Measuring and testing – Gas analysis – Detector detail
Patent
1999-06-09
2000-05-02
Williams, Hezron
Measuring and testing
Gas analysis
Detector detail
73 232, 73 2334, 73 3101, 7333505, 324691, 324712, 340634, 422 98, 422 90, 236 44, 236 492, 165249, 237 126, G01N 2712, G01N 100, G01N 3700
Patent
active
060558482
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a device for measuring air quality.
BACKGROUND INFORMATION
In the related art, an analog signal controls a voltage-controlled oscillator (VCO). The voltage-controlled oscillator delivers a digital signal whose frequency is a measure of the voltage of the analog signal.
SUMMARY OF THE INVENTION
The present invention provides a trouble-free signal processing system for an air quality sensor.
In one embodiment of the device according to the present invention for measuring air quality, a sensor is provided whose sensor resistance is related to air quality. This sensor resistance is part of a signal processing system that converts the sensor resistance into an output signal with a period which is related to the sensor resistance. The period of the output signal is thus a measure of sensor resistance. This frequency-determined output signal is less sensitive to received interference or conductor-bound interference than would be an analog signal whose amplitude contains the useful information. Interference due to temperature effects can also be reduced. Time- and frequency-dependent output signals can be detected with a higher resolution than analog signals with some microcontrollers. If a binary signal with a variable period is available as the output signal, simple signal processing using digital technology is possible. This reduces the need for expensive analog components.
Voltage-time or voltage-frequency converters may be used for signal processing. These circuits, also known as voltage-controlled oscillators, are available as standard integrated circuits or chips.
In another embodiment according to present invention, an astable flipflop arrangement including an RC element and a comparator is used as the voltage-time converter. According to this embodiment, a capacitor is coupled between a reference potential and an inverting input of the comparator, and a first resistor is coupled to the output of the comparator. A sensor resistance is coupled between the reference potential and a non-inverting input of the comparator, and a second resistor is coupled to the output of the comparator. The output signal is picked off at the output of the comparator. This circuit design yields the result that the period of the output signal is a logarithmic function of the sensor resistance. The period of this logarithmic curve corresponds to the sensor resistance/air quality characteristics of the air quality sensors, which are also logarithmic or exponential. This yields a constant sensitivity over several decades. The need for analog log modules, which would also yield a constant sensitivity, is thus reduced. An output signal with a variable period is less susceptible to interference in comparison with the output signal of an analog log module.
The present invention also provides an air quality measuring device for use in motor vehicles. The ventilation systems are regulated as a function of the air quality.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a block diagram of a device for measuring air quality.
FIG. 2 illustrates a circuit arrangement of one embodiment of the device for measuring air quality.
FIG. 3a illustrates an output signal in accordance with an embodiment of the present invention.
FIG. 3b illustrates the output signal in accordance with another embodiment of the present invention.
DETAILED DESCRIPTION
An air quality 10 is converted by a sensor 11 into a test signal 12. Signal processing system 13 converts this test signal 12 into an output signal 14.
In one embodiment according to the present invention, signal processing system 13 includes a comparator 21, at whose non-inverting input a sensor resistor R.sub.s 17 is connected to a reference potential, and a second resistor R2 19 is connected to the output of comparator 21. A capacitor C 18 is connected to a reference potential at the inverting input of comparator 21, and a resistor R 20 is connected to the output of comparator 21. Output signal 14 is picked off against the referen
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Robert & Bosch GmbH
Wiggins J. David
Williams Hezron
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