Abstract:
A sniffing leak detector includes a handpiece, supporting a sniffing tip, the detector further including a gas sensor. To promote longer life and obtaining more accurate results, the leak detector is equipped with an acceleration sensor for recording the movements of the handpiece.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a sniffing leak detector as well as methods for operating leak detectors of this kind. 
   BACKGROUND OF THE INVENTION 
   Leak detectors with sniffing facilities are known (c.f., for example, DE-A 24 41 124 and DE-A 199 11 260). In the instance of sniffing leak detection, a unit under test containing a test gas is scanned with the aid of a sniffing tip. If a leak is present, test gas will escape to the outside. It is then supplied by the sniffing tip to a gas detector or gas sensor. The signals produced by the gas detector serve, among other things, the generation of alarm signals, preferably of the acoustic type. Frequently, helium serves as the test gas. Also a working gas present in any case within the unit under test may be employed as the test gas, in cooling facilities a halogen gas, for example. 
   SUMMARY OF THE INVENTION 
   It is the objective of the present invention to improve several aspects of a leak detector of the kind affected here, as well as the leak detection methods performed with such a leak detector. 
   In the instance of a leak detector of the typical kind, this objective is attained by equipping it with an acceleration sensor. This acceleration sensor may, for example, serve the purpose of letting the leak detector instrument enter the standby mode when not in use and “waking up” it upon use. An other possibility of employing the acceleration sensor is the suppression of interfering signals from a gas sensor being sensitive to movements. 
   While operating, sniffing leak detectors must not necessarily be operated by a keyboard. Therefore, previously, switching over of leak detectors to a standby mode was effected only manually. This type of switchover is inconvenient and is either forgotten by the user or deliberately not performed. By accommodating, in accordance with the present invention, an acceleration sensor in the sniffing facility at the connecting line, for example, or preferably in the handpiece, the instrument itself is capable of detecting whether the user is performing a sniffing leak detection process or if he has deposited the handpiece. With the handpiece deposited, the instrument automatically switches to the desired standby mode. The advantages of this mode—increased service life, energy-saving etc.—can be utilised. 
   It is especially expedient, when during the standby mode not the entire power supply voltage is switched off, but instead only the gas supply pump through which the measurement gas is taken in is switched off when the handpiece is not moved for a longer period of time. In this manner not only the service life of the pump but also that of the detection sensor system which is susceptible to contamination and the filters through which the measurement gas flows, can be increased. Since during the standby mode the sensor system and the electronics are not switched off, the leak detector will be immediately ready for operation as soon as the handpiece is moved once more. 
   In the instance of sniffing leak detectors it is known to accommodate the gas sensor in the handpiece itself, so as to attain short response times. This applies in particular to sniffing leak detectors which consist of the handpiece and a supply unit separated therefrom. The connecting line extending between the handpiece and the supply unit needs to be relatively long (5 m, for example), so that pumping of the measurement gas from the sniffing tip to the supply unit would take up a relatively long time. If the gas sensor is of the type being sensitive to movements (for example, an infrared sensor as it is known from DE-A-199 11 260), the movement of the handpiece causes interfering signals which may result in incorrect measurement results. By employing an acceleration sensor, such interfering signals can be detected and, for example, suppressed. This may be implemented in the simplest case, by interrupting the measurement signal line as soon as signals are produced by the movement sensor. Through these measures the process of sniffing leak detection is rendered more simple and more reliable. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages and details of the present invention shall be explained with reference to the examples of embodiments depicted in drawings  1  to  5 . 
       FIGS. 1 and 2  schematically represent leak detectors of the kind affected herein; and 
       FIGS. 3 to 5  block diagrams for solutions serving the purpose of suppressing interfering signals in the instance of employing gas sensors being sensitive to movements. 
   

   DETAILED DESCRIPTION 
   In the drawing  FIGS. 1 and 2  the leak detector is designated as  1  and the handpiece as  2 . The handpiece  2  carries a sniffing tip  5 . This is equipped with two gas inlet apertures  7  and  8  at different locations. Gas inlet aperture  7  is located in the end section of sniffing tip  5  at the front. It serves the purpose of accepting the measurement gas which in the case of a leak contains the test gas. Through the gas inlet aperture  8 , reference gas from the vicinity of the unit under test, not depicted, is taken in for the purpose of taking into account test gas backgrounds. 
   The solutions according to drawing  FIGS. 1 and 2  differ in that in the instance of the embodiment in accordance with drawing  FIG. 1 , all components of the leak detector  1  are accommodated in the handpiece  2  itself, whereas in the instance of the embodiment in accordance with drawing  FIG. 2 , a handpiece  2  and a therefrom separated supply unit  3  is provided. 
   The gas sensor  11  is located in handpiece  2 . The gas which is to be analysed for the presence of the test gas is sucked in with the aid of a supply pump  15  and supplied to the gas sensor  11  (dashed lines  13 ). In the solution in accordance with drawing  FIG. 1 , the supply pump  15  is located in the handpiece  2 , in the solution in accordance with drawing  FIG. 2  it is accommodated in a separate supply unit  3 . Moreover, the acceleration sensor  16  is located in handpiece  2 . Said acceleration sensor supplies its signals to a supply, measurement and a display circuit  14  depicted by way of a single block, which in the instance of the solution in accordance with drawing  FIG. 1  is accommodated in the handpiece  2 , and which in the instance of the solution in accordance with drawing  FIG. 2  is accommodated in the supply unit  3 . A loudspeaker  17  is depicted as an example for an alarm indicator. It receives its signals from block  14  and may also be accommodated in handpiece  2  (drawing  FIG. 1 ) or in the supply unit  3  (drawing  FIG. 2 ). 
   Also the supply pump  15  is linked in the instance of both embodiments with the block  14 . Via this link the supply pump may be switched off and thus the leak detector switched to the desired standby mode when the handpiece has been deposited, and as long as the acceleration sensor does not supply any signals during a pre-selected period of time. 
   In the solution in accordance with drawing  FIG. 2 , the handpiece  2  and the supply unit  3  are linked by a line  18 . Depending on the distribution of the individual components in the handpiece  2  and in the supply unit  3 , the line  18  comprises electrical and/or gas carrying lines. 
   With reference to the drawing  FIGS. 3 to 5  it shall be explained how with the aid of the acceleration sensor  16  signals suffering interference due to movements of the handpiece  2  can be suppressed. An infrared sensor  20  is depicted schematically as an example for a gas detector which is sensitive to movements. It comprises a cell  21  to which there is assigned on one face side an infrared light source  22 , and on its other face side an infrared light detector  23 . Whilst performing the leak detection process, gas flows through cell  21 . The connections in the area of the two face sides are designated as  28  and  29 . 
   Drawing  FIG. 5  depicts an example for the means of producing the gas flow in the cell  21  (cf. also German patent application 100 62 126.0). With the aid of the gas supply pump  15  which is linked to the connection  29  of the cell  21 , measurement gas and reference gas are taken in through the sniffing tip  5  with its gas inlet apertures  7  and  8 . The schematically depicted unit under test  31  exhibits a leak  32  so that test gas is contained in the measurement gas. A control valve  33  serves the purpose of alternately supplying the measurement gas and the reference gas to the cell  21 . The pump  15  defines the velocity at which these gases flow axially through the cell  21 . An amplifier  34  is connected to the infrared light detector  23 . An indicator (acoustic, optical) is designated as  35 . 
   In the instance of performing sniffing leak detection on a unit under test, locations where a leak is suspected (soldered joints, connections etc.) are scanned one after the other with the sniffing tip  5  of the handpiece  2 . During this scanning phase the handpiece is moved relatively slowly. The signals delivered by the gas sensor are not impaired. The acceleration sensor provides no or only negligibly small signals. The signals delivered by the infrared light detector  23  shall not be suppressed. If a leak is present, the signals reaching the indicator  35  provide, preferably, the acoustic alarm. 
   When moving the sniffing tip  5  from one location suspected of having a leak to a different location or to its rest, the handpiece is commonly moved relatively fast. Alone the interfering signals supplied by the gas sensor which is sensitive to movements can cause an alarm although no leak was determined. Interfering signals of this magnitude shall be suppressed. In this it is expedient to define a limit value and to select this limit value depending on the sensitivity desired for the leak detection process. If, for example, it is demanded that in the instance of units under test all leaks exceeding 3 gram per year shall be indicated, then it will suffice to suppress only such interfering signals which would supply an indication exceeding 3 g/yr. 
   The simplest means of suppressing interfering signals is to switch these off. Drawing  FIG. 3  depicts an example of such an embodiment. A, preferably, electronic switch  36  is located between the amplifier  34  and the indicator  35 . The signals supplied by the acceleration sensor  16  being sensitive in two or three axes are initially supplied to a summing stage  37 . As soon as the signals supplied by the summing stage  37  exceeded a certain value, the path of the measurement signal between detector  23  and indicator  35  is interrupted. The limit value is set up in block  38  which in block  39  between stage  37  and switch  36  defines a threshold. 
   In the solution in accordance with drawing  FIG. 4 , the signals supplied by block  39  influence the amount of gain in the path of the measurement signal. The signals from block  39  are supplied to the amplifier  34  and effect a significant reduction in the gain factor. 
   In the embodiment in accordance with drawing  FIG. 5 , the signals supplied by the acceleration sensor  16  are supplied to a changeover switch  41 . As long as signals of this kind do not reach the changeover switch  41 , the changeover switch  41  assumes the position indicated by the solid line. The measurement signals of the infrared light detector  23  arrive at indicator  35 . If signals from the acceleration sensor  16  caused by movements of the handpiece  2  arrive at the changeover switch  41 , it switches to the position indicated by the dashed line, before measurement signals of detector  23  suffering interference can arrive at the indicator. 
   Through the solution in accordance with drawing  FIG. 5  it shall be achieved, that brief interruptions in the path of the measurement signal are not noted and longer interruptions are initially not noted by the user. The means proposed to this end comprise blocks  42 ,  43  and  44 . Block  42  is located between the changeover switch  41  and the indicator  35 . Said block has the function of a filter and, if required, that of a lock-in logic circuit. It is linked to block  43  which has the task of simulating a measurement signal. After switch  41  has switched over to the position indicated by the dashed line the signals simulated by building block  43  and which correspond to the signals provided by the preceding measurement signals pass via building block  42  to indicator  35 . In the instance of short, hasty movements of the handpiece  2  the measured values are indicated continuously. By employing a lock-in amplifier it is possible to simulate, for example, the not yet demodulated sinusoidal signal whereby the indicated value is taken as a reference. 
   If the acceleration sensor  16  supplies signals over a prolonged period of time, meaning that the switch  41  assumes the position indicated by the dashed line for a longer period of time, then it is expedient to let the simulated signals decay slowly, preferably at such a speed with which also the measurement signal indicator decays upon terminating a leak search. Block  44  being located between block  43  and the changeover switch  41 , has the function of a timer logic suited for this purpose. 
   Circuit blocks having certain functions are depicted in the drawing  FIGS. 1 to 4 . Many parts of the circuit may also be implemented with the aid of a microcomputer with suitable software.