METHOD AND ARRANGEMENT FOR THE ANALYSIS OF GAS CHARACTERISTICS

Abstract

Detection of gas characteristics, especially the detection of the gas composition, the temperature and/or humidity of a gas, by measuring the speed of sound with a sound sender and a sound receiver both mounted on common structure. A method for determining the humidity of the scavenge air of an internal combustion engine. A speed of sound based gas sensor arrangement adapted to measure gas characteristics, especially the gas composition, the temperature and/or the humidity of a gas, including a sender, a receiver and a signal processing unit. The speed of sound is determined by driving the sender and receiver at different operation cycles in order to differentiate between the different travel times of the sound through the gas and the common structure of solid material.

Claims

1. A method for measuring a speed of sound in a gas for detection of gas characteristics, with a sound sender and a sound receiver both mounted on a common structure, comprising: providing the structure having a speed of sound which is higher than the speed of sound in the gas, arranging the sender and the receiver on the structure, operating the sender during at least one period of time in an “on”-status such that the sender sends an acoustical signal and operating the sender during at least one period of time in an “off”-status such that the sender does not send an acoustical signal, operating the receiver in an “off”-status for at least one period of time during the “on”-status of the sender and operating the receiver in an “on”-status for at least one period of time during the “off”-status of the sender, integrating the signal of the receiver by an amplifier, calculating the speed of sound and determining based on the speed of sound the said characteristics of the gas.

2. The method according to claim 1, comprising starting the “on”-status of the receiver with a delay after the end of the “on”-status of the sender.

3. The method according to claim 1, wherein the duration of the “on”-status of the receiver corresponds to the travel time of the sound from the sender to the receiver through the gas and/or the duration of the “on”-status of the sender corresponds to the travel time of the sound from the sender to the receiver through the gas.

4. The method according to claim 1, comprising integrating the signal of the receiver by the amplifier over extended periods of time.

5. The method according to claim 1, comprising calculating the characteristics of the gas from the phase angle difference between the sender excitation and the receiver signal.

6. The method according to claim 1, comprising providing a mechanical structure having a speed of sound being at least five times higher than the speed of sound in the gas.

7. The method according to claim 1, comprising arranging the sender and the receiver on that structure such that the sound emitted by the sender reaches the receiver via an acoustical reflector.

8. The method according to claim 1, comprising arranging the sender and the receiver within a distance of less than 10 mm.

9. A method comprising determining humidity of an engine scavenge air using the method of claim 1.

10. A speed of sound based gas sensor arrangement adapted to measure gas characteristics according to the method as recited in claim 1.

11. A speed of sound based gas sensor arrangement adapted to measure gas characteristics, comprising a sound sender, an acoustical receiver and a signal processing means, wherein the sound sender and the acoustical receiver are both mounted on a common structure, wherein the signal processing means operates the sender for at least one period of time in an “on”-status such that the sender sends an acoustical signal and the signal processing means operates the receiver for at least one period of time in an “off”-status such that the sender does not send an acoustical signal, wherein the signal processing means operates the receiver in an “off”-status for at least one period of time during the “on”-status of the sender and in an “on”-status for at least one period of time during the “off”-status of the sender, and wherein the signal processing means, especially a microprocessor of the signal processing means, integrates the signal of the receiver, calculates the speed of sound and determines based on the speed of sound gas characteristics and provides a respective output signal.

12. The speed of sound based gas sensor arrangement according to claim 11, wherein the acoustical signal from the sender reaches the receiver via an acoustical reflector, wherein the acoustical reflector is a wall of a pipe or a wall of a housing of a chamber and that the gas to be measured is within that pipe or chamber.

13. The speed of sound based gas sensor arrangement according to claim 11, wherein the sound sender and the acoustical receiver are both mounted side by side on the common structure within a distance of less than 10 mm.

14. The speed of sound based gas sensor arrangement according to claim 11, wherein the measured gas characteristics is at least one of gas composition, humidity and temperature.

15. The method according to claim 1, wherein the measured gas characteristics is at least one of gas composition, humidity and temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The figures show:

[0032] FIG. 1 a principle depiction of a gas sensing arrangement comprising a sender and a receiver on a common structure and reflection means arranged apart from the sender and the receiver such that the sound excited by the sender travels via the reflection means to the receiver through the gas for providing a gas-borne signal,

[0033] FIG. 2 another principle depiction of a gas sensing arrangement comprising a sender and a receiver on a common structure wherein sender and receiver are arranged such that the sound travels directly from the sender to the receiver through the gas between the sender and the receiver for providing a gas-borne signal,

[0034] FIG. 3 the principle depiction of FIG. 2 together with a block diagram of a signal processing unit comprising signal processing means, and

[0035] FIG. 4 a diagram of the cycle times of the sender and the receiver with different receiver cycle times.

DETAILED DESCRIPTION

[0036] The principle of the common structure with the sender and the receiver with or without reflection means can be used in all applications which require a reliable system in extreme environment conditions for systems, such as for example in combustion engine exhaust applications or applications which require measurements across large temperature ranges.

[0037] FIG. 1 shows a mounting structure 3 with a sender 1 and a receiver 2 mounted on that structure 3. Sender 1 and receiver 2 are mounted such that the sound propagation 4 from the sender 1 to the sender 2 travels via an acoustic reflector 6 before reaching the sender 2. That sound provides a gas-born signal. The sound propagation 5 of the sound provided by the sender 1 travels via the structure 3 to the receiver 2 thereby providing a structure-born signal.

[0038] FIG. 2 shows a mounting structure 3 in which the sender 1 and the receiver 2 mounted on that structure 3 are arranged in a face to face position wherein the sound propagation 4 is directly from the sender 1 to receiver 2 without a reflector in the sound path. In contrast to the arrangement of FIG. 1, sender 1 and receiver 2 are arranged with a much larger distance between them. The distance between the sender 1 and receiver 2 in the arrangement according to FIG. 1 is less than 10 mm, preferably around 4 mm, whereas the distance in the arrangement of FIG. 2 is in the order of 50-100 mm. It is important that the propagation times, i.e. time that the sound needs from the sender 1 to the receiver 2 via the different media (gas or solid material), differ significantly in order to determine the speed of sound of the gas after processing the received signals with a sufficient accuracy. Similar to FIG. 1, the sound traveling directly through the gas from the sender 1 to the receiver 2 provides the gas-borne signal and the sound propagation 5 through the structure from the sender 1 to the receiver 2 provides the structure-borne signal. The acoustical reflector 6 can be a wall of a pipe or a wall of a housing of a chamber and the gas to be measured is within that pipe or chamber (not depicted).

[0039] In FIG. 3 a block diagram is shown depicting a signal processing unit 7 comprising a microprocessor 13 and a sound function generator 8 which provides an ultrasound in this embodiment. The sound function generator 8 is connected with the sender 1. The receiver 2 is connected with a receiver pre-amplifier/AD-converter 10 of the signal processing unit 7. The signal processing unit 7 also comprises a switching function generator which controls the sound function generator 8 and the receiver pre-amplifier/AD-converter 10 in view of their duty cycle. The sound function generator 8 is connected with a lock-in amplifier 11 as well as the receiver pre-amplifier/AD-converter 10. The sound function generator 8 provides the lock-in amplifier 11 with a respective reference signal. The lock-in amplifier 11 determines the phase angle between the reference signal delivered from the sound function generator 8 and the receiver signal from the receiver pre-amplifier/AD-converter 10. A microprocessor 13 of the signal processing unit 7 reads the output signal from the lock-in amplifier 11 as well as from an external temperature measurement device 12 and provides a humidity value output 14 in form of a respective signal for further processing. In another advantageous embodiment, the lock-in amplifier 11 can be integrated digitally within the microprocessor 13.

[0040] In an exemplary embodiment, the sender 1 and the receiver 2 as shown in FIG. 1 are mounted very closely (distance of 4 mm) in parallel on the structure 3 made of steel. The sound of speed in steel is approximately 4,000 m/s, which means that any structure-borne sound takes 1 μs to travel from the sender to the receiver.

[0041] Through the gas, the sound will travel via the acoustical reflector 6 over a total distance of 40 mm. With a sound of speed in the gas in the order of 400 m/s, the gas-borne sound takes 100 μs to travel from the sender 1 to the receiver 2.

[0042] Both contributions can therefore be separated in time as shown in FIG. 4. In that figure the first diagram shows the duty times of the sender 1 over time. The second and middle diagram shows the duty time of the receiver 2 without delay with respect to “on”-status of the sender 1, whereas in the third and lowest diagram shows the duty time of the receiver 2 is delayed in respect to the shut-off of the sender 1. In the above example with the mentioned dimensions and material, the sender 1 is operated during 100 μs, while the input from the receiver 2 to the amplifier 10 is switched off. During the next 100 μs, the sender 1 is switched off while the signal of the receiver 2 is measured by the amplifier 10. As the last structure-borne sound will reach the receiver 2 1 μs after the sender 1 has been switched off, the structure-borne contribution to the receiver signal has been reduced to 1%, if both contributions have the same amplitude. The structure-borne contribution can be reduced further by introducing a delay of some few microseconds between switching off the sender 1, and switching on the receiver 2 as shown in the lowest diagram of FIG. 4. Such a delay might be necessary if internal reflections of the sound within the structure 3 delay the transition time of the structure-borne sound.

[0043] As the overall noise level of the measurement strongly depends on over how many signal oscillations the amplifier can integrate, the << on >> time of the receiver 2 should correspond to the time of travel of the gas-borne sound. For the same reason, the << on >> time of the sender 1 should span the same amount of time, so that the duty cycles of sender 1 and receiver 2 are both 50% with a phase shift of 7C.

[0044] At an operational frequency of 50 kHz, the amplifier 11 will therefore integrate the receiver's signal over 5 periods. However, with a lock-in amplifier 11 as used it is possible to integrate the receiver signal continuously over extended periods of time. The amplitude measured by the lock-in amplifier 11 will be half of a continuous signal, whereas the phase angle information is entirely maintained. In this case, the function generator 8 driving the sender 1 must supply a reference signal to the lock-in amplifier 11 all the time.