The present invention is directed to a device for evaluating the signal from a viscosity sensor.
In previously proposed devices, the signal from the viscosity sensor is amplified.
The device according to the present invention for evaluating the signal from a viscosity sensor, in contrast to the related art, has the advantage that partial compensation is made for the strong influence of temperature on the measurement variable viscosity. It is thus possible to greatly reduce the wide divergence in the range of values of the measurement signal caused by the influence of temperature on the viscosity, thereby permitting higher resolution in the evaluation of the measurement signal.
The use of an amplifier which an input for the signal from the viscosity sensor and an additional input for a signal from the temperature sensor is particularly simple. Amplification of the amplifier is controlled by the signal from a temperature sensor. It is advantageous if the viscosity sensor and the temperature sensor are situated in immediate proximity to one another in the measurement liquid; this ensures that the measurement values from the viscosity sensor and the temperature sensor are based on the same temperature. The design of the viscosity sensor as a microacoustic sensor is particularly simple.
The device described in
A microacoustic sensor, for example, is used for the measurement of viscosity. In such microacoustic sensors an oscillating element is inserted into the oil, and the oscillation frequency of the oil or the damping of this oscillation is a measure of the viscosity. In the following description it is assumed that the oscillation frequency or damping is converted to an analog signal which represents the viscosity. (The frequency may be converted using a frequency-voltage transformer, for example.)
In such microacoustic sensors, a sensor signal VS from the viscosity sensor is proportional to density ρ or to viscosity η, according to formula 1:
VS∝(ρη)1/2 (1)
or alternatively, is proportional to a corresponding reciprocal value:
VS∝1/(ρη)1/2 (2)
A typical sensor for engine oil has, for example, a sensor characteristic for viscosity as expressed by formula 2. In conjunction with dependence of the oil viscosity on temperature, this results in an approximately linear course of the viscosity signal VS from the sensor as a function of the temperature, according to the following formula:
VS≈k1+k2T (3)
Constants k1 and k2 are constants which depend on the grade of oil. The dependence of the oil viscosity on temperature may thus be characterized by two constants. Sensor signal VS is fed into amplifier 2 and is amplified with amplification A:
V=A·VS (4)
According to the present invention, amplification A is provided with a temperature dependence so that emitted signal V is influenced by temperature as little as possible over the intended temperature range, and thus always represents a direct measure of the oil viscosity. For the dependence of viscosity on the temperature as represented in formula 3, an amplification is provided in the following form:
A≈1/(c1+c2T) (5)
Parameters C1 and C2 are again constants. Naturally, the constants are most favorably selected such that K1=C1 and K2=C2. This makes it possible for output signal V to be a fully temperature-dependent measure of the oil viscosity which is characterized by constants K1 and K2. Usually, constants C1 and C2 may be selected so that the parameters are very similar for the numerous engine oils, so that the temperature dependence of the viscosity measurement of engine oils may be significantly decreased. In this way, it is possible to prevent a wide divergence in the value range of V caused by the strong dependence of the oil viscosity on temperature. Consequently, subsequent digital processing results in significantly higher resolution in the viscosity measurement.
Number | Date | Country | Kind |
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101 31 429 | Jun 2001 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/DE02/01708 | 5/11/2002 | WO | 00 | 10/8/2003 |
Publishing Document | Publishing Date | Country | Kind |
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WO03/004999 | 1/16/2003 | WO | A |
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0 884 578 | Dec 1998 | EP |
Number | Date | Country | |
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20040045344 A1 | Mar 2004 | US |