the invention being indicated by the appended claims rather than the foregoing description , and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein .
a ventilation device for non - invasive positive pressure ventilation or continuous positive airway pressure treatment of a patient has a gas flow generator , a gas delivery circuit optionally including a humidifier , a controller and sensors monitoring values of operational parameters of the device . the device further includes one or more relationships stored in data storage of the controller relating combinations of parameter values as being indicative of fault conditions of the device operation , the sensors and / or the fault detection process .