AT521524A1 - Gas mixing device for the calibration of gas analyzers - Google Patents

Abstract

The invention relates to gas mixing devices for linearizing or calibrating gas analyzers with a first gas inlet line (10) for a first gas, a second gas inlet line (12) for a second gas, a gas outlet line (48), at least one 3/2-way valve (26) with two inputs (28, 30) and one output (32), the first input (28) with the first gas inlet line (10), the second input (30) with the second gas inlet line (12) and the output (32) with the gas outlet line (48) are fluidly connected, and methods for linearizing or calibrating gas analyzers with such gas mixing devices. According to the invention, the 3/2-way valve (26) is in its first switching position in which the first input (28) and the output (32) are connected and in its second switching position in which the second input (30) and the output ( 32) are connected, energized. For this purpose, the 3/2-way valves (26) are energized before the linearization or calibration of the gas analyzer until a thermal equilibrium is established at the gas mixing device and then by switching the 3/2-way valves (26) various gas mixtures for linearization or calibration Gas analyzer (54) supplied.

Description

SUMMARY

The invention relates to gas mixing devices for linearizing or calibrating gas analyzers with a first gas inlet line (10) for a first gas, a second gas inlet line (12) for a second gas, a gas outlet line (48), at least one 3/2-way valve (26) with two inputs (28, 30) and one output (32), the first input (28) with the first gas inlet line (10), the second input (30) with the second gas inlet line (12) and the output (32) with the gas outlet line (48) are fluidly connected, and methods for linearizing or calibrating gas analyzers with such gas mixing devices.

According to the invention, the 3/2-way valve (26) is in its first switching position in which the first input (28) and the output (32) are connected and in its second switching position in which the second input (30) and the output ( 32) are connected, energized. For this purpose, the 3/2-way valves (26) are energized before the linearization or calibration of the gas analyzer until a thermal equilibrium is established at the gas mixing device and then by switching the 3/2-way valves (26) various gas mixtures for linearization or calibration Gas analyzer (54) supplied.

Fig. 1/24

PI31905AT

AVL List GmbH

-1 Gas mixing device for the calibration of gas analyzers

The invention relates to a gas mixing device for linearizing or calibrating gas analyzers with a first gas inlet line for a first gas, a second gas inlet line for a second gas, a gas outlet line, at least one 3/2-way valve with two inputs and one output, the first input is fluidly connected to the first gas inlet line for the first gas, the second input is fluidly connected to the second gas inlet line for the second gas and the outlet is fluidly connected to the gas outlet line, and a method for linearizing or calibrating gas analyzers with such a gas mixing device.

Such gas mixing devices, which are also referred to as gas dividers, are high-precision devices by means of which precisely defined dilutions of calibration gases can be generated, which can then be made available to an analysis device for calibration, checking or linearization.

These devices are known in particular from the field of exhaust gas analysis technology in motor vehicles. Here, the supply of precisely defined dilutions is essential, as otherwise high percentage errors in the measurements occur due to the sometimes very low concentrations.

In order to obtain this exact mixture, critical nozzles are often used at the individual mixing stages, through which the same volume flow always flows from a certain inlet pressure, which only depends on the smallest opening cross-section of the critical nozzle.

Accordingly, EP 0 690 985 B1 proposes a gas mixing device in which four 3/2-way valves are connected in parallel to one another, each having two inlets and one outlet, a critical nozzle being arranged at the outlet. The smallest free cross section of these nozzles is in a ratio of 2: 1 to the following nozzle / 24

PI31905AT

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-2ausgeführt. Thus, 16 different mixing ratios of the calibration gas and the zero gas can be generated with high accuracy.

However, it is problematic that the mass flow of the gas, which is necessary for determining the mass of pollutants, is dependent on the temperature, even when using critically operated nozzles. It is therefore necessary to ensure thermal stability during calibration in order to eliminate the influence of the temperature, which is not only necessary when using critical nozzles, but is practically always necessary to eliminate the environmental influences on the measurement result. For this reason, in known gas mixing devices, separate cooling or ventilation or a very massive design of the distributor block attempts to prevent the distributor block from heating up by dissipating heat generated in the distributor block as soon as possible and largely preventing the introduction of heat.

However, it has been shown that the measurement results obtained in this way are not always sufficiently precise and that short-term heat compensation can only be achieved with increased effort.

It is therefore the task of providing a gas mixing device for linearizing or calibrating gas analyzers and a method for linearizing or calibrating gas analyzers with such a gas mixing device, with which high thermal stability can be achieved without requiring an increased level of regulation ,

This object is achieved by a gas mixing device for the linearization or calibration of gas analyzers with the features of claim 1 and a method for the linearization or calibration of gas analyzers with such a gas mixing device with the features of claim 13.

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PI31905AT

AVL List GmbH

The inventors have found that the energization of the normally used electromagnetic valves results in an energy input into the gas mixing device, which leads to an increase in the temperature. These valves were energized in one position and held in their other position by a spring force, which resulted in different amounts of energy being introduced into the gas mixing device both in terms of time and space. The fact that the 3/2-way valve is energized in its first switching position, in which a connection is established between the first input and the output, and in its second switching position, in which a connection is established between the second input and the output, lies in the Compared to previously used valves, there is a constant energy input, which means that after a certain settling time, a thermally stable state is established across the entire gas mixing device, in which the amount of heat discharged by convection corresponds to the amount of heat brought in by the energization of the valves, so that a substantially constant temperature distribution is established across the entire device.

Accordingly, in the method according to the invention, the 3/2-way valves are energized before the gas analyzer is linearized or calibrated until a thermal equilibrium is established at the gas mixing device, and then various gas mixtures for linearization or calibration are fed to the gas analyzer by switching the 3/2-way valves. all 3/2-way valves are energized during the entire linearization or calibration period, and the thermal stability state is thus also maintained during the linearization or calibration.

A critically operated nozzle is preferably arranged in an output channel between the output of the 3/2-way valve and the gas outlet line, as a result of which constant volume flows can be set with high precision.

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PI31905AT

AVL List GmbH

In an advantageous embodiment of the invention, the first gas inlet line and the second gas inlet line can each be connected to a plurality of 3/2-way valves connected in parallel, downstream of which a critically operated nozzle is arranged in an outlet channel, the outlet channels opening into a mixing channel which the gas outlet line opens. In this way, many different precise dilutions can be made for linearization or calibration.

In a further embodiment, the critical nozzles downstream of the 3/2-way valves are designed with different narrowest cross sections, the narrowest cross section of each previous nozzle being twice the cross section of the following nozzle. This structure enables a large number of different mixing ratios to be produced, as a result of which a large number of support points are available for linearization, which leads to very precise measurement results in the later operation of the gas analyzer.

In a preferred embodiment of the invention, the gas mixing device has a flow block in which the two gas inlet lines and the mixing channel are formed, with several 3/2-way valves with downstream nozzles being attached to the flow block on both sides of the flow block. Due to the block-shaped design and the solenoid valves arranged on both sides, a constant temperature is established in the entire block after a warm-up time, and thus a thermally stable state in the entire flow area.

In a further advantageous embodiment of the invention, the gas inlet lines are arranged parallel to each other on both sides of the mixing channel in the flow block and the outlet channels with the nozzles are arranged parallel to each other in the flow block. This leads to a further equalization of the temperature distribution and a very small space requirement.

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PI31905AT

AVL List GmbH

It is particularly advantageous if the 3/2-way valves, viewed in the axial direction of the mixing channel, are alternately fastened to the two sides of the flow block, since in this way heat is introduced from both sides and, due to the alternating arrangement, the heat is also introduced via the entire length is made evenly.

In a further preferred embodiment, the smallest nozzle cross section of the critically operated nozzles, viewed in the flow direction of the mixing channel, decreases, so that the largest gas stream remains in the mixing channel for a longer time, as a result of which heat transfer to the entire flow quantity is largely ensured.

The distance of the 3/2-way valves to one another preferably decreases when viewed in the flow direction of the mixing channel. This means that more heat is introduced via the valves in the downstream area of the flow block, since there is a higher temperature gradient to the environment, which would otherwise lead to cooling.

Control valves are preferably arranged in the gas inlet lines, via which a carrier gas and a calibration gas can be supplied to the 3/2-way valves. In this way, a space-optimized gas mixing device is created, into which precisely controllable amounts of gas can be fed for linearization or calibration.

It is particularly advantageous if a pressure sensor is arranged upstream of the 3/2-way valves in the gas inlet lines, so that errors in the gas mixture due to pressure fluctuations can be avoided or eliminated or the gases can be regulated to a constant pressure by means of the control valves in order to prevent errors avoid and provide the nozzles with sufficient pressure to produce a constant volume flow.

Accordingly, it also makes sense if a control valve and a pressure sensor are arranged in the gas outlet line downstream of the mixing channel in order to always have a mixed gas with a / 24 around the gas analyzers

PI31905AT

AVL List GmbH

-6 constant temperature and a constant pressure, which enables a very precise check or linearization.

In a further embodiment of the method according to the invention, the switching of the 3/2-way valves between the two positions is carried out by reversing the voltage and the 3/2-way valves are kept in their respective positions by constant energization. This means that there is a constant current flow in the electromagnet and only the polarity of the electromagnet is changed for positioning, as a result of which heat is continuously introduced and a thermal equilibrium is established.

A gas mixing device for linearizing or calibrating gas analyzers is thus created, with which the gas analyzer to be supplied with gas can always be provided with a calibration gas with very precise mixing ratios and under almost constant conditions with regard to pressure and temperature, in the gas mixing device a steady state with regard to these physical quantities is produced.

Non-limiting exemplary embodiments of a gas mixing device according to the invention and the corresponding method for linearizing or calibrating a gas analyzer with such a gas mixing device are shown in the figures and are described below with reference to the figures.

FIG. 1 shows a flow diagram of a gas mixing device according to the invention for the linearization or calibration of a gas analyzer.

FIG. 2 shows a three-dimensional perspective view of an alternative gas mixing device according to the invention.

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FIG. 3 shows a three-dimensional perspective view of a section of the gas mixing device according to the invention from FIG. 2.

FIG. 4 shows a three-dimensional perspective view of a section of the gas mixing device according to the invention from FIG. 2 with a section through the flowed-through part of a 3/2-way valve of the gas mixing device.

The gas mixing device shown in FIG. 1 consists of a first gas inlet line 10, which serves as a calibration gas feed line, and a second gas inlet line 12, which serves as a carrier gas or zero gas feed line. A control valve 14, 16 is arranged in each case in the gas inlet lines 10, 12 in order to regulate a defined gas flow in the gas inlet lines 10, 12. For this purpose, a pressure sensor 18, 20 is arranged in the gas inlet lines 10, 12 downstream of the control valves 14, 16, via which the pressure in the gas inlet lines 10, 12 is measured and made available to a control unit via which a feedback to the control valves 14, 16 takes place so that the pressure in the gas inlet lines 10, 12 can be regulated to a defined value.

Four gas supply lines 22, 24 branch off from the gas inlet line 10 and the gas inlet line 12, which lead to a 3/2-way valve 26, each of the four 3/2-way valves 26 having two inlets 28, 30, each of which is the first inlet 28 is fluidly connected to the first gas inlet line 10 via one of the gas supply lines 22 and the second input 30 is connected to the second gas inlet line 12 via one of the gas supply lines 24. Each of these 3/2-way valves 26 has an outlet 32 through which, depending on the position of a regulating body 34 of the respective 3/2-way valve 26, either a carrier gas flow or a calibration gas flow from the respective inlet 28, 30 in the direction of a critically operated nozzle 36, 38, 40, 42 flows.

The critically operated nozzles 36, 38, 40, 42 are each arranged in an outlet channel 44 and have different narrowest / 24th

PI31905AT

AVL List GmbH

-8 cross-sections, each of which is graduated in a ratio of 1: 2, that is, in the four existing nozzles, in a ratio of 1: 2: 4: 8. Since the same volume flow always flows through these nozzles 36, 38, 40, 42 from a certain inlet pressure, which can be ensured by the control valves 14, 16 with the pressure sensors 18, 20, which is only from the smallest opening cross section of the respective critical nozzle 36, 38, 40, 42 is dependent, clearly defined volume flows of the carrier gas and the calibration gas are likewise generated in a ratio of 1: 2 at the different output channels downstream of the nozzles 36, 38, 40, 42. Accordingly, it is possible in this way to generate 14 different defined mixing ratios between the two clean gas streams by changing the positions of the 3/2-way valves accordingly.

For this purpose, the four outlet channels 44 open one after the other into a mixing channel 46, which in turn opens downstream of the four ports into a gas outlet line 48, in which a pressure sensor 50 and a control valve 52 are also arranged. The gas outlet line 48 can be fluidly connected via the control valve 52 to a gas analyzer 54, to which different mixing ratios can be made available for linearization, the evaluation results of which serve as support points for a later exhaust gas analysis of the gas analyzer 54.

Since the nozzles 36, 38, 40, 42 only ensure defined volume flows, it is necessary to keep the temperature in the gas mixing device constant for reproducible results. For this reason, the 3/2-way valves 26 are designed as continuously energized solenoid valves, the switching of which takes place by reversing the current direction or reversing the voltage and which are also energized continuously in their two end positions. Through this design of the 3/2-way valves 26, a continuous energy and thus heat flow is introduced into the system by the current supply. After a certain warm-up time, there is a temperature difference to the environment, which leads to a stationary / 24

PI31905AT

AVL List GmbH

Condition of the gas mixing device is reached so that the amount of heat supplied by the current supply corresponds to the amount of energy introduced by convection and radiation. Thus, a gas flow with the same temperature is always supplied to the nozzles 36, 38, 40, 42, so that a very precise gas mixture is made possible without temperature differences having to be taken into account when determining the concentration.

A particularly favorable form of implementing this gas mixing concept is shown in FIGS. 2 to 4. The first gas inlet line 10, the second gas inlet line 12 are at least partially formed, the gas supply lines 22, 24, the outlet channels 44, the critically operated nozzles 36, 38, 40, 42 and the mixing channel 46 in a flow block 56 on which the third / 2-way valves 26 are fastened by means of screws 58. In FIG. 3 it can be seen that the 3/2-way valves 26, viewed in the axial direction of the mixing channel 46, are alternately fastened to the two sides of the flow block 56, the distance between the total of eleven 3/2-way valves from one another with increasing distance from the gas inlets 60, 62 drops.

In FIG. 4 it can be seen that the mixing channel 46 is arranged in the flow block 56 between the two gas inlet lines 10, 12 and aligned parallel to them. The gas supply lines 22, 24 and the outlet channel 44 branch off from the gas inlet lines 10, 12 and the mixing channel 46 at a 90 ° angle and are also aligned parallel to one another. They are extended in a valve plate 64 which bears against a valve seat body 66 which has two valve seats 69, 70 which limit the gas supply lines 22, 24 and to which the rocker-shaped control body 34 can be lowered, which, depending on the position, either on the first valve seat 68 or rests on the second valve seat 70 and thus either blocks the calibration gas flow or the carrier gas flow in the 3/2-way valve 26 or releases the other one to the outlet channel 44. An electromagnetic actuator 68/24 is located on the valve seat body 66

PI31905AT

AVL List GmbH

-10 flanged, at the end of which the control body 34 is fastened in the form of a sealing membrane. The valve seat body 66 is sealed off from the valve plate 64 via three O-rings 71 surrounding the gas supply lines 22, 24. Correspondingly, the screws 58 for fastening penetrate the valve plate 64, the valve seat body 66 and a flange section of the electromagnetic actuator 68 and are screwed into the flow block 56.

For linearization or calibration, a warm-up phase is initially initiated, in which the 3/2-way valves 26 are energized as desired until the thermal equilibrium is reached, with or without opening the gas inlet lines. This remains during the linearization or calibration, since a constant amount of energy is introduced into the system and a constant amount of energy is also removed from the gas mixing device by convection and heat radiation. During the gas mixing, this leads to constant temperature distributions in the flow block 56 and constant temperatures of the mixed gas in the nozzles 36, 38, 40, 42 in front of the gas outlet line 48, from where the respective mixed gas flow with a defined mixing ratio is fed to the gas analyzer 54. External cooling devices for maintaining a constant temperature, which must be subjected to precise control, are accordingly no longer required.

It should be clear that the scope of the present main claim is not limited to the exemplary embodiments described. In particular, other devices for maintaining a constant volume flow can be provided or the channels can be realized in a different form than in the flow block. Likewise, different or a different number of electrical valves can be used as mixing valves, which only have to be designed as permanently energized valves.

Claims (14)

P A T E N T A N S P R Ü C H E 1. Gas mixing device for linearization or calibration of gas analyzers with a first gas inlet line (10) for a first gas, a second gas inlet line (12) for a second gas, a gas outlet line (48), at least one 3/2-way valve (26) two inputs (28, 30) and one output (32), the first input (28) being fluidly connected to the first gas inlet line (10) for the first gas, the second input (30) to the second gas inlet line (12) for the second gas is fluidly connected and the outlet (32) is fluidly connected to the gas outlet line (48), characterized in that the 3/2-way valve (26) in its first switching position, in which a connection between the first inlet (28 ) and the output (32) is produced and in its second switching position, in which a connection between the second input (30) and the output (32) is established, is energized. 2. Gas mixing device for the linearization or calibration of gas analyzers according to claim 1, characterized in that a critically operated nozzle (36,) in an output channel (44) between the outlet (32) of the 3/2-way valve (26) and the gas outlet line (48). 38, 40, 42) is arranged. 3. Gas mixing device for linearization or calibration of gas analyzers according to one of the preceding claims, characterized in that 12/24 PI31905AT AVL List GmbH -12 the first gas inlet line (10) and the second gas inlet line (12) can each be connected to a plurality of 3/2-way valves (26) connected in parallel, downstream of each of which a critically operated nozzle (36, 38, 40, 42) in an output channel ( 44) is arranged, the output channels (44) opening into a mixing channel (46) which opens into the gas outlet line (48). 4. Gas mixing device for linearization or calibration of gas analyzers according to claim 3, characterized in that the critically operated nozzles (36, 38, 40, 42) downstream of the 3/2-way valves (26) are formed with different narrowest cross sections, the narrowest cross section each previous nozzle (36, 38, 40) corresponds to twice the cross-section of the following nozzle (38, 40, 42). 5. Gas mixing device for linearization or calibration of gas analyzers according to claim 3 or 4, characterized in that the gas mixing device has a flow block (56) in which the two gas inlet lines (10, 12) and the mixing channel (46) are formed, on both sides the flow block (56) a plurality of 3/2-way valves (26) with downstream nozzles (36, 38, 40, 42) are attached to the flow block (56). 6. Gas mixing device for the linearization or calibration of gas analyzers according to claim 5, characterized in that the gas inlet lines (10, 12) are arranged parallel to each other on both sides of the mixing channel (46) in the flow block (56) and the output channels (44) with the nozzles ( 36, 38, 40, 42) are arranged parallel to one another in the flow block (56). 13/24 PI31905AT AVL List GmbH 7. Gas mixing device for linearization or calibration of gas analyzers according to claim 5 or 6, characterized in that the 3/2-way valves (26) viewed in the axial direction of the mixing channel (46) are alternately attached to the two sides of the flow block (56). 8. Gas mixing device for linearization or calibration of gas analyzers according to claim 5 to 7, characterized in that the smallest nozzle cross section of the critically operated nozzles (36, 38, 40, 42) decreases when viewed in the flow direction of the mixing channel (46). 9. Gas mixing device for linearization or calibration of gas analyzers according to claim 5 to 8, characterized in that the distance of the 3/2-way valves (26) to each other in The direction of flow of the mixing channel (46) decreases. 10. Gas mixing device for linearization or calibration of gas analyzers according to one of the preceding claims, characterized in that in the gas inlet lines (10, 12) control valves (14, 16) are arranged, via which a carrier gas and a calibration gas the 3/2-way valves (26) can be fed. 11. Gas mixing device for linearization or calibration of gas analyzers according to claim 10, characterized in that 14/24 PI31905AT AVL List GmbH A pressure sensor (18, 20) is arranged upstream of the 3/2-way valves (26) in the gas inlet lines (10, 12). 12. Gas mixing device for linearization or calibration of gas analyzers according to one of the preceding claims, characterized in that a control valve (52) and a pressure sensor (50) are arranged in the gas outlet line (48) downstream of the mixing channel (46). 13. A method for the linearization or calibration of gas analyzers with a gas mixing device according to one of the preceding claims, characterized in that before the linearization or calibration of the gas analyzer (54) the 3/2-way valves (26) are energized until a thermal equilibrium on the gas mixing device and then, by switching the 3/2-way valves (26), various gas mixtures for calibration are fed to the gas analyzer (54), all 3/2-way valves (26) being energized during the entire linearization period. 14. A method for linearizing or calibrating gas analyzers according to claim 13, characterized in that the switching of the 3/2-way valves (26) between the two positions takes place by voltage reversal and the holding of the 3/2-way valves (26) in their position by constant energization.