DE2945608A1 - Flue gas concentration determn. - using extra light chopper and band-pass filter in receiver - Google Patents

Abstract

The concn. of the components of a flue gas mixt. contg. various gases and also smoke particles is determined by measuring the optical radiation which has passed through the mixture and has been reflected back through it to a photoelectric transducer. A light chopper (electro-optical modulator, rotating chopper disc, rotary prism) is arranged between the measuring space and the reflector. The receiver includes at least one selective band- pass filter for the suppression of any d.c. voltage components. This prevents erroneous readings by the light which is back scattered in the measuring space, and restricts the measurement to the light reflected by the reflector.

Description

The invention relates to a device according to the preamble

of claim 1.

In a known device this working in autocollimation Device (DE-AS 25 21 934) can be a backscatter of the reaching into the measuring section Light especially when there is thick smoke in the measuring section to incorrect measurements lead because the backscattered light is interpreted as reflected light, though it has not completely traversed the test section.

The aim of the invention is thus to provide a device of the initially mentioned to create named genus, in which only that reflected by the measuring reflector Light is detected on the receiving side.

To solve this problem, the invention provides that between the measuring section and measuring reflector, a light chopper and a band filter provided on the receiving side is which suppresses DC voltage components. This way both that light scattered back directly from the measuring section as well as other direct, Extraneous and basic light not perceived in the receiver. For the test receiver comes the light apparently only from the reflector incorrect measurements are thus effectively avoided. Although the device according to the invention works in autocollimation, it has the significant advantages of such systems, in which sender and receiver at opposite ends of the measuring section are housed.

Advantageous further developments of the invention are given by the subclaims marked.

The invention is illustrated below, for example, with reference to the drawing described; 1 shows a functional diagram of a preferred device according to the invention and FIGS. 2, 3 intensity-frequency diagrams when used two choppers.

According to the drawing, the device has one on one side a chimney 72 attached light transmitter-receiver 11 and one on the opposite Side of the chimney 72 attached reflector head 12, which consists of a housing 14 and a retroreflector 13 arranged on its end face. To the passage the bundle of light points the chimney 72 in the area of the light transmitter-receiver 11 and of the reflector head 12 openings 74, 75.

The housing 14 of the reflector head 12 and a connecting piece 76, which connects the housing 15 of the light transmitter-receiver 11 to the chimney 72 are provided with purge air supply nozzle 71, through which in the direction of the arrows f Purge air is blown in, which prevents impurities from getting out of the chimney 72 get into the connecting piece 76 or to the front lens 20 and there drop.

One is preferably in the housing 15 of the light transmitter-receiver 11 A radiation source 16 formed by a mercury vapor low-pressure lamp is attached, which via the condenser 19, possibly a chopper 7 and a beam splitter mirror 77 illuminates a front lens 20 arranged in the end wall of the housing 15. An almost parallel and preferably slightly divergent one emerges from the front lens 20 Light bundle 50 from which the connection piece 76, which with smoke gases 49 interspersed Chimney 72 and finally the housing 14 of the reflector head 13 traversed to to hit the retroreflector 13, which preferably consists of triples. Essential is that the light bundle 50 at the location of the reflector 13 is larger in diameter is than the retroreflector 13, so that the reflector 13 is irradiated on all sides is present. In this way, the light flux reflected by the reflector 13 changes not if there are certain shifts or tilts relative to the optical axis occur between reflector head 12 and light transmitter-receiver 11.

Due to the dimensions of the light bundle 50 and of the retroreflector 13, the reflected bundle 78 has a smaller diameter than the also almost parallel bundle 50 emanating from the transmitter.

The reflected beam 78 is through the lens 20 and after reflection Concentrated at the beam splitter mirror 77 on a photoreceiver 17, in front of the a filter wheel 18 is arranged with an axis of rotation 79 parallel to the incident light. The filter wheel 18 is driven to rotate by a motor 80.

A control filter 23 can also be inserted in front of the filter wheel, which corresponds to a predetermined component distribution of the exhaust gases and to Checking the device for functionality is used.

Filters 23, 24, 25 arrive one after the other when the filter wheel 18 is rotated in the beam path running to the photoreceiver 17.

On a further inner circumference of the filter wheel 18 are also over slightly less than 900 each extending in the circumferential direction Arranged slots 34, each of which is assigned to one of the filters. Purpose of Circumferential slots 34 are to generate a clock signal, which electronics in activated appropriately.

Finally is on a third, between the first and second lying circumference still provided a small round control opening 36, which with another light barrier 37 cooperates and for generating a Pückstellungssignal is used for the clock generator and thus for identification of the start of each cycle.

The photoreceiver 17 is preferably a photo multiplier, for complete Drift compensation is between the light transmitter / receiver 11 and the inlet opening 74 in the chimney 72 a comparison reflector 22 is provided, which is exactly the same as the reflector 13 is designed as a triple reflector. The comparison reflector 22 is usually arranged next to the beam path. However, he is in the direction of the Double arrow f in the position shown in dash-dotted lines within the The beam path is displaceable in such a way that the light bundle 50 impinging on it is reflected back in itself.

At any point when switching from measurement to comparison moving part, e.g. on the comparison reflector 22 is a contact piece or a Cam 29 arranged, which cooperates with a contactor 30 in such a way that a clock 28 with inserted comparison reflector 22 a relevant Signal is supplied. In other words, the clock generator 28 can recognize at any time whether the comparison reflector 22, 22 'is effective or not.

The following part describes the electronic structure of the inventive Device described: At the photoreceiver 17 there is a load resistance guided by Nasse 38 arranged at which a voltage fed to a preamplifier 21 is tapped is. The preamplifier 21 contains filter means 8, so it is selective.

The output of the preamplifier has an amplified voltage Uv, which is fed to a channel alignment stage.

The output of the preamplifier 21 becomes seven amplifiers in parallel 41, 42, 43, 44, 45, 46 and 47 supplied with adjustment. This division of the output signal of the voltage amplifier 21 already requires a later channel separation.

The output signals of the amplifiers 41 to 47 with adjustment are made one by one an electronic switch 27 which is controlled by a clock generator 28 which control signals U, from the light barrier 37 and UT from the light barrier 35 receives the filter wheel 18 and also via the contactor 30 the effectiveness or ineffectiveness of the comparison reflector 22 detects.

Each measurement wavelength is for both effective and ineffective Comparison reflector 22 in switch 27 is assigned a holding circuit 51, 52, 53, 54, 55, 56. A seventh hold circuit 57 stores the signal representative of the dark current and leads it through an impedance converter 32 to form a base Input of the channel alignment stage 31 back.

At the output of the switch 27, the holding circuits 51 to 56 are always present six signals are available, of which the signals U'1, U'2 and U'3 are the ones received Signals for the individual measurement wavelengths with the reference reflector inserted 22 correspond, while the signals U1, U2 and U3 for the wavelength signals at effective measuring reflector 13 are representative.

Due to the possibility of adjustment in the amplifiers 41-47, through an adjustment before commissioning the device all output signals the holding circles 51 to 56 are brought to the same level. This is not only true for the individual wavelength signals in comparison to one another, but in particular for when the comparison reflector is switched on on the one hand and the effectiveness of the Measuring reflector on the other hand appearing output signals. That way you can e.g.

also different reflection properties of the measuring reflector 13 and the comparison reflector 22 are easily balanced in the simplest manner will.

The signals U1 to U3 are evaluated in a computing circuit 33.

The three outputs of the computing circuit 33 are then included Display device 69, which e.g. after the voltage current conversion has taken place as a triple recorder with a respective display range of 0 to 20 mA according to specified concentration ranges can be designed so that changes in concentration can be continuously tracked.

The radiation source 16, the drives for the filter wheel and comparison reflector arrangement, the lamps of the light barriers as well as the entire electronics are shared by one Power supply 70 fed.

Between the measuring section 49 and the measuring reflector 13 is according to the invention still a light chopper 10 switched on, which by a control device 9 to it is caused to interrupt the constant light beam 50 periodically. Exists a Need to make the light chopper 10 as small as possible, so he can at the site of a can be attached to a greatly reduced intermediate image. The received light beam 78 therefore consists of periodically chopped light, which is indicated by a dashed representation this bundle is illustrated.

According to the invention, a bandpass filter 8 is thawed into the preamplifier 21, which is tuned to the same frequency f as the control device 9. To this In this way, the receiver arrangement only takes the light reflected from the measuring reflector 13 true, which the measuring section 49 has completely traversed. That, for example Light that is directly backscattered by smoke particles in the measuring section 49 is on the other hand is suppressed by the bandpass filter, between the radiation source 16 and the measuring section 49 also built in the second light chopper 7. so can also the Störz.B. sunlight light / suppressed that falls on the reflector 13 and thus of the invention Light chopper 10 transformed into alternating light and incorrectly interpreted as measuring light would be. The light chopper 8 between the radiation source and the measuring section 49 must have a different chopping frequency than that of the chopper according to the invention 10. There is now a mixture of the two chopper frequencies on the photoreceiver 17 available for evaluation. The filter 8 in the amplifier 21 is therefore allowed to have an output signal Only emit UV when the electrical signal emitted by the phcto-receiver 17 was affected by both choppers.

The filter 8 can take into account that in addition to the two carrier frequencies f7 and f10 two sidebands S1, S2 each arise (FIG. 2). In these sidebands the information from both frequencies is contained at the same time. The filter 8 of the receiver 21 must therefore at least one of the two sidebands S1, S2 one Let the carrier through and block the direct current component. It can use the sideband frequencies f10 + f7 or f7 + f can be evaluated.

A second way to get a signal that has been freed from interfering light is consists in the signal mixture, consisting of a carrier and at least one Sideband, to demodulate and the resulting signal selectively to measure up. After the dodulation it is sufficient to suppress the DC component z. A third possibility is to mix the signal with an auxiliary frequency according to Fig. 3. This results in different mixing frequencies. One of them is chosen which contains the information from f7 and f10. If e.g. according to Fig. 3 f7 with 150 Hz, f10 is selected with 500 Hz and the auxiliary frequency with 450 Hz, among other things the mixing frequency 100 Hz, which is filtered out in the preamplifier 21 by the filter 8 can be and is available as a measuring signal.

The signal is filtered by filter 8 in the example. In principle, however, it is also possible later, e.g.

evaluate with a digital filter. This can be done, for example, in a microprocessor.

The degree of modulation of the chopper does not have to be 100%, but can also be smaller.

Claims (11)

Device for determining the concentrations of various Gases and possibly smoke particles existing components of an exhaust gas mixture Claims: 1. Device for determining the concentrations of different Gases and, if applicable, components of an exhaust gas mixture consisting of smoke particles, with a) an optical radiation source for irradiating the exhaust gas mixture along a measuring section, b) a measuring reflector which reflects the radiation back into itself at the end of the measuring section, c) a photoelectric converter arrangement for generation of measurement signals from those passed through the measurement section and reflected on the measurement reflector Radiation components and d) an evaluation circuit for processing the measurement signals, characterized in that between the measuring section (49) and the measuring reflector (13) a light chopper (10) and at least one selective transmission link in the receiver (8) provided is which suppresses DC voltage components. 2. Apparatus according to claim 1, characterized in that g e k e n n -z e i c h n e t that the light chopper (10) is an electro-optical modulator. 3. Apparatus according to claim 1, characterized g e k e n nz e i c h n e t that the light chopper (10) is a rotating chopper disk. 4. Apparatus according to claim 1, characterized in that g e k e n n -z e i c h n e t that the light chopper (10) is a rotating prism. 5. Apparatus according to claim 1, characterized in that g e k e n n -z e i c h n e t that the light chopper is placed in an intermediate image. 6. Device according to one of the preceding claims, characterized in that g e k e n n n n e i n e t that the converter arrangement (17) is connected to an amplifier (21) with bandpass or High-pass characteristic or connected to a synchronous demodulator is. 7. Device according to one of the preceding claims, characterized in that g I do not know that a second light chopper between the light source and measuring section is arranged and the chopper frequencies of the two chopper different are. 8. Apparatus according to claim 7, characterized in that g e k e n n -z e i c h n e t that a chopper frequency is demodulated and then the demodulated Signal is measured selectively. 9. Apparatus according to claim 7, characterized in that g e k e n n -z e i c h n e t that the input signal is mixed with an auxiliary frequency and the resulting Intermediate frequency is measured selectively. 10. The device according to claim 7, characterized in that g e k e n n -z e i c h n e t that the sum frequency and / or the difference frequency of the two chopper frequencies is measured selectively. 11. The device according to claim 7 to 9, characterized in that g e -k e n n z e i c h n e t that the demodulation and / or the measurement with a synchronous demodulator is made.