WO2016074832A1

WO2016074832A1 - Particle counter

Info

Publication number: WO2016074832A1
Application number: PCT/EP2015/071416
Authority: WO
Inventors: Frank Fischer; Reiner Schnitzer; Gael Pilard
Original assignee: Robert Bosch Gmbh
Priority date: 2014-11-13
Filing date: 2015-09-18
Publication date: 2016-05-19
Also published as: DE102014223151A1; TW201621295A

Abstract

The invention relates to a particle counter having a laser light source (10) and a photodetector (20). The core of the invention consists is that the particle counter has a laser scanner (30) with at least one deflectable mirror which is deflectable about at least one axis of rotation.

Description

Description title

Particle counter prior art

The invention is based on a particle counter with a laser light source and a photodetector.

Particle counters are devices for detecting the size and number of particles in liquids or gases.

Various devices for particle measurement and particle counting are known in the art.

The basis for the scattered light particle counter is a laser light source, a

Photodetector and a measuring cell through which an air stream is drawn. The method is based on sending a laser beam through the airflow. If it hits a particle, scattering occurs, which is measured by means of a detector.

It is important that the detector has a high sensitivity, because the intensity of the scattered light is low and dependent on the particle size. This requires that it is dark inside the measuring cell. Furthermore, the particles must be conducted by means of the air flow into the measuring cell.

Object of the invention

The object of the invention is to provide a device for particle measurement with low power consumption and small size for mobile use or as a sensor for networked systems. Advantages of the invention

The essence of the invention is that the particle counter a

Has laser scanner with at least one deflectable mirror, which is deflectable about at least one axis of rotation.

Advantageously, the laser light can be guided to the particles, whereby the measuring cell and the device for generating the air flow can be omitted. An advantageous embodiment of the invention provides that the photodetector is a single photon avalanche diode (SPAD) or a SPAD array. Advantageous is the high sensitivity and low response time, which

Stray light measurements can be recorded from a specific area or space segment whose length is determined by the measurement time. An advantageous embodiment of the invention provides that the deflectable mirror is a MEMS micromirror. Advantageously, the device can hereby be made very compact and cheap.

An advantageous embodiment of the invention provides that the deflectable mirror is deflectable by two, in particular orthogonal, axes of rotation.

This can be advantageous particle measurements in a specific

Space segment are made.

An advantageous embodiment of the invention provides that the particle counter comprises an evaluation device which is set up to count particles and / or to measure particles. Advantageously, the number of particles can be determined from the number of intensity changes of the light incident on the photodetector. Advantageously, the size of the particles can be determined from the intensity of the light incident on the photodetector.

An advantageous embodiment of the invention provides that the particle counter a focusing optics for focusing a laser beam from the laser light source has, wherein the focusing optics is adapted to cause a beam diameter in the focus <lmm, in particular <10μηη.

An advantageous embodiment of the invention provides that caused by the focusing optics focal length within a through a measuring time window of the

Photodetector predetermined measuring distance is.

An advantageous embodiment of the invention provides that the laser light source for emitting light with a wavelength <550 nm is set up.

It is advantageous that the laser beam is focused so that the waist of the

Beam within the distance to come, which corresponds to the predetermined by the time interval measurement window. The beam diameter in focus should be <1 mm, preferably <100 μm, particularly preferably <10 μm.

An advantageous embodiment of the invention provides that the laser beam is operated with a power that enables safe operation. The

Laser power is chosen according to the wavelength and pulse shape such that according to the industry standard "IEC 60825-1: 2007, Edition 2 - Safety of laser products - Part 1: Device classification and requirements" a

Classification in Class I or Class II.

Based on the scattered light principle, the following aspects are improved in the present invention in an improved manner:

In the scattered light measurement, a SPAD diode or a SPAD diode array is used, which has a high sensitivity. In this case, a laser (wavelength 350-950 nm, preferably <660 nm, particularly preferably <470 nm, in particular 405 nm) is pulsed and the scattered light is evaluated only within a time window after the respective pulse and compared with the dark counting rate. As a result, only the scattered light of particles is determined, which are located in a time window corresponding distance to the device. A preferred measurement distance is at a distance from the photodetector in the range 0.5-100 cm, preferably 1-25 cm, more preferably 3-10 cm. This corresponds to one

Time window for detection from 180 ps to 600 ps after emission of the light. Reflections of the laser light from objects that also scatter light in the scanned space in front of the device are thereby ignored. Around To reduce background light can be a narrowband filter in front of the

Collection optics are used or measured in a shaded space outside. For a mobile application, the background light level can also be reduced by directing the test laser to a dark object at a distance of less than 100 cm but not closer than the maximum; e.g. at a distance of about 20 cm on the shaded palm of a user at a test track 3-10 cm.

The components already integrated for a projector in a mobile phone or smartphone, such as e.g. The light source, micromirror and S PED detector, for example for the additional application distance measurement, can thus be used for another application to carry out particle measurements and thus to determine the air quality, for example.

In the device according to the invention for the detection of particles, no medium has to be sucked in. The structure can be designed very compact (volume <1 cm ³ ). Production costs of considerably less than 10 US dollars are possible.

drawing

Figure la shows a scattered light particle counter with a laser light source, a

Measuring cell and a photodetector in the prior art.

Figure lb shows a scattered light particle counter according to the invention with a

Laser light source, a 1D or 2D scanner and a SPAD detector.

Figure 2 shows a structure for particle measurement with an inventive

Scattered light particle counter.

FIG. 3 shows a timing diagram for a measurement with a scattered light particle counter according to the invention.

embodiments

Figure la shows a scattered light particle counter with a laser light source, a measuring cell and a photodetector in the prior art. Shown are one Laser light source 10, a photodetector 20 and a measuring cell 40. An air flow 50 is passed through the measuring cell 40. The air flow contains the particles 60 to be counted or measured. The illumination with the laser light source 10 is static. The scattered light measurement is carried out with the photodetector 20.

Figure lb shows a scattered light particle counter according to the invention with a laser light source, a 1D or 2D scanner and a SPAD detector.

Shown is a laser light source 10, a 1D or 2 D scanner 30 and a SPAD detector 20. The 1D or 2D scanner 30 has a mirror oscillating in one or two directions, in particular a MEMS micromirror. During measurement operation, a pulsed laser beam 15 having a wavelength between 1100 nm and 400 nm, preferably <700 nm and a pulse length of 0.1-10 ns, is emitted by the laser light source 10 and directed onto the scanner 30. The laser beam 15 is picked up by the 1D or 2D scanner 30 with the mirror swinging in one or two directions to form a 2-dimensional fan or a 3-dimensional hopper. With this scanning laser beam, the area is illuminated in front of the particle counter according to the invention, and indeed within the spanned viewing angle 70. If particles 60 are within the scan range, a small part of the laser radiation is scattered and directed to the detector 20. The scattered light can pass through a filter 90, which is narrowbanded around the laser wavelength. The detector is preferably a SPAD (Single Photon Avalanche Diode). Advantage of the SPAD is the high sensitivity and short response time. In the case of light measurement in a corresponding short time window, only measurement signals are considered which are within a viewing length 80 of 3-10 cm or up to 0-100 cm. This is achieved in that the scattered light measurement is carried out only in a time interval of 0 - 10000 ps, preferably 180 - 600 ps.

Figure 2 shows a structure for particle measurement with a scattered light particle counter according to the invention. The figure is a schematic sketch along the optical path (cross section of FIG. 1b). According to the invention is a

Laser beam 15 with a very small diameter of 0.001 mm - 1 mm, preferably 1 μηη - 200 μηη, more preferably <10 μηη used. This can

For example, by focusing optics 100 of laser 10 is set so that the beam 15 to a point in the midst of

Measuring section 110 is focused and thus a small diameter over the entire measuring section 110 receives. This ensures that an increased luminance is created and the signal of the reflected light is improved. Also improves the signal-to-noise ratio over the

Ambient light. In FIG. 2, the reflected light component 130 from the scattering by a particle 60 is shown by way of example, which is directed via a collection optics 120 onto the detector 20 (SPAD or SPAD array).

FIG. 3 shows a timing diagram for a measurement with a scattered light particle counter according to the invention. The limitation of the measuring time to the measuring path is according to the invention e.g. realized in that the SPAD diode is activated only within a measuring window 200 active. This happens because the bias voltage of the SPAD is initially kept below the breakdown or Zener voltage and only for the measurement to the operating value (active) is pulled above the Zener voltage. After the measurement window, the voltage is reset to the inactive value. Within the measurement window 200, scattered light and background light are measured. A reference measurement 300 takes place in an identical measurement interval as is selected for the scattered light measurement, but the measurement takes place without a preceding laser pulse. In the reference measurement 300, therefore, only one measurement of the background light takes place. For the limitation of the measuring section 110 to a value clearly <Im, it is important that the length of the laser pulse is also small. The length of the pulse should not exceed the corresponding duration for the measurement path 110 by a factor> 10 (e.g., pulse length 500 ps, measurement window between 180 ps and 600 ps).

The use of other photodetectors known in the art is also possible.

LIST OF REFERENCE NUMBERS

10 laser light source

15 laser beam

20 photodetector

30 scanners

40 measuring cell

50 airflow

60 particles

70 viewing angles

80 viewing length

90 filters

100 focusing optics

110 measuring section

120 collection optics

130 reflected light component

200 measuring windows

300 reference measurement

Claims

claims

1. particle counter with a laser light source (10) and a photodetector (20),

characterized in that

the particle counter has a laser scanner (30) with at least one deflectable mirror which can be deflected about at least one axis of rotation.

2. Particle counter according to claim 1, characterized in that the photodetector (20) is a SPAD or a SPAD array.

3. Particle counter according to claim 1 or 2, characterized in that the deflectable mirror is an M EMS micromirror.

4. Particle counter according to one of the preceding claims, characterized in that the deflectable mirror is deflectable about two, in particular orthogonal, axes of rotation.

5. Particle counter according to one of the preceding claims, characterized in that the particle counter comprises an evaluation device which is adapted to count particles and / or to measure particles.

6. Particle counter according to one of the preceding claims, characterized in that the particle counter has a focusing optics (100) for focusing a laser beam (15) from the laser light source (10), wherein the focusing optics (100) is adapted to a beam diameter in the focus of <1 mm, in particular <10 μηη cause.

7. Particle counter according to claim 6, characterized in that a focal length caused by the focusing optics (100) is within a predetermined by a measuring time window of the photodetector (20) measuring distance.

8. Particle counter according to one of the preceding claims, characterized in that the laser light source (10) for emitting light with a

Wavelength <550 nm is set up.

9. Particle counter according to one of the preceding claims, characterized in that the laser light source (10) is a class I or class II laser.