Measuring and testing – Gas analysis – Solid content of gas
Reexamination Certificate
2001-08-07
2004-08-24
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Solid content of gas
C073S028040, C073S028050, C015S339000
Reexamination Certificate
active
06779380
ABSTRACT:
The invention relates to a measuring system for the monitoring of residual dust for safety vacuum cleaners.
Similar measuring arrangements for the monitoring of the dust concentration in the exhaust air in vacuum cleaners are already known and these employ physical measuring principles such as, for example, the measurement of the differential pressure or of the radiation reflection.
In differential pressure measurement the cc prevailing pressure before the filter unit is compared with the prevailing pressure after the filter unit or after the motor, the differential pressure not being allowed to pass below a threshold value. With a non-defective and unfouled filter the admissible differential pressure is least, the differential pressure increases with increasing blockage of the filter. If the filter cracks, then an inadmissible pressure balance between the chambers before and after the filter arises and the differential pressure falls below the admissible threshold value in the direction of zero differential pressure. The undershooting of the differential pressure with a cracked filter, but also the exceeding of the differential pressure with a blocked filter, can be used as alarm means for purposes of the motor control.
A disadvantage in the measuring principle with the differential pressure method is that the pressure fluctuations, caused by running fluctuations of the motor because of changing volumes and speeds of the suction medium and by differing blocking and quality of the filter, are nevertheless so high that an exact registration of the undershooting or exceeding of the threshold value can be achieved only inadequately especially in the case of low differential pressures.
DE-GM 92 09 407.4 discloses a detection device of filter breakage in vacuum cleaner arrangements, which device uses the principle of infrared radiation reflection for the particle measurement in the exhaust air. In the exhaust air channel of a vacuum cleaner arrangement there are arranged an infrared sender and an appertaining infrared receiver angularly offset to one another on the circumference of the exhaust air channel, long-wave energy being radiated into the exhaust air channel by the infrared sender. This infrared radiation is then partly reflected on the dirt particles flowing through in such manner that the reflection radiation is registered over the infrared receiver offset, for example, by 90° to the infrared sender.
The energy supplying and the measuring signal preparation occurs in an evaluating electronic system connected with the sender and receiver. The measuring field is defined by the overlapping of the respective input and output jet cone.
On concentration rise of the dust particles in the exhaust air channel the IR energy irradiated by the sender is reflected (amplified) on the particles and measured in the receiver and in this manner a threshold value preset in the evaluating electronic system can be overstepped, which threshold value triggers an alarm and/or brings the motor to a standstill. In this manner, a filter breakage is measured and displayed, in order to avoid health-threatening particle emissions into the environmental air, by manual or automatic switching off of the suction motor, and to make possible a filter change in proper time.
A disadvantage in the measuring principle with infrared radiation reflection for the residual dust particle measurement is that the optical system can be very easily soiled, both that of the IR sender and also that of the IR receiver, whereby the measurement signal is falsified, since the dust particles on sender and receiver likewise absorb and reflect IR energy; these dirt particles, however, are not to be measured, since, after all, they do not reflect the actual flow state in the exhaust air channel. This falsification of the measurement signal by fouling can be poorly compensated, since the degree of fouling is constant neither in time nor locally, and therewith cannot be exactly defined. Thereby for an effective measurement, whether technical and/or computational, compensation is possible only very defectively.
A further disadvantage of the measuring principle with infrared radiation reflection for residual dust particle measurement is that measurement is restricted to the focusing range of the sender/receiver, i.e., the measurement field defined by the overlapping of the radiation cones of sender and receiver does not cover the entire cross-section of the outlet tube, whereby outside of the measuring field no particle measurement takes place, which likewise leads to an undefined, poorly compensatable falsification of the measurement signal.
The purpose for this invention, therefore, is to provide a measuring system for residual dust monitoring in safety vacuum cleaners in such manner that the above-mentioned disadvantages of the state of the art are reduced or even eliminated. Specifically, it is found that the measuring system is more sturdy resulting in a more dependable construction. It is also found that the system provides more accurate measurements in the case of low particle concentration in the exhaust air.
Here the measuring system, on the one hand, is to be less subject to fouling and therewith to make possible longer maintenance intervals; on the other hand, it is also meant to make possible a more accurate measurement of the particle concentration in the exhaust air, in order to give more exact information about the state of the filter, as to whether a defect is present or not. It is also to make it possible to determine low dust concentrations in the exhaust air.
For the solution of the problem posed there serves the technical teaching of the present invention.
An essential feature is that, according to the invention, the measuring system of the residual dust monitoring in safety vacuum cleaners provides for at least one measuring electrode mounted upstream behind the filter unit. The measuring element transmits a current signal to a measurement value processing unit. The current signal is produced by contact tension between measuring electrode and particles and depends on the particle concentration.
There arises here a contact voltage through intensive contact of the dust particles carried along in the carrier medium (air) with the material of the measuring electrode. If the dust particles consist of a material which is materially different from the material of the measuring electrode, then there occurs a passing-over of electrons which flow off to the lower potential as a function of the contacting particles and therewith of the particle concentration in the exhaust air. This holds for both electrically conducting particles and electrically insulating particles. With electrically conducting particles the cause of the charge separation lies in the differing emergence work in comparison to the measuring electrode, and with electrically insulating particles the charge separation lies in the different electron affinity in comparison to the measuring electrodes.
In a preferred form of execution of the measuring system for residual dust monitoring for safety vacuum cleaners according to the invention, it is provided that at least one measuring electrode is arranged downstream within the outlet tube behind the filter and behind the turbine, preferably in the end zone of the outlet tube. Also, it must be possible to arrange the measuring electrode in the vicinity of the turbine in the outlet tube or in the motor block of the turbine itself.
In a further form of execution of the inventive measuring system of the residual dust monitoring in safety vacuum cleaners it is provided that at least one measuring electrode is mounted downstream behind the filter or in front of the turbine, preferably directly on or in the near zone of the filter outlet surface. The measuring electrode can, however, also be arranged in an intermediate tube or an intermediate chamber between filter and turbine or else in the vicinity of the turbine in the motor block.
It is preferred that the measuring electrode cover the entire flow cross-section, but
Baker & Daniels
Rogers David A.
WAP Reinigungssysteme GmbH & Co.
Williams Hezron
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