GB2277596A - Gauge with a moving indicator and adjustable sensitivity - Google Patents

Description

2277596

-1DESCRIPTION

GAUGE WITH A MOVING INDICATOR AND ADJUSTABLE SENSITIVITY The present invention concerns a gauge with a moving indicator and adjustable sensitivity, in which a memory means is provided for determining the sensitivity of an amplification system arranged for controlling the deflection of the indicator as a function of a signal representing a quantity to be displayed.

The term "indicator,, is intended to mean a component whose deflection or position, amongst a plurality of positions, is a function of the value of the quantity to be displayed. and indicators of the type with pivoting flaps bearing characters and which can occupy one of two predetermined functional positions, are excluded from the scope of the present application.

A gauge with a moving indicator is used for example in a vehicle revolution counter, in order to display the speed of rotation of the engine. It includes a drive movement serving to deflect the indicator as a function of a control signal, the value of which is thus displayed by the deflection of the indicator.

As it is a case of effecting a relative movement between an indicator component and a scale of values, the indicator may be a rotary disc bearing, at its periphery, the scale of values passing through a fixed reading window.

Usually it is a case of a needle moving, in rotation or translation, in front of a dial bearing a scale of values which may incorporate a red overspeeding sector, in the case of a car engine.

Depending on the type of car, the corresponding limit varies, since the engine of a sports car may achieve, without any damage, a higher speed than the engine of an ordinary car. However. as the intended deflection range of the gauge of an ordinary car is already relatively high, this range cannot be extended to use this same gauge in a sports car. A gauge of another type would therefore be needed for the latter and the production runs would be smaller and therefore more expensive.

In reality, a single type of gauge is indeed used but, for sports cars, the sensitivity of the gauge is adjusted by decreasing it so that the size of the deflection range remains unchanged, the scale of the speeds of rotation of the engine being corrected accordingly.

The drive mechanism for the indicator must be controlled by control electronics which are individualised, that is to say in which is memorised the sensitivity which the amplification system for the signal to be displayed must have, the said signal coming, in the example in question, from a rotation speed sensor.

Gauges are already known in which a numerical value defining this sensitivity is stored in an EEPROM memory (electrical erasable memory) associated with a microcontroller which adjusts, as a function of this sensitivity. the gain or sensitivity of an amplifier controlling the mechanism driving the indicator.

However, the use of an EEPROM memory is not easy. In addition, its cost is not insignificant.

Gauges are also known in which the sensitivity is defined not by an EEPROM memory but by logic levels applied to an input port of the microcontroller. However, unless a very large number of them are provided and the complexity and cost are consequently increased, these logic levels allow only a limited choice of discreet values. In addition, the input port is limited by the format of the data processed by the microcontroller. Moreover. the links supplying these logic levels are, after the development of a prototype, integrated into the microcontroller production mask, so that an error is very expensive -4and a modification, even slight, of the sensitivity, in order, for example, to modify the style of the gauge, is not very realistic economically.

The present invention aims to propose a satisfactory solution.

To this end, it provides a gauge with a moving indicator of the type mentioned above, in which the memory means include a divider network, the division ratio of which determines the said sensitivity.

In this way the value of the division ratio can easily be selected, for example by an appropriate choice of the impedance of one or more electronic components or by the adjustment of factory-fitted components.

Advantageously, computing means are provided, arranged for receiving a signal representing the division ratio of the divider network in order to eliminate therefrom, by division by a predetermined factor, least significant figures deemed to be uncertain, and for multiplying the result of the division by a predetermined number representing a step in the adjustment of the sensitivity of the amplification system. The sensitivity model is advantageously linear.

It is thus possible to get rid of the uncertainty related, for example, to the degree of accuracy of the -5divider network and to use components which are of relatively low accuracy and therefore inexpensive. The number representing the division ratio is thus, as it were, rounded to the closest value which is deemed to be exact and the sensitivity of the amplification system then has the exact value desired.

Advantageously again, the divider network is a resistance bridge.

These are therefore inexpensive components, with a value which may be very precise and very stable, in particular with regard to temperature and relative humidity, and fairly insensitive to perturbations.

In particular, if the divider network includes a ladder of switchable resistors, these resistors may systematically be fitted in the factory. Thus there is only a single type of gauge, which is then adapted by connecting the desired resistors, for example by means of jumper links in series with each of them, if they are mounted in parallel with each other, or jumper links short-circuiting them if they are all in series.

Still advantageously, the resistors are adjustable.

It is thus possible, in an automatic system, to carry out a dynamic adjustment of the sensitivity by injecting a given signal at the input to the -6amplification system and by adjusting a resistor until the deflection which the indicator is intended to have is obtained.

The invention will be understood better by means of the following description of a preferred embodiment of a moving-indicator gauge in accordance with the present invention, given with reference to the single accompanying figure which is a representation thereof in functional blocks.

The gauge shown belongs, in this example, to a vehicle revolution counter. It includes a control circuit 1 controlling a movement 2 driving, in this case, a needle 3, rotary in this example.

The control circuit 1 includes a microcontroller 11 connected at its input to an input terminal 4 of the control circuit 1 receiving a tachometric signal with a frequency proportional to the speed of rotation of the vehicle engine. The microcontroller 11 is connected, by means of an output 5. to the input of an amplifier 6, itself connected at its output to a movement control input 2 through an output terminal 7 of the control circuit 1.

The microcontroller 11 includes an analogue to digital converter 12 receiving, at a reference input, a reference voltage Vref also applied to one end of a divider network formed in this case by two resistors 8 1 -7and 9, the intermediate point of which, at a voltage Ve, is connected to a measuring input of the analogue to digital converter 12 and the opposite end of which is earthed.

The output of the analogue to digital converter 12 is connected to a computing unit 13 of the microcontroller 11, including an arithmetic unit 14 and a program memory 15.

A programmable-gain amplifier 16 of the microcontroller 11 connects the input terminal 4 to the output terminal 5, through the computing unit 13 transforming the tachometric signal into a voltage. The gain of the amplifier 16 is controlled by a digital signal 17 coming from the computing unit 13.

The functioning of the control circuit will now be explained.

The tachometric signal applied to the terminal 4 controls the movement 2 through the programmable-gain amplifier 16 and the amplifier 6, the latter having here only the role of a fixed-gain power amplifier.

The gain, or sensitivity, of the amplifier 16 is adjusted as follows.

The analogue to digital converter 12 uses the voltage Vref as a reference voltage for its input stage (not shown). The voltage Ve is thus compared with the voltage Vref and the analogue to digital -8converter 12 supplies, to the computing unit 13, a number n increasing from 0 to nMAX = 2N _ 1, where N is a positive integer equal to the number of bits of the analogue to digital converter 12, when the ratio Ve/Vref varies from 0 to 1. In this example N equals 8.

For the sake of clarity of the disclosure, the gain of the amplifier 16 is assumed to increase linearly with the value of the digital signal 17. A circuit (not shown). at the input to the amplifier 16, converts the signal 17 into a corresponding control voltage.

The memory 15 contains a numberp corresponding to the adjustment step of the signal 17. that is to say 1/(2N _ 1) times the maximum value of the signal 17, and a function of the sensitivity of the gain of the amplifier 16 with respect to the signal 17.

The computing unit 13 reads the number p in the memory 15 and multiplies it, by means of the arithmetic unit 14, by the number n coming from the analogue to digital converter 12, which supplies the signal 17 in the form of a number equal to n x p and fixes the gain G of the amplifier 16, with respect to its maximum value GM, at a ratio n nMAX G1M Ve Vrdf It will be understood that an analogue control sequence starting from the signal Ve in order to provide an analogue signal 17 would be just as suitable, since it would have sufficient accuracy.

In this example, the resistors 8 and 9 have an accuracy of 1% and, with the electrical noise and the accuracy of the analogue to digital converter 12 it is considered that only the six most significant bits are exact out of the N = 8 bits.

In order to avoid taking the above "noise" or uncertainty into account. the computing unit 13 is programmed to reject a number n of 8 bits in which the two least significant bits do not represent a given number amongst the four possible combinations for these two least significant bits.

In other words, amongst the 2N = 256 possible numbers n, a quantified scale of 64 equally distributed exact numbers is defined, separated from each other by 4 units, and the computing unit 13 calculates a rounded value of the measured number n by choosing the quantified number n which is the closest to the measured number n. which thus eliminates any error in the computing of the signal 17.

The error on the measured number n may be manifested negatively and, as a result of the carry being blocked in the analogue to digital converter, -10which propagates from the least significant to the most significant, this error could falsify the value of the six most significant bits.

In order to avoid such an error in relation to the most significant bits, the computing unit 13 adds first of all, to the measured number n, the highest least significant bit of the two, that is to say 2 units. This has the effect of positively shifting the uncertainty range, initially centred on the exact value of n ( 2 units), by a value substantially equal to half this range, the latter thus being with certainty moved into the area + 0 to + 4 units above the exact value n.

It then suffices to force the two least significant bits to zero in order to obtain the estimated quantified value.

Applied in the decimal system, the correction of a measured number n equal to 98 with a range of uncertainty of 5, that is to say a quantification step of 10, whilst the theoretical value of n is 100, would result in calculating 98 + 5 = 103 and eliminating the figure 3 from the units in order to obtain an estimated value n: 100.

It will be noted that, on the other hand, provision could be made to select the value of the resistors 8 and 9 so that they would supply a number n -11a little higher than the desired quantified number, so that the position of the range of uncertainty would thus be systematically biased and shifted positively so as to be accurate above the quantified number n. That would then make it possible to determine the quantified number n simply by truncation of the measured number n, without effecting the prior addition, indicated above, of the two least significant units.

In this example, the forcing to zero of the two least significant bits in fact takes place by truncation, by causing the positions of these two bits to disappear, that is to say by shifting to the right the 6 most significant figures by a quantity D = 2 positions. The measured number n is thus divided by a factor 2D = 4. To compensate for the effect of this division, the number R representing the amplitude of the voltage corresponding to the adjustment step of the signal 17 was previously multiplied by 2D - 4. The forcing to zero, mentioned previously, of the two least significant bits is equivalent to dividing by 2D 4 followed by multiplying by 2D = 4.

As the above uncertainty may be variable, and may be determined by the microcontroller 11, for example as a function of the number n or of the accuracy, indicated by the user, of the resistors 8 and 9, -12provision could be made to effect a truncation on a given but variable number of least significant bits, a number increasing with this uncertainty. In this case, if a corresponding shifting towards the right were again effected. the corresponding number R would have a fixed value, without any previous multiplication, and the number n would then be multiplied, that is to say shifted towards the left by as many positions as it has been shifted towards the right.

In general terms, the gain G is of the form:

G = (2 D x p) X n + B 2 D B being a constant, stored in the memory 15, which is if necessary added, in the arithmetic unit 14, to the signal 17 in order to shift the position of rest of the needle 3.

It will be noted that the above operations are facilitated if D is an integer as in this example, but that this condition is not essential.

It is possible to produce the resistors 8 and 9 in the form of a single potentiometer on which the slide supplies the voltage Ve. It is also possible to provide, for each resistor 8-9 a ladder of resistors in parallel or series which are brought into service individually in order to adjust the equivalent resistor, by fitting jumpers respectively in series and in parallel with their associated resistors.

Likewise, adjustable resistors can be provided, such as attached pads, screen-printed resistors or resistive ink, which may be adjusted by a machine for the dynamic adjustment of the gain of the gauge.

Another possibility is to use other types of components in place of at least one of the resistors 8 and 9, for example a capacitor or inductor, and to provide a voltage Vref which is alternating. Where the components, or set of components, 8 and 9 have impedances of different natures, modification of the frequency of the signal Vref would make it possible to fix the attenuation ratio Ve/Vref without modifying the components 8-9.

It will be understood that the invention may also be applied to a gauge with a moving indicator other than the needle 3, for example a gauge with a needle or any other pointer which is movable with respect to rotation, translation or otherwise. Likewise, this could be dial, bearing a scale of values, which moves with respect to a marker.

Claims (1)

1. A gauge with a moving indicator and adjustable sensitivity, in which a memory means is provided for determining the sensitivity of an amplification system arranged for controlling the deflection of the indicator as a function of a signal representing a quantity to be displayed, the memory means including a divider network whose division ratio determines the said sensitivity.

2. A gauge according to Claim 1, including a computing means which is arranged to receive a signal representing the division ratio (n) of the divider network, and to eliminate therefrom, by division by a predetermined factor, least significant figures considered to be uncertain, and to multiply the result of the division by a predetermined number (p) representing a step in the adjustment of the sensitivity of the amplification system.

3. A gauge according to Claim 1 or 2, in which the divider network is a resistance bridge.

4. A gauge according to Claim 3, in which the divider network includes a scale of switchable resistors.

S. A gauge according to Claim 3 or 4, in which the resistors are adjustable.

n -is- 6. A gauge according to Claim 4, in which the divider network includes a potentiometer.

7. A gauge substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

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