GB2361066A

GB2361066A - Oil level indicator with signal processor

Info

Publication number: GB2361066A
Application number: GB0030487A
Authority: GB
Inventors: Stephen Curtolo
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-12-17
Filing date: 2000-12-14
Publication date: 2001-10-10
Anticipated expiration: 2020-12-14
Also published as: DE10058008A1; GB0030487D0; DE10058008B4; GB2361066B

Abstract

A device for the purpose of obtaining a desired signal. A desired signal-generator (14) generates at least one desired signal (N) from at least one input signal (E). A reference signal-generator (10, 16, 18, 22, 24) generates at least one reference signal (R). The reference signal-generator (10, 16, 18, 22, 24) generates the reference signal (R) in dependence upon the input signal (E).

Description

2361066

1 DESCRIPTION

DEVICE FOR THE PURPOSE OF OBTAINING A DESIRED SIGNAL The invention relates to a device for the purpose of obtaining a desired signal of the type having a desired signal-generator which generates at least one desired signal from at least one input signal, which is output by a sensor, and from at least one reference signal, having a reference signal-generator which generates at least one reference signal.

DE 196 35 162 AI discloses a measuring device which comprises a measured value evaluating device, sensor means for the purpose of detecting an interference variable and a signal preprocessing device. Via an analog sensor output, the sensor means output sensor signals which are transmitted via the signal preprocessing device to the measured value evaluating device. In so doing, a differential signal is formed in the signal preprocessing device from the sensor signals and the reference signal and is transmitted to the measured value evaluating device for evaluation purposes. By suitably selecting the reference signal, it is possible to form various measurement ranges whilst retaining effective measurement resolution in each case. The measurement range can be changed over in dependence upon the output signal of the signal preprocessing device.

It is an object of the present invention to improve the detection of the desired 1 1 j 7) 2 signal for various starting conditions.

In accordance with the present invention, there is provided a device for the purpose of obtaining a desired signal, having a desired signalgenerator which generates at least one desired signal from at least one input signal, which is output by a sensor, and from at least one reference signal, having a reference signalgenerator which generates at least one reference signal, the reference signalgenerator generating the reference signal in dependence upon a step response of the input signal.

Taking into consideration the step response of the input signal during formation of the reference signal serves to increase the accuracy of generating the desired signal. In particular, in the case of sensor signals which fluctuate to a considerable extent, as is the case for example in oil level sensors., it is possible in this manner to determine the desired signal precisely, so that the resolution can be increased during detection of this desired signal.

In one expedient development, it is provided that the reference signalgenerator stores the input signal for the purpose of generating the reference value. For example, so-called sample-and-hold-members can be used as the reference signalgenerator. The stored continuous component of the input signal can be used as the reference signal which is taken into consideration for the purpose of generating 1 1C 1 4) 3 the desired signal. For example, an operational amplifier can be used as the desired signal-generator. The reference signal is transmitted to the operational amplifier at its inverting input. The desired signal is sensed at the output of the operational amplifier. In the case of different operating states, the associated reference value is newly formed on each occasion by virtue of the corresponding storage of the input signal. As a consequence, the reference value can be adapted in a flexible manner to suit various operating states. lle desired signal is provided with a high degree of reliability by updating the reference value which represents the interference variable.

In one expedient development, a microprocessor is provided as the reference signal-generator. In general, it is possible to fall back upon an already existing microprocessor which controls, for example, a sensor which provides the input signal. Since the microprocessor is already provided for specific functions, additional means, such as e.g. Zenerdiodes, are no longer required for the purpose of generating the reference signal. This serves to reduce production costs.

In one expedient development, the analog input signal can be converted to a digital signal in the microprocessor. In dependence upon the input signal, the microprocessor provides a pulse width-modulated output signalThe A/D conversion enables the microprocessor to determine a corresponding reference value. At the same time, the reference signal determined in the microprocessor 1 ';r J 4 can be converted to an analog reference signal by the pulse width in conjunction with a smoothing device.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:- Figures 1 and 2 show a block diagram in each case, Figure 3 shows the progression with respect to time of three signals of a first exemplified embodiment, Figure 4 shows a flow-diagram of a control program of the exemplified embodiment, and Figure 5 shows the progression with respect to time of four signals in the case of an alternative exemplified embodiment.

A microprocessor 10 generates a control signal S which is used for the purpose of controlling a current source 12. The current source 12 supplies a sensor 13 with current. The sensor 13 is a temperature- dependent resistor. The voltage drop at the sensor 13 serves as an input signal E for the microprocessor 10. Moreover, the 1 v 1 input signal E is transmitted to an operational amplifier which in conjunction with a feedback resistor 15 has been connected to a difference amplifier 14. The microprocessor 10 generates an output signal A from the input signal E. A reference signal R is formed from the output signal A of the microprocessor 10 which is smoothed. A capacitor 16 which is connected to earth, and a resistor 18, to which the output signal A of the microprocessor 10 is transmitted, are provided for the purpose of carrying out the smoothing operation. The output signal of this lowpass filter is transmitted as a reference signal R to the non-inverting input of the difference amplifier 14. The difference signal which is formed from the input signal E and the reference signal R is amplified by virtue of the difference amplifier 14 and transmitted to the microprocessor 10 as a desired signal N. The microprocessor 10 controls a display 20.

The exemplified embodiment as shown in Figure 2 differs from that shown in Figure 1 in that the microprocessor 10 controls a switching means 22. When the switching means 22 is in the closed state, the input signal E passes to a memory capacitor 24 which is connected to earth. The potential applied jointly to the switching means 22 and the memory capacitor 24 is transmitted to the noninverting input of the difference amplifier 14.

In the case of the exemplified embodiment as shown in Figure 1, the reference signal-generator consists of the microprocessor 10 having a memory, and of the 1 6 smoothing device which is formed from the capacitor 16 and the resistor 18. In the case of the exemplified embodiment as shown in Figure 2, the reference signal-generator consists of the microprocessor 10, the switching means 22 and the memory capacitor 24.

The circuit arrangements as shown in Figures 1 and 2 are used for the straightforward offset compensation of the input signal E which is provided by the sensor 13. An example of the signal progression of the input signal E is illustrated in Figure 3. The microprocessor 10 together with the control signal S activates the current source 12. The sensor 13 reacts, in dependence upon the ambient temperature, with a step response which, for example, assumes the illustrated progression. The first step response 30 of the input signal E (reference numeral 30) comprises a higher continuous component and in this application of an oil level status sensor corresponds to the situation that the oil is relatively warin. However, in the case of cold oil, reference numeral 32, the input signal E of the sensor 13 comprises a lower continuous component. The arrangements as shown in Figures 1 and 2 should also reliably eliminate the interference signal for various operating states (warm and cold oil). The interference signal is the continuous component of the input signal E. This continuous component is transmitted as a reference signal R to the non-inverting input of the difference amplifier 14. As a consequence, the difference amplifier 14 amplifies only the alternating component of the input signal E. The desired signal N which is detected by the 11 4 7 microprocessor 10 for the purpose of evaluating the sensor signal is applied to the output of the difference amplifier 14. After filtering out the offset component, it is possible to increase the amplification factor of the operational amplifier which is connected as a difference amplifier 14. The desired signal N which is produced as a result is detected in an optimum manner by the microprocessor 10.

The determination of the reference signal R will be described hereinunder. The microprocessor 10 controls the sensor 13 via the activation of the current source 12 with the aid of the control signal S. Moreover, the microprocessor 10 performs the interference variable compensation by controlled specification of the reference signal R. If the input signal E (sensor output signal) is to be detected for the purpose of determining the reference value, then the microprocessor 10 controls the current source 12 by activating it, cf. Figure 3. The microprocessor 10 is aware of the point in time at which the current source 12 is activated. After time period T I, calculated from the point in time at which the current source 12 is activated, the microprocessor 10 detects the first measured value M 1 of the input signal E. For this purpose, it is necessary to provide, for example, an AID conversion. The time period Tl is to be selected such that the continuous component of the input signal E, the interference variable, is determined and the transient effect of the system is concluded at the same time. For example, the time period T 1 is of the order of 10 ms. The microprocessor 10 stores the first measured value M F, which is detected after time period T I and is derived from

8 M I, and as the output signal A outputs a variable which is proportional to the detected measured value M I. The derived measured value M F can either be calculated from the input signal E or measured as a desired signal N. The output signal A is a pulse width-modulated signal, whose pulse width is dependent upon the detected measured value M 1. The smoothing member, which consists of the capacitor 16 and the resistor 18, forms the analog reference signal R from the binary output signal A. The reference signal R which is proportional to the measured value M I corresponds to the continuous component of the input signal E after time period T I. This reference signal R is transmitted to the inverting input of the difference amplifier 14. The desired signal N which is applied to the output of the difference amplifier 14 was compensated by the continuous component (corresponds to the reference signal R).

The exemplified embodiment as shown in Figure 2 differs in the way the reference signal R is determined and provided. As the current source 12 is activated, the microprocessor 10 controls the switching means 22 by closing it. Therefore, the memory capacitor 24 is charged to the level of the continuous component. After time period T I, the switching means 22 is then opened immediately, so that only the continuous component of the input signal E passes as the reference signal R to the inverted input of the difference amplifier 14.

The control program which is stored in the microprocessor 10 is illustrated in a 9 simplified manner in Figure 4. After the start, step 101, the microprocessor 10 activates the current source 12, step 103. Beginning with the output of the corresponding control signal S, the microprocessor waits for the time period Tl to pass (e.g. 10 ms), step 105. Only then is step 107 reached, in which the current first measured value M I is determined. This is followed by a plausibility test during the interrogation 109. The input signal E having the associated measured value M1 or the first derived measured value Ml'should range within predetermined limits, for example between 1.6 and 4.5 V. If the first measured value M 1 is less than 1. 6 V, then step 113 is reached. If the first measured value M 1 is greater than 4.5 V, then step 111 follows. Both steps 111, 113 are followed by an error diagnosis step 115. If the first measured value M 1 is within the permissible limits, then the microprocessor 10 generates a pulse width-modulated output signal A which corresponds to the first measured signal M 1, step 117. The difference amplifier 14 is influenced by the smoothed output signal A which corresponds to the reference signal R. A first comparative value Wwhich is stored for subsequent calculations is now applied to the output of the operational amplifier. In a subsequent step 119, the microprocessor 10 allows a second time period T2 of e.g. 875 ms to pass. This guarantees that the systems achieves a meaningful second measured value N2. The desired signal N is now detected, which serves to produce the second measured value M2, step 121. This is followed by another plausibility test in step 123. If the second measured value M2 is outside a permissible range, for example between 1.3 and 4.5 V, then step 129 follows. Otherwise, the change in the desired signal N to the second measured value M2 is detected by the microprocessor 10, step 125. Subsequently, the initial value MVis deducted from this value N2 and the oil level status is calculated. The resolution of the A/D conversion of the detected physical wanted signal N is thus improved according to the amplification factor of the operational amplifier which can be set higher. The configuration of the operational amplifier has been designed accordingly.

The device is preferably used for the purpose of evaluating sensor signals, of which the interference component fluctuates to a considerable extent, such as e.g. when determining the oil level status. However, the application is not limited thereto.

In an alternative mode of operation to Figure 1, similar results are obtained, only the microprocessor 10 is used in a closed control circuit structure. The corresponding signal progressions which are described hereinunder are illustrated in Figure 5. In order to detennine the measured value, the current source 12 is activated for a predetermined time period, as shown by the progression of the control signal S. The microprocessor 1 c detects the input signal E at time T 1 and calculates the first comparative value PWM-Anf which is stored. In order to determine the measured value, the microprocessor 10 generates periodically (Ln) a corresponding PWM-output signal A which after smoothing is transmitted as the 11 reference signal R to the non-inverting input of the difference amplifier 14.

if the input signal increases as a result of the oil being heated (cf. Figure 5), this increase is used for the purpose of resetting the PWMsignal A in such a manner that on the whole the desired signal N is kept constant. After a defined time period T2, the PWM-signal A is detected once again and this produces the second comparative value PWM-End. The oil level is detern-iined by the calculation PWM-End - PWM-Anf and is proportional to this difference.

12

Claims

1. A device for obtaining a desired signal, having a desired signalgenerator which generates at least one desired signal from at least one input signal, which is output by a sensor, and from at least one reference signal, having a reference signal-generator which generates at least one reference signal, the reference signal-generator generating the reference signal in dependence upon a step response of the input signal.

2. A device according to claim 1, wherein in order to generate the reference signal, switching means are provided for the purpose of storing the input signal.

3. A device according to any of the preceding claims, wherein the reference signal-generator controls the input signal.

4. A device according to any of the preceding claims, wherein the reference signal-generator influences the sensor with a step signal which has a predeterminable duration.

A device according to any of the preceding claims, wherein a microprocessor is used as the reference signal-generator.

13 6. A device according to claim 5, wherein a pulse width-modulated signal is used as the output signal.

7. A device according to claim 5 or 6, wherein the output signal is transmitted to a smoothing device which generates the reference signal.

8. A device according to any of the preceding claims, wherein the storage means is provided in the form of a memory capacitor which serves to gene rate the reference signal.

9. A device according to any of the preceding claims, wherein a microprocessor controls a switching means, in order to activate the storage means.

10. A device according to any of the preceding claims, wherein an operational amplifier, preferably a difference amplifier, is used as the desired signal-generator.

11. A device according to claim 10, wherein the operational amplifier is a difference amplifier.

12. A device according to claim 10 or 11, wherein the reference signal is transmitted to the operational amplifier.

14 13. A device for obtaining a desired signal, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.