JP2005249711A - Measuring circuit for internal resistance of sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring circuit for internal resistance of sensor which can measure with high precision, in addition to expand the measuring range of the internal resistance. <P>SOLUTION: The measuring circuit for internal resistance of sensor has a configuration, such that a measuring bias supply VCC impresses reverse bias to a sensor 10, and based on the output voltage of the sensor 10 measured with an amplifier AMP 1 and the voltage drop of measuring resistive group RV measured with an amplifier AMP 2, a microcomputer 11 implements variable control for the resistance of the measuring a resistive group RV so that it is equal to the resistance of the internal resistance RS of the sensor 10 to the resistance of the measuring resistive group RV, connected in series with the internal resistance RS of the sensor 10 resulting in the internal resistance RS of the sensor 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sensor internal resistance measurement circuit that improves the measurement range of the internal resistance of a sensor.

  Conventionally, as a technique for measuring the internal resistance of a sensor, for example, those described in the following documents are known (see Patent Document 1). The sensor internal resistance measuring circuit described in this document is shown in FIG. In FIG. 2, the sensor 20 to be measured includes an internal resistance RS and a sensor output power supply VS that outputs a sensor voltage VS. In this sensor 20, when the internal resistance RS is measured, a voltage VG (for example, about 5V) is supplied to the sensor output power supply VS via a switch SW and a series resistance RV connected in series between the bias power supply VG and the sensor 20. On the other hand, it is applied with a reverse bias. The voltage VM between both ends of the sensor 20 is input to the amplifier 21 and measured, and the output of the amplifier 21 is supplied to the A / D conversion port A / D of the microcomputer (μC) 22 for obtaining the internal resistance RS based on this output. Given.

  In the sensor internal resistance measurement circuit configured as described above, when the switch SW is turned on and the voltage VG is applied to the sensor 20, a current I flows through the sensor 20. Thereby, the voltage VM between the terminals of the sensor 20 is expressed by (Equation 1).

(Equation 1)
VM = I × RS + VS
The voltage VG is expressed by (Equation 2).

(Equation 2)
VG = I × RV + VM = I × RV + I × RS + VS
From the above, the internal resistance RS of the sensor 20 is expressed by (Equation 3).

(Equation 3)
RS = RV (VM-VS) / (VG-VM)
Here, RV and VG are preset and known values, VM is measured by the amplifier 21 when the switch SW is turned on (when measuring the internal resistance), and VS is measured when the switch SW is turned off (normality of the sensor 20). Measured by amplifier 21 during operation). Therefore, the internal resistance RS of the sensor 20 is calculated based on these measurement results and the above (Equation 3).

In such a sensor internal resistance measurement circuit, the internal resistance RS of the sensor 20 preferably has a measurement range of about 10Ω to about 1MΩ in consideration of the ambient conditions of the sensor and self-heating due to the operating current. Also, the series resistance RV should not be very different from the resistance value of the internal resistance RS. Therefore, if the measurement range of 10Ω (sensor temperature is about 900 ° C.) to 1 MΩ (sensor temperature is about 250 ° C.) described above is to be covered, the series resistance RV is, for example, about 68Ω, about 3.3 kΩ, and about 150 kΩ. Two resistors are required.
Japanese National Patent Publication No. 04-501170

  As described above, in the conventional sensor internal resistance measurement circuit, in order to ensure the measurement range of the internal resistance, that is, the temperature range of the sensor within a predetermined range, three resistors having different resistance values are prepared, Any resistance prepared according to the measurement range is used as the series resistance.

  However, the measurement range of the internal resistance is limited by the series resistance provided, and it is difficult to widen the measurement range. Further, the internal resistance value that can be measured with high accuracy becomes discontinuous, and it is difficult to continuously measure the internal resistance. Furthermore, in order to change the measurement range, the series resistance has to be changed as appropriate according to the measurement range, and much effort has been required.

  The present invention has been made in view of the above, and an object of the present invention is to provide a sensor internal resistance measurement circuit capable of easily expanding the measurement range of the internal resistance and measuring the internal resistance with high accuracy. There is.

  In order to achieve the above object, the invention described in claim 1 is a measurement voltage source that outputs a measurement voltage applied to a sensor, and is output from the measurement voltage source during a measurement operation that measures the internal resistance of the sensor. In a sensor internal resistance measuring circuit, comprising: a switch for selectively supplying the measured voltage to the sensor; and a first measuring means for measuring an output voltage of the sensor, from the measured voltage source to the sensor. And a second measuring means for measuring a drop voltage of the measuring resistance during a measuring operation for measuring the internal resistance of the sensor. And variably controlling the resistance value of the measuring resistor, and measuring the internal resistance of the sensor based on the measurement results of the first and second measuring means and the resistance value of the measuring resistor And having a control means.

  According to the first aspect of the present invention, the measurement range of the internal resistance of the sensor can be expanded over a wide range without reducing the measurement accuracy.

  According to a second aspect of the present invention, in the sensor internal resistance measuring circuit according to the first aspect, the measurement control means is configured to measure the resistance for measurement based on the measurement results of the first measuring means and the second measuring means. The resistance value is variably controlled.

  According to the second aspect of the present invention, the resistance value of the measuring resistor can be variably controlled linearly, and the internal resistance can be measured with high accuracy.

  According to a third aspect of the present invention, in the sensor internal resistance measuring circuit according to the first or second aspect, the measuring resistor connects / disconnects the plurality of resistors arranged in a lattice shape and the plurality of resistors. It is characterized by comprising a switch element.

  According to the third aspect of the present invention, the measurement resistor can be easily constructed with a simple configuration, the resistance value of the measurement resistor can be easily variably controlled, and the internal resistance can be reduced. It can measure with high accuracy.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best embodiment for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a sensor internal resistance measurement circuit according to Embodiment 1 of the present invention. The sensor internal resistance measuring circuit according to the first embodiment shown in FIG. 1 is similar to the conventional example shown in FIG. 2 in that the internal resistance of the sensor 10 is composed of an internal resistance RS whose resistance value changes with temperature and a sensor output power supply VS. This is a circuit for measuring the resistance value of RS. The sensor 10 for measuring the internal resistance RS is, for example, an oxygen sensor that detects an oxygen concentration in exhaust gas. This oxygen sensor is disposed in the middle of an exhaust pipe of, for example, a vehicle and is exhausted from the exhaust pipe. The oxygen concentration contained in the gas is detected. The vehicle feedback-controls the amount of intake air so that the air-fuel ratio A / F, which is the mixing ratio of fuel and air, becomes a predetermined theoretical air-fuel ratio (A / F = 14.7) based on the detected oxygen concentration. doing.

  In FIG. 1, the sensor 10 has a sensor output power supply VS connected to the ground (GND) at the negative electrode side, connected to one end of the internal resistor RS, and the other end of the internal resistor RS connected to one end of the measurement resistor group RV. It is connected.

  The resistance group for measurement RV corresponds to the series resistance RV shown in FIG. The resistance group for measurement RV is a switch in which a number of resistors R are arranged in a ladder shape or a lattice shape, and the connection state of each resistor R is connected / disconnected by a switch element S having a switch function. The element S is configured by, for example, an FET as an example that can be easily configured when the measurement resistance group RV is integrated into an IC. Therefore, the resistance value of the measuring resistor group RV is varied by the connection control of the switch element S. In addition, the resistance group for measurement RV can arbitrarily set a variable range and a variable width of the resistance value that can be varied by the measurement resistance group RV according to the number of resistors constituting the measurement resistance group RV and the connection state. it can. That is, the measurement resistance group RV can be configured so that the resistance value of the measurement resistance group RV can be varied substantially continuously (linearly).

  The other end of the measurement resistor group RV is connected to the positive electrode side of the measurement bias power supply VCC via the switch SW, and the negative electrode side of the measurement bias power supply VCC is connected to the ground (GND). Therefore, the measurement bias power supply VCC functions to apply a reverse bias of the voltage VCC (for example, about 5 V) to the sensor 10. The ground (GND) may be a virtual ground having a potential (VCC / 2) that is ½ of the measurement bias power supply VCC, for example.

  In the sensor 10, the other end of the internal resistor RS is connected to one input terminal of the amplifier AMP1, the other input terminal of the amplifier AMP1 is connected to the ground, and the output terminal of the amplifier AMP1 is connected to the A of the microcomputer (μC) 11. / D conversion port A / D1. Therefore, the amplifier AMP1 measures the voltage at the connection point between the other end of the internal resistor RS and one end of the measurement resistor group RV, that is, the output voltage of the sensor 10, and converts the measured voltage VM into A / D conversion of the microcomputer 11. Apply to port A / D1.

  In the measurement resistor group RV, a connection point with the internal resistor RS of the sensor 10 is connected to one input terminal of the amplifier AMP2, and the other input terminal of the amplifier AMP2 is connected to the positive side of the measurement bias power supply VCC and the positive side thereof. Connected to one end of the connected switch SW, the output terminal of the amplifier AMP2 is connected to the A / D conversion port A / D2 of the microcomputer 11. Therefore, the amplifier AMP2 measures the voltage VR between the connection points of the connection point of the measurement bias power supply VCC and the switch SW, the connection point of the measurement resistance group RV, and the internal resistance RS of the sensor 10, and measures the measured voltage VR. Is supplied to the A / D conversion port A / D2 of the microcomputer 11.

  The microcomputer 11 functions as a control center for the measurement of the internal resistance of the sensor 10 and the resistance value variable control of the measurement resistance group RV, and measures the internal resistance RS based on a control logic program stored therein. Control and resistance value variable control are executed. The microcomputer 11 selectively controls connection / disconnection of the switch SW according to the normal operation of the sensor 10 and the measurement of the internal resistance RS of the sensor 10. That is, the microcomputer 11 turns off the switch SW in the normal operation mode of the sensor 10, while turning on the switch SW in the internal resistance measurement mode of the sensor 10, and detects the sensor from the measurement bias power supply VCC via the switch SW. 10 is applied with a bias voltage.

  The microcomputer 11 has a serial communication function (SPI communication) for serially outputting signals in a time-sharing manner, and a multi-bit control unit that controls on / off of the switch element S via the serial communication port SPI using this function. The switching signal is output serially. The number of bits of the switching signal is appropriately set according to the number of switch elements S constituting the measurement resistance group RV, that is, the number of resistors R constituting the measurement resistance group RV. The microcomputer 11 generates a switching signal according to a desired resistance value to be set in the measurement resistor group RV. Therefore, the microcomputer 11 can recognize the resistance value of the measurement resistor group RV based on the content of the switching signal.

  The microcomputer 11 determines the sensor 10 based on the measurement voltages VR and VM measured by the amplifier AMP1 and the amplifier AMP2 and applied to the A / D conversion ports A / D1 and 2, and the resistance value of the measurement resistance group RV. The internal resistance RS is obtained.

  In the configuration shown in FIG. 1, the components of the measurement circuit excluding the sensor 10 and the microcomputer 11, that is, the measurement resistor group RV, the switch SW, and the amplifiers AMP1 and AMP2 are integrated into an IC.

  In such a configuration, in the normal operation mode of the sensor 10, the switch SW is turned off, the bias voltage VCC is not applied to the sensor 10 from the measurement bias power supply VCC, and the sensor voltage VS output from the sensor 10 is the amplifier AMP1. And the output of the amplifier AMP1 becomes the sensor voltage VS of the sensor 10.

  On the other hand, in the measurement operation mode of the sensor 10 for measuring the internal resistance RS of the sensor 10, first, the sensor voltage VS output from the sensor 10 in the normal operation mode described above is measured by the amplifier AMP1, and the measurement result is sent to the microcomputer 11. Given and stored in internal memory.

  Thereafter, the microcomputer 11 generates a switching signal of the switch element S so that the resistance value corresponds to the resistance value to be detected in the internal resistance RS of the sensor 10, and the generated switching signal is transmitted via the serial communication port SPI. Output. As a result, each switch element S is controlled to be turned on / off, and the connection state of the resistors R constituting the measuring resistor group RV is set so that the resistance value to be detected is obtained.

  In such a state, the switch SW is turned on. As a result, a reverse bias of the voltage VCC is applied from the measurement bias power supply VCC to the sensor 10, and a current I flows from the measurement bias power supply VCC to the sensor 10 via the measurement resistance group RV. At this time, the output voltage of the sensor 10 is measured by the amplifier AMP1, and the measured voltage is VM. Further, the voltage of the resistance group for measurement RV and the switch SW connected in series is measured by the amplifier AMP2, and the measured voltage is set to VR. The measured voltages VM and VR are given to the microcomputer 11.

  The microcomputer 11 determines the resistance value of the measurement resistor group RV so that the relationship between the measured voltages VM and VR and the sensor voltage VS of the sensor output power source VS of the sensor 10 is (VR = VM−VS). The operation to be adjusted is executed by feedback control. When the adjustment of the resistance value of the measurement resistor group RV is performed and the relationship of (VR = VM-VS) is established, the voltage drop of the measurement resistor group RV including the switch SW due to the current I and the sensor The voltage drop of 10 internal resistances RS becomes equal. Thus, the internal resistance RS is obtained as the resistance value of the measurement resistance group RV recognized based on the switching signal output from the microcomputer 11.

  When the measurement of the internal resistance RS is completed, the switch SW is turned off, all the switch elements S of the measurement resistance group RV are turned off, and the sensor 10 is set in the normal operation mode.

  As described above, in the sensor internal resistance measurement circuit according to the first embodiment, the measurement range of the internal resistance RS of the sensor 10 can be set according to the variable range of the resistance value of the measurement resistor group RV. Without making it possible, the measurement range of the internal resistance can be expanded over a wider range than before. Accordingly, it is possible to deal with sensors having different internal resistance characteristics, that is, sensors having various characteristics having different temperature ranges of the sensors, and it is possible to provide a measurement circuit having excellent versatility.

  Furthermore, the internal resistance RS can be measured linearly by linearly varying the resistance value of the measurement resistor group RV. Thereby, the internal resistance RS can be measured with high accuracy.

  Instead of the measurement resistance group RV, a variable current source having a function equivalent to that of the measurement resistance group RV may be employed in measuring the internal resistance of the sensor 10 by varying the current.

It is a figure which shows the structure of the sensor internal resistance measuring circuit which concerns on Example 1 of this invention. It is a figure which shows the structure of the conventional sensor internal resistance measurement circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 20 ... Sensor 11, 22 ... Microcomputer 21, AMP1, AMP2 ... Amplifier A / D, A / D1, A / D2 ... Conversion port R ... Resistance RS ... Internal resistance RV ... Resistance group for measurement S ... Switch element SPI ... Serial communication port SW ... Switch VCC ... Bias power supply for measurement VG ... Bias power supply VS ... Sensor output power supply

Claims (3)

A measurement voltage source for outputting a measurement voltage applied to the sensor;
A switch that selectively provides the sensor with a measurement voltage output from the measurement voltage source during a measurement operation of measuring the internal resistance of the sensor;
In the sensor internal resistance measurement circuit comprising a first measuring means for measuring the output voltage of the sensor,
A resistance for measurement provided in a flow path of a current supplied from the measurement voltage source to the sensor via the switch, the resistance value being variable;
A second measuring means for measuring a drop voltage of the measuring resistor during a measuring operation for measuring the internal resistance of the sensor;
Measurement control means for variably controlling the resistance value of the measurement resistor and obtaining the internal resistance of the sensor based on the measurement results of the first and second measurement means and the resistance value of the measurement resistance. A sensor internal resistance measuring circuit. 2. The sensor internal resistance measurement according to claim 1, wherein the measurement control unit variably controls a resistance value of the measurement resistor based on measurement results of the first measurement unit and the second measurement unit. circuit. 3. The sensor internal resistance according to claim 1, wherein the measurement resistor includes a plurality of resistors arranged in a grid pattern and a switch element that connects / disconnects the plurality of resistors. 4. Measuring circuit.

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