FI73526C - KONCENTRATIONSMAETANORDNING. - Google Patents

Description

TECHNICAL FIELD The present invention relates to a measuring device for measuring the concentration of particles as they are passed through a tube in a liquid. The measuring probes are then placed in the wall of the tube to be in contact with the liquid.

10 Background Art

When measuring the concentration of particles in predominantly stationary liquids, it is known, for example in connection with the treatment of social and industrial wastewater, to use photometric measurement with a nice infrared light (IR), as shown in Swedish patent 382,116.

The known method has its limitations and then the liquids which stand first and foremost and the substantially constant temperature. At variable temperatures, the known method may give rise to substantial measurement errors. In addition, the known method suffers from disadvantages such that the measuring probes have to clean the particle deposits after a short period of use and that significant changes and additions have to be made if the device used in the method 25 can be used to measure particles in flowing water such as pulp transfer equipment.

Disclosure of the Invention 30

The present invention, as defined below in the characterizing part of the following claim 1, avoids the above-mentioned disadvantages and difficulties.

o c

With the present measuring device, it has now been possible to show that the measurement with the present measuring probes is well suited for use with a liquid containing particles, which is fed through a pipeline. Experts have previously argued that, for example, measuring the fiber concentration of the feedstock using 40 IR probes would be impossible or would require at least continuous repetitive cleaning of the 73526 2 measuring probes. However, this is an aspect that is completely discarded by the present invention. By changing the cross-sectional area in the tube, it has been shown that the surfaces of the measuring probes facing the liquid remain automatically clean.

With the measuring probes connected to the reference circuit which are also connected to the reference device consisting of the reference measuring element, which are in thermally conductive contact with the liquid supply tube, the measuring device according to the invention has also avoided the previously difficult problem of measuring circuit instability when supplying such liquids.

This reference device has a function combined with the design of the measuring area and is surrounded by a jacket which surrounds the liquid supply pipe and the measuring probes.

The measuring device according to the invention has use in both the process industry and the VA area. The device is intended for accurate concentration measurement, for example in the paper and screening industry, where the measurement can be made before pressure silos and vortex cleaners, and for pulp before the paper machine headbox and for return water for both dilution and fiber recovery. In the VA range, the device is useful for measuring sludge content and turbidity, as well as for measuring the content of suspended material 25, for example in the reject waters of dewatering centrifuges or other mechanical dewatering machines.

The measurement principle is based on the particle's ability to absorb and reflect light.

30

To achieve the highest possible dynamics, some of the electronics are mounted on the sensor. The measurement is performed with IR light at a measuring distance of 20 nm. The IR light pulses with very short pulses and has a rather high light intensity, which is possible by means of the shortest possible pulses and the long interval between pulses. The high light intensity has the advantage that the different measuring ranges can be utilized by a simple switching of the amplifier which is included in the electronic circuit. Since the light input from the IR diode is strongly temperature dependent, this is compensated by a separate reference system in the sensor. This also compensates for use in other components as well as any incident stray light.

The sensor measurement signal consists of a pulse whose height is proportional to the concentration. This pulse can be converted to a DC voltage in the collecting and holding circuit, which is at the same time connected to the integration time. This has a fixed time around its measured value, and a settable time to dampen larger concentration changes.

10 After the collecting and holding circuit, the signal continues to the MAX and ja setting, directly or via a log amplifier. The output stage gain can be changed with the toggle switch. The digital measured value sensor shows 0-100% of the set range, regardless of which output signal is selected.

15

Recommended embodiment

The measuring device according to the invention will be described in detail together with the preferred embodiment and with reference to the accompanying drawings, in which

Figure 1 shows the sensor of a preferred embodiment of the invention from the front, seen from the inlet direction of the liquid supply direction, 2

Figure 2 shows a section H-H according to Figure 1,

Fig. 3 shows a block diagram of the popular electrical connection of the transmitters and measured value detectors included in the sensor, and Fig. 4 shows a graph diagram of, for example, various possible measuring ranges that can be connected.

The measuring device according to the invention comprises a sensor 1, which in the preferred embodiment according to Figures 1 and 2 comprises a tube 2 for supplying a liquid containing particles q q, where the measurements are to be performed. The pipes 2 are provided with a connecting device 3, 4 for connection to a pipeline (not shown). The measuring area has a deformed cross-sectional area across the pipe 2, but preferably has the same size. Thus, in the 40 preferred embodiments, the cross-sectional area of the tube 2 changes from a normally circular cross-section in the connecting device 3, 4 to a substantially rectangular cross-section 5, which is best seen in Figure 1. The change from a circular to a rectangular cross-section 5 times by squeezing together an initially circular tube.

The rectangular region 5 of the opposite walls 6, 7 of the pipe 2 has openings for the placement of the measuring paths 8, 9. The measuring probes 8, 9 completely fill the openings in the walls 6, 7 10 of the pipe 2 and their inwardly facing sonar surfaces 10, 11 facing the liquid to be fed are substantially flush with the inner surface of the walls 6, 7 of the pipe 2.

The measuring area with its rectangular areas 5 and measuring probes 8, 9 is surrounded by a jacket 12. Here the jacket 12 is preferably tubular and its longitudinal axis extends perpendicular to both the longitudinal axis of the tube 2 and the axis formed by the measuring probes 8, 9. The jacket 12 has openings for the insertion and inspection of the measuring probes 6, 9, which, as shown 20, can protrude out of the jacket 12.

The jacket 12 further includes a reference device 13, 14 formed by a measuring member corresponding to the measuring probes 8, 9, but not measuring via a liquid like the measuring probes but through an unobstructed path in the jacket. The reference device 13, 14 is in thermally conductive contact with the tube 2 and may be located below the tube 2 (as shown in Figure 2) or, preferably, above the tube 2.

The housing 12 also includes at least a portion of the electronic circuitry used to process the signals obtained from the measuring probes 8, 9 and the reference device 13, 14. Both the measuring probes and the reference device are preferably of the IR type, although other types as such operate with visible light or ultrasound may be useful in the practice of the present invention. A preferred embodiment of the electronic circuit will be described below with reference to Figure 3.

It can be seen from the block diagram of Fig. 3 that the measuring probes 40 and the reference device 13, 14 consist of IR elements, more specifically the IR diodes of the soap can be advantageously used. Furthermore, the transmitter 8 of the measuring probes is used as a member which is common with the transmitter 13 of the reference device. Thus, the IR diode 8, 13 can be used as a common transmitter in both the measuring range M and the reference range R, whereby different light paths M and R can, for example, leave fiber optics connected to the diode 8, 13. Another feasible solution is two exactly identical IR diodes 8, 13, which thus form the transmitter of the measuring interval M or the transmitter of the reference interval R, respectively.

10

The detector 9 of the measuring probes is, like the detector 14 of the reference device, a separate photodiode. Both of these photodiodes are of the same type and are each connected to a temperature compensating circuit 15-18 or 19-22 identically shaped. Thus, the output of the photodiodes 9, 14 is connected to the amplifiers 15, 19, respectively, which supply the integrator 17, 21 via the holding circuit 16, 20. The combined signal is again connected via the resistor 18, 22 to the input of the amplifier 15, 19. The diode is relatively temperature dependent but the compensating circuits 15-18 and 20 19-22 achieve a stabilizing operation so that the output signal level of the amplifiers 15, 19 is kept constant despite the temperature fluctuations that may occur around the detectors 9, 14 and in the liquid, which particle concentration should be measured. in air in an unobstructed reference path and in a tube with which the reference-25 reference device is in thermal contact. These compensating circuits 15-18, 19-22 also achieve a stabilizing action in the event of possible interference light, which may encounter detectors 9, 14. Thus, each slower change in the output signal from detectors 9, 14 must be smoothed so that a stable reference level is reached by the preamplifiers 15, 19 outlets.

The signal transmitter or transmitters 8, 13 arranged for this or those measurement and reference signals are fed from the oscillator 23. The oscillator 23 generates a pulse signal S well with 35 short-term pulses and relatively long intervals between pulses. This ensures that a high light intensity can be achieved without damaging the IR diode 8, 13 due to its own heating. When the transmitter 8, 13 is similarly made of a diode, it is also prone to temperature fluctuations. Its variations are compensated by a circuit 24-26 consisting of a comparator 24 followed by an integrator 25 and a power gain stage 26. The comparator 24 is supplied with a pulse signal S from an oscillator 23 and an output signal SR from a reference device amplifier 15. This output signal SR is also a pulse signal and is directly dependent on the magnitude of the light pulses transmitted by the transmitter 8, 13 via the reference slot R. The magnitude of the light pulses emitted by the transmitter 8, 13 is adjusted by the comparator 24 and the power amplifier stage 26 so that the pulse signals S and SR become equal. This thus achieves constant light pulses regardless of the temperature variations in the transmitter 8, 13. Also if the transmitter is made of two separate diodes 8 and 13, as mentioned above, both diodes 8 and 13 have light pulses with a constant value, since both diodes 8 and 13 are electrically connected in series and mechanically connected to the same substrate and thus are affected by the same temperature variations.

The light pulses transmitted from the transmitters 8, 13 at a constant value are also captured by the detectors 9 after ignoring the measurement interval M, i.e.; after passing through the liquid and the particles therein. particle concentration

O Q

when varying, the light pulses received from the detector 9 vary depending on the luminance of the particles. As a result, the output signal at the preamplifier 19 of the measurement detector 9 varies depending on the particle concentration of the liquid.

Since the temperature compensated circuits 15-18, 19-22 of the detectors 9, 14 would not be affected by the operating signals SR and the holding circuits 16, 20 are connected between the amplifier 15, 19 and the integrator 17, 22 in each temperature compensated circuit 15-18, 19-22. This holding circuit 16, 20 is controlled by the output signal S of the oscillator 23, so that the operating signals SR, are grounded when present in the holding circuit 16, 20. A further reason that the operating signals SR are not reconnected to the inputs of the amplifiers 15, 19 is that the temperature compensated circuits 15-18, 19-22 operation is slow. 1 40

The operating signal taken from the output of the amplifier 19 of the measuring detector 9 thus gives an accurate measure of the concentration of particles in the liquid which is fed through the pipe 2 (Fig. 2). This signal is therefore available in different processes for different purposes.

73526

For measurement purposes, but also for applications, it may be desirable to have a smoothly flowing output signal instead of a pulsating output signal. By applying the output signal to the collecting and holding circuit 27, which is controlled by the signal S-5 1a of the oscillator 23, a logarithmically variable signal is obtained. If a linearly variable signal S1n is desired, the signal from the collecting and holding circuit 27 is fed to a logarithmic amplifier 28.

The toggle switch 29 can alternatively supply a signal or a signal S ^ n · 10 to the meter 30

The collecting and holding circuit 27 can be made of a field power transistor FET and the meter 30 can be made of a digital indicating meter.

The output signal of the amplifier of the measuring detector 9 can optionally be feedback to its input via different resistors 31, so that different measuring ranges Τ-33Γ are obtained. Thus, for example, there can be four different measuring ranges. Figure 4 shows by means of a curve diagram how the measuring range can be shifted 20 in the case of a partly logarithmic signal and partly a corresponding linear signal S ^ n · In this case, the range X corresponds to the max. Connected to the feedback branch of the preamplifier 17. maximum resistance value while the area UT corresponds to the direct connection of the output signal to the input of the preamplifier 19.

25

As can be seen from the above description, this refers exclusively to an embodiment of the present invention, which can therefore be formulated in different ways without departing from the spirit of the invention. Thus, for example, the cross-sectional area 30 of the tube 2 can be changed to a shape other than rectangular or larger than the surface area of the tube. The cross-sectional area can also be changed by placing the inner part in an expanded part of the pipe or by changing the design of the pipe wall affecting the fluid supply. With regard to the measuring probes and the reference device, it has already been stated O c that these are not limited to the use of IR light. Of course, the electronic circuit described for the IR components can also be designed in different ways without departing from the idea of the invention. For example, the circuit can be shaped with a toggle switch member solely to examine each part of the curve, for example, an interval of 60-70% of the ko-40 ko measurement range. It is further possible to introduce the control member 8 73526 to set the integration time so as to obtain a calm indication on the meter 30.

It will be apparent from the foregoing that the invention cannot be construed as limited to the preferred embodiment set forth above and shown in the drawings, but may be directed to non-specific designs within the scope set forth in the following claims.

Claims (7)

73526 A measuring device for measuring the concentration of particles transferred in a liquid through a tube (2), the measuring probes (8,9) being arranged in the wall of the tube in contact with the liquid in a part of a transfer tube with a substantially rectangular cross-section, characterized in that the transfer tube (2) the cross-sectional area continuously changes from a circular cross-section to a substantially rectangular cross-section, wherein the flow-through cross-section (5) of the transfer tube at the measuring probes is substantially equal to the cross-section at the transfer tube (2) before and after the measuring device; ) is surrounded by an outer liner (12) 15 to cover the measuring probes and the reference device (13,14). Measuring device according to Claim 1, characterized in that the jacket (12) is tubular with a circular shape:. with cross - sections whose longitudinal axis is perpendicular to. 20 against the tubes (2) where the liquid is conveyed and partly against the longitudinal axis of the measuring probes (8.9), which measuring probes can be • · · released from outside the jacket. • · · Measuring device according to Claim 1 or 2, characterized in that the measuring probes (8, 9) consist of an IR transmitter (8) and an IR detector (9), which is supplied by a pulsating device. energy, wherein the reference device (13, 14) has a corresponding: an IR transmitter (13) and an IR detector (14) which are supplied with a pulse; energy from a power supply (23) common to the measuring probes and the reference device. :. * V Measuring device according to one of the preceding claims, characterized in that each measuring probe (8, 9) has a surface (10, 11) which is in contact with a liquid, which surface forms a tube (10) of the same surface. 2) with the inner surface (6,7). 73526 Measuring device according to Claim 1 or 3, characterized in that the measuring probes (8, 9) and the reference device (13, 14) are connected to a temperature-compensated electronic circuit (Fig. 3) for digitally transmitting the obtained measured value of the concentration of particles in the liquid. Measuring device according to claim 3, characterized in that the transmitter (8, 13) of the measuring probes and the reference device is a common member arranged to supply the detector (9) of the measuring probes 10 through the liquid and particles and the detector (14) of the reference device via the reference path (R). Measuring device according to claim 5, characterized in that the power supply (23) is arranged to supply the transmitters 15 (8, 13) via a power amplifier circuit (24-26) comprising a comparator (24) arranged to compare the pulse output from the power supply. energy to the pulsating energy generated by the reference device detector (14) and, after amplification in the associated temperature-compensated circuit (15-18), to be fed 20 si to said comparator (24), the output signal of which, after integration and amplification, is arranged to be supplied * »· transmitters (8,13), wherein the concentration measurement signal - *. *. · * is arranged to be taken from the output of the amplifier (19) connected to the measurement probe detector (9) in the associated temperature-compensated circuit (19-20). P- • * · · · P- • * • · · P- • * • · · * »m * * m Ψ • ·» »· • · · * * · »· 73526