JP2000329592A - Device for measuring physical quantity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a device for measuring physical quantity where measurement accuracy is improved while preventing the breakdown of an oxide layer being formed on the surface of a slide resistance plate and that of a slider and the generation of the oxide layer. SOLUTION: A sensor circuit 1 is in a three-terminal configuration with a power supply terminal where a pull-up resistor 3 and a sensor resistor 1c with a plurality of terminals are provided in series and one end of the pull-up resistor 3 is connected, a grounding terminal where one end of the sensor resistor 1c is connected, and a terminal for outputting a quantity to be measured where one end of a slider for switching the plurality of terminals of the sensor resistor 1c is connected. Also, a charge/discharge capacitor is connected between the terminal for outputting the quantity to be measured and the ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a physical quantity measuring circuit for measuring a physical quantity such as fuel.

[0002]

2. Description of the Related Art As a conventional physical quantity measuring circuit, for example, there is one as shown in FIG. This physical quantity measurement circuit is a circuit usually used in an electronic meter or the like, and measures and displays the amount of fuel. The configuration is such that a sensor circuit 101 that outputs a fuel amount in accordance with a change in resistance value is provided.
A switch circuit 104 connected between the sensor circuit 101 and the power supply terminal 102 via a pull-up resistor 103; and a meter for processing a measured quantity (hereinafter referred to as measurement data) from the sensor circuit 101. It includes a data processing circuit 105 such as an IC, and a driver circuit 106 that inputs data processed by the data processing circuit 105 and operates a display 107 such as a light emitting diode, for example.

As shown in FIG. 5, the sensor circuit 101 includes a conductor path array 101b for sliding a movable contact on an insulating substrate 101a such as a ceramic substrate and a resistance as a sensor resistance provided between the conductor paths. The body 101c is formed by a thick film technique or the like.

The data processing circuit 105 includes a switch circuit 1
04 and a first sampling pulse S1 for energizing the first and second sampling pulses S1 and S1.
And a sampling circuit 111 for outputting a second sampling pulse S2 falling earlier or at the same time as the sampling pulse S1, and sampling the measurement data supplied from the sensor circuit 101 with the second sampling pulse S2 for analog / digital conversion. (Hereinafter referred to as A / D) A / D conversion circuit 112 for conversion and this A / D conversion circuit 1
A decoding circuit 113 for decoding the digital data signal output from the decoder 12 into, for example, bar segment data;
A data transfer circuit 114 for transferring the decoded data signal to the driver circuit 106.

Next, the operation will be described. The switch circuit 104 is turned on / off by another first sampling pulse S1 outputted earlier than the second sampling pulse S2 outputted from the sampling circuit 111 to the A / D conversion circuit 112. That is, the first sampling pulse S1 rises earlier than the rising of the second sampling pulse S2, and is output so that the switch circuit 104 is turned on earlier than the A / D conversion circuit 112. This is because data is sampled after the voltage state of the sensor circuit 101 is stabilized.

The sensor circuit 101 includes a switch circuit 104
When the power is supplied through the slider 101d, the slider 101d is displaced in conjunction with the movement of a resin float (not shown) which moves up and down in accordance with the increase and decrease of the fuel, and is provided on the slider 101d. The contact 101e sequentially switches and connects the conductor paths 101b, so that the external connection terminals 101f of the sensor circuit 101 are connected.
And the resistance value between 101g changes. As a result, the measurement data accompanying the change in the resistance value is supplied from the external connection terminal 101f to the A / D conversion circuit 112 of the data processing circuit 105.

In the A / D conversion circuit 112, every time the second sampling pulse S2 is supplied, the sensor circuit 1
A / D conversion is performed on the measurement data supplied from 01, and the obtained digital data signal is output to the decoding circuit 113. The decoding circuit 113 converts the digital signal into, for example, bar segment data, and outputs it to the driver circuit 106 via the data transfer circuit 114. The driver circuit 106 causes the display 107 to display the measured value.

FIG. 6 is a flowchart showing the outline of the segment lighting process of the data processing circuit 105. In step S1, the A / D conversion circuit 112 captures the sensor output A. In step S2, the sensor output value is A ≦ F point (F point: F
(ULL) It is determined whether or not the display value is satisfied. If NO, the process proceeds to step 3 and the F point segment is turned on. If YES, proceed to step 4. In step 4, it is determined whether or not A ≦ F−1 point display value is satisfied. If NO, the process proceeds to step 5 and the F−1 point segment is turned on. If YES, the process proceeds to step 6, where the sensor output value is determined by comparing the Fn point segments as in steps S1 and S2. Such lighting determination operation is repeated, and finally, the lighting determination of the point E (empty) is performed.

At this time, the relationship between the "sensor resistance" and the "lighting threshold resistance value of the meter segment (value calculated backward from the A / D conversion circuit 112)" is as shown in FIG. I have. That is, the lighting threshold resistance value of the meter segment is set to be always between the adjacent sensor resistance values even if there is a variation error.

For example, in the case of FIG. 7 (b), when the sensor resistance value at the point F fluctuates on the max side and the lighting threshold resistance value of the meter segment fluctuates on the min side, sensor resistance value> meter segment The lighting threshold resistance value is reached, and the meter cannot light the point F segment.
If this occurs in the middle segment, a "display skip" that turns off the two segments at the same time occurs. Therefore, the segment lighting threshold resistance value of the meter is always set to be between the adjacent sensor resistance values, including the variation error of each component.

[0011]

Since the conventional physical quantity measuring device is constructed as described above, in order to improve the accuracy of the measuring device, when improving the sensor accuracy, that is, when improving the resolution of the sensor circuit, each of The lighting threshold resistance of the meter segment is set so that it does not overlap between sensor resistances, including variation errors, so if the resolution is to be improved, the number of contacts (resistance paths) will increase. However, there has been a problem that the sensor resistance value becomes high.

When the resistance value of the sensor increases, it becomes impossible to flow (reduce) a current that destroys an oxide film formed on the surface of the sliding resistor plate and the surface of the slider placed between the conductor plates. That is, an oxide film is formed on the surface of the sliding resistance plate and the surface of the slider by normal use, and this oxide film increases the contact resistance between the sliding resistance plate and the slider. Therefore, a certain amount of current is flowed between the contacts (between the resistance plates) (it fluctuates depending on the power supply voltage and the sensor position, but it is necessary to flow at least about several tens of mA) to prevent the formation of an oxide film. However, when the number of contacts is increased to improve the accuracy as described above, there is a problem that a current cannot flow and it is impossible to prevent the oxide film from being broken and the oxide film from being formed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has been developed in order to prevent the oxide film formed on the surface of the sliding resistance plate and the surface of the slider from being destroyed and to prevent the formation of the oxide film. An object is to obtain a physical quantity measuring device with improved accuracy.

[0014]

A physical quantity measuring apparatus according to the present invention comprises a sensor circuit for outputting a measured quantity in accordance with a change in resistance, a sampling circuit for outputting a sampling pulse, and a sampling circuit from the sampling circuit. An analog / digital conversion circuit that receives a pulse and converts an analog detection signal supplied from the sensor circuit into a digital signal, and a physical quantity measurement device that outputs an output of the analog / digital conversion circuit as a signal to be measured. A pull-up resistor and a sensor resistor having a plurality of terminals are provided in series, a power supply terminal connected to one end of the pull-up resistor, a ground terminal connected to one end of the sensor resistor, and a plurality of the sensor resistors. Terminal configuration having a measured output terminal to which one end of a slider for switching the terminal is connected. And, wherein is obtained by connecting a charging and discharging capacitor between ground and the measured amount of the output terminal.

[0015] The sampling circuit of the physical quantity measuring device according to the present invention is characterized in that the sampling circuit rises earlier than the rising of the second sampling pulse supplied to the analog / digital conversion circuit and continues until the falling of the second sampling pulse. A switch circuit is provided for outputting a sampling pulse and supplying power to the sensor circuit during a period when the first sampling pulse is being supplied.

In the physical quantity measuring device according to the present invention, a coefficient value obtained by using a power supply voltage supplied to the sensor circuit as a reference value is supplied to an analog / digital conversion circuit as a correction element of the measured value output from the sensor circuit. It has a measurement value correction circuit.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a block diagram showing a configuration of a physical quantity measuring device according to the first embodiment.
For example, a sensor circuit 1 that outputs a fuel amount corresponding to a change in resistance value, a switch circuit 4 that is connected via a pull-up resistor 3 between the sensor circuit 1 and a power supply terminal 2,
A data processing circuit 5 as a meter IC for processing the measurement data from the sensor circuit 1, a driver circuit 6 for inputting data processed by the data processing circuit 5 and operating a display 7 such as a light emitting diode, for example; It is provided with.

Since the sensor resistor 1c of the sensor circuit 1 can be adjusted by laser trimming or the like, it can be manufactured with relatively high accuracy. However, the conventional pull-up resistor 103 has a relatively large error because an existing metal oxide resistor is used.

Therefore, the pull-up resistor 3 is connected to the sensor circuit 1
The three-terminal sensor (power supply terminal 1)
e, measured quantity output terminal 1f and ground terminal 1g). However, if only the three-point configuration is used, no current flows through the contact portions (the slider and the sliding resistance plate), and the oxide film cannot be destroyed and removed.

This is because the data processing circuit 5 has a high input impedance, so that a current flows to the ground side of the sensor circuit 1. Therefore, a capacitor C is inserted between the slider 1d of the sensor circuit 1 and the ground E, and the sensor circuit 1
Power is supplied intermittently to charge and discharge the capacitor C in accordance with the intermittent driving of the power supply, and the current at the time of charging and discharging destroys the oxide film formed on the surface of the sliding resistance plate and the surface of the slider, and The purpose is to prevent formation of an oxide film.

The switch circuit 4 includes two switching transistors 4a and 4b. The data processing circuit 5 includes a first sampling pulse S1 for energizing the switch circuit 4 and a second sampling pulse S1 which rises later than the sampling pulse S1 and falls earlier or the same as the first sampling pulse S1.
2 and the measurement data supplied from the sensor circuit 1 are sampled by a second sampling pulse S2 to be analog / digital (hereinafter A).
/ D) A / D conversion circuit 12 for converting
A decoding circuit 13 for decoding a digital data signal output from the / D conversion circuit 12 into, for example, bar segment data, and a driver circuit 6 for decoding the decoded data signal.
And a data transfer circuit 14 for transferring the data to the memory.

Next, the operation of the switch circuit 4 will be described.
Is controlled on / off by another first sampling pulse S1 outputted earlier than the second sampling pulse S2 outputted from the sampling circuit 11 to the A / D conversion circuit 12. This first sampling pulse S1 rises earlier than the rising of the second sampling pulse S2, and A
The signal is output so that the switch circuit 4 is turned on earlier than the / D conversion circuit 12. This is because the measurement data is sampled after the measurement of the sensor circuit 1 is stabilized.

When the power supply voltage is supplied through the switch circuit 4, the sensor circuit 1 is provided on the slider 1d in conjunction with the movement of the resinous float that moves up and down in accordance with the increase and decrease of the fuel. When the contact sequentially switches and connects the conductor paths 1b, the resistance value generated at the measured output terminal 1f of the sensor circuit 1 changes. As a result, the measurement data accompanying the change in the resistance value from the measured output terminal 1f is supplied to the A / D conversion circuit 12 of the data processing circuit 5.

The A / D conversion circuit 12 A / D converts the measured data and outputs the obtained digital data to a decoding circuit 13. The decoding circuit 13 converts the digital signal into, for example, bar segment data and outputs it to the driver circuit 6 via the data transfer circuit 14, and the driver circuit 6
Causes the display 7 to display the measured value.

During the measurement operation of the sensor circuit 1, the capacitor C is charged and discharged, and the current flowing at this time destroys the oxide film formed on the surface of the sliding resistance plate and the surface of the slider and generates the oxide film. Can be prevented. If this current is to flow without charging / discharging the capacitor C, the input impedance Z of the sensor circuit 1 of the data processing circuit 5
Can not be higher. As shown in FIG. 3, the input impedance Z is in parallel with the sensor resistance Rs, and if the input impedance is reduced, the variation in the input impedance cannot be ignored. That is, if the input impedance is high, the parallel resistance Rs' with the sensor resistance Rs becomes R
s ′ = 1 / (1 / Z + 1 / Rs) ≒ Rs, and the input impedance Z can be ignored. If the input impedance Z cannot be neglected, a variation in the input impedance Z and a variation in the sensor resistance will be multiplied, and a large variation must be expected, so that an increase in accuracy cannot be expected.

As described above, according to the first embodiment, the sensor circuit 1 has the three-terminal structure including the pull-up resistor 3, and the capacitor C is connected between the measured output terminal for outputting the measurement data and the ground. Is connected, it is possible to prevent the oxide film formed on the surface of the sliding resistor plate and the surface of the slider from being destroyed and the oxide film from being formed by the charge / discharge current to the capacitor even if the input impedance Z is high. .

Embodiment 2 FIG. FIG. 2 is a timing waveform chart showing the relationship between the power supply voltage applied to the power supply terminal 1f, the current flowing through the capacitor C, and the voltage of the capacitor C.
This power supply voltage has an error, for example, 64 msec.
, And power is supplied for 8 msec, and the measured data is read when the capacitor voltage is stabilized. Therefore, the power is corrected by multiplying the measurement data from the sensor circuit 1 taken into the data processing circuit 5 by the coefficient obtained by the following equation. Coefficient = set reference voltage / value taken as sensor reference voltage

As described above, according to the second embodiment, the power is corrected by multiplying the measurement data from the sensor circuit 1 taken into the data processing circuit by the coefficient to correct the power supply. Measurement can be performed with high accuracy.

In the first and second embodiments, the power supply voltage is supplied to the sensor circuit only when the measurement operation is performed. However, if the sensor circuit consumes less power, the power supply is always supplied. You may. In the illustrated example, the fuel gauge has been described. However, the present invention can be applied to various measuring devices other than the above, such as a sliding resistance type pressure gauge, which measures a measured quantity by a change in resistance value.

[0030]

According to the present invention, a sensor circuit is provided with a pull-up resistor and a sensor resistor having a plurality of terminals in series, and a power supply terminal connected to one end of the pull-up resistor, A three-terminal configuration having a ground terminal connected to one end and a measured output terminal connected to one end of a slider for switching a plurality of terminals of the sensor resistor is provided between the measured output terminal and ground. Since the discharge capacitor is connected, the accuracy of the pull-up resistor can be improved, and even if the input impedance of the data processing circuit that inputs the measured amount from the sensor circuit is high, the charge / discharge current to the charge / discharge capacitor There is an effect that the oxide film formed on the surface of the sliding resistance plate and the surface of the slider can be prevented from being broken and the oxide film can be prevented from being formed. In addition to the destruction and prevention of the oxide film on the surface of the sliding resistance plate and the surface of the slider, the charge / discharge current of the charge / discharge capacitor causes the oxide film on the power supply terminal 1e, the output terminal under measurement 1f, and the ground terminal 1g to be formed. This has the effect of preventing destruction and formation of an oxide film.

According to the invention, the sensor circuit is supplied to the sensor circuit during the period in which the first sampling pulse which rises earlier than the rising of the second sampling pulse and lasts until the falling of the second sampling pulse is supplied. Since the power supply voltage is configured to be supplied, the power consumption is reduced, and the generation of an oxide film is reduced as compared with the case where the power is always supplied. There is an effect that it can be reduced.

Further, according to the present invention, since the measurement data output from the sensor circuit is corrected by the coefficient value obtained by using the power supply voltage as a reference value, even if an error occurs in the power supply voltage, the accuracy can be improved. There is an effect that measurement can be performed well.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a physical quantity measurement device according to a first embodiment of the present invention.

FIG. 2 shows a sensor power supply and a capacitor C in the apparatus shown in FIG.
FIG. 4 is a timing waveform chart showing a relationship between a current flowing through a capacitor C and a voltage of a capacitor C.

FIG. 3 is an equivalent circuit diagram showing a relationship between a sensor resistance and an input impedance.

FIG. 4 is a block diagram showing a configuration of a conventional physical quantity measuring device.

FIG. 5 is an enlarged plan view of a main part of the sliding resistance plate.

FIG. 6 is an explanatory diagram in which a variation range of a sensor resistance value and a variation range of a segment lighting threshold value of a display are not overlapped.

FIG. 7 is an explanatory diagram in which a variation range of a sensor resistance value and a variation range of a segment lighting threshold value of a display are wrapped.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sensor circuit 1c Sensor resistance 3 Pull-up resistance 4 Switch circuit 11 Sampling circuit 12 A / D conversion circuit S1 First sampling pulse S2 Second sampling pulse

Claims (3)

[Claims] 1. A sensor circuit for outputting a measured quantity in accordance with a change in resistance value, a sampling circuit for outputting a sampling pulse, and an analog detection circuit which receives a sampling pulse from the sampling circuit and is supplied from the sensor circuit. An analog / digital conversion circuit for converting a signal into a digital signal, and a physical quantity measuring device for outputting an output of the analog / digital conversion circuit as a signal to be measured, wherein the sensor circuit includes a pull-up resistor and a sensor resistor having a plurality of terminals. Are provided in series, and a power supply terminal to which one end of the pull-up resistor is connected, a ground terminal to which one end of the sensor resistor is connected, and a terminal to which one end of a slider for switching a plurality of terminals of the sensor resistor are connected. A three-terminal configuration having a measured quantity output terminal, and a charge / discharge capacitor between the measured quantity output terminal and ground A physical quantity measurement device characterized by connecting a sensor. 2. A sampling circuit outputs a first sampling pulse which rises earlier than a rising of a second sampling pulse supplied to an analog / digital conversion circuit and lasts until the falling of the second sampling pulse. 2. The physical quantity measuring device according to claim 1, further comprising a switch circuit for supplying power to the sensor circuit during a period in which the first sampling pulse is supplied. 3. A measurement value correction circuit for supplying a coefficient value obtained by using a power supply voltage supplied to a sensor circuit as a reference value to an analog / digital conversion circuit as a correction element of a measurement value output from the sensor circuit. The physical quantity measuring device according to claim 1 or 2, wherein: