JPH1068745A - Measuring device with which power loss of heating current flowing in probe heating device is small - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a measuring device with which the power loss of heating current flowing in a probe heating device is small to be manufactured easily and have substantially high measuring accuracy. SOLUTION: In a measuring device with which the power loss of heating current flowing in a probe heating device is small, a comparison between a voltage which drops at a measuring resistance 20 inserted in series into the probe heating device 10 and a reference voltage which drops at a reference resistance 30 through which a constant reference current flows and which has the same signal characteristic as the measuring resistance 20 is made by a circuit unit 50. The measuring resistance 20 includes a plurality of resistance elements 21 arranged in parallel, each of the resistance elements 21 almost matching the reference resistance 30 in size and electric characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a voltage drop across a measurement resistor inserted in series with a probe heating device;
A power loss of the heating current flowing through the probe heating device, wherein a comparison between the measuring resistor and a reference voltage falling at the reference resistor having the same signal characteristics is made in the circuit unit, wherein a constant reference current flows. Is related to a small measuring device.

[0002]

2. Description of the Related Art Such a device is described, for example, in European patent B
No. 1,506,668, the contents of which are incorporated by reference into the present patent application.

[0003] In order to maintain a predetermined air / fuel ratio of the air / fuel mixture supplied to the internal combustion engine, control devices are known whose control variable is obtained from an oximeter probe provided in the exhaust system of the internal combustion engine. Such an oximetry probe will only operate without problems above a certain operating temperature.

For this reason, especially during cold start and during the warm-up process of the internal combustion engine,
Probe heating devices for heating probes are known.

[0005] The function of the probe heating must be ensured in such a way that the probe reaches its operating temperature as quickly as possible and can thereafter be maintained at the predetermined temperature. In addition, the probe may break if a current greater than the maximum allowable current flows through the probe heating device.

Accordingly, the above-mentioned European Patent No. B1 050
No. 6668 discloses a method and a device for monitoring the function of a probe heating device, in which a voltage drop at a measuring resistor arranged in series with the probe heating device, a constant reference current flows and the measurement is carried out. By means of a comparison between the resistance and a reference voltage falling at a reference resistance having the same signal characteristics, the current flowing through the probe heating device is continuously measured, possibly changed or interrupted.

The measuring resistor used here is a reference for a relatively small constant current, not only with regard to its geometric dimensions but also its electrical properties, in order to measure particularly large input current peaks and sustaining currents. Must be designed to be substantially larger than the resistance.

[0008] Thus, for example, if the measured resistance is formed as a film resistance on a carrier, as often used, it will typically have a substantially larger width than the reference resistance if it has approximately the same length and thickness. Must have.

As a result, the disadvantage is that tolerances arising, for example, during the production of the measuring resistor and the reference resistor in the same way lead to very large measuring errors for heating current measurements with small power losses. . The reason is that such tolerances, which are the same as absolute values in the reference and measured resistances, are formed substantially smaller by making the measured resistance larger, and more so in the reference resistance where the error has a substantially larger effect. This has only a relatively small effect on the measured resistance.

Therefore, for example, when the film resistance is formed as a film resistance whose length is changed as an absolute value, the same error can be given to the measured resistance and the reference resistance based on the manufacturing process. However, since the reference resistance has a smaller dimension than the measured resistance, this error will be a substantially much lower percentage ratio than the measured resistance.

[0011]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a measuring device in which the power loss of the heating current flowing through the probe heating device is small, so that it is simple to manufacture and allows a substantially higher measuring accuracy. This is the subject of the present invention.

[0012]

SUMMARY OF THE INVENTION According to the present invention, an object of the present invention is to provide a measuring device in which the heating current flowing through the probe heating device has a small power loss. And each of the resistive elements substantially corresponds to a reference resistance with respect to its dimensions and its electrical properties.

The fact that the measuring resistance is formed as a plurality of resistance elements arranged in parallel, each of which substantially corresponds to a reference resistance with regard to its dimensions and its electrical properties, means that, for example, errors due to the manufacture are not equal to each resistance. It has the great advantage that it occurs in the elements and is added as a function of the number of resistance elements. This does increase the total error of the measured resistance, but by forming the measured resistance in this way, the measured resistance will have the same percentage error as the reference resistance. Since the ratio of the reference resistance to the measured resistance is important for the measurement of the heating current flowing through the probe heating device, if the reference resistance and the measured resistance have the same percent error, the resistance relative error almost canceled out. Is obtained.

[0014] Purely in principle, the measuring resistor and the reference resistor may be formed in different types. In order to obtain the same signal characteristics from the reference and measurement resistors, in particular to keep the reference and measurement resistors at the same temperature, and to make sure that the dimensions and electrical characteristics of each resistance element match those of the reference resistance. To obtain it, it is advantageous to design the resistance elements of the reference resistance and the measurement resistance as film resistors arranged on a common substrate.

These film resistances (thin film resistance / thick film resistance) are electric resistances formed by the structure of a conductive material (eg, metal). This conductive material, by evaporation,
It can be formed on the substrate by sputtering, by electrolysis, or by other physical / chemical processes known to those skilled in the art.

By fabricating the measured and reference resistors from the same conductive material of the same thickness and by arranging them on the same substrate, all the resistance elements of the reference and measured resistors, and thus also the measured resistance, It is ensured that they are kept at substantially the same temperature and have the same temperature characteristics.

For this reason, the resistance elements of the reference resistance and the measuring resistance are arranged particularly closely adjacent on the substrate.

In a preferred embodiment, the reference resistor is formed as a thin conductor track, the dimensions of which are given by the determination of the constant current and the monitoring threshold.

The resistance elements of the measuring resistor are likewise preferably formed as thin conductor tracks arranged parallel to one another and closely adjacent to one another.

[0020] Other features and advantages of the invention will be apparent from the following description and drawings of certain embodiments.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows a measuring device having a small power loss of a heating current flowing through a probe heating device known from the prior art. As is clear from FIG. 2, this measuring device includes a probe heating device 10 through which a current IH flows. A measuring resistor 20 is inserted in series with the probe heating device 10, and the measuring resistor 20 is formed, for example, as a film resistor (thin film resistance / thick film resistance) disposed on a substrate.

A reference resistor 30 formed, for example, as a film resistor is arranged adjacent to the measuring resistor 20, and a constant reference current IR flows through the reference resistor 30, and the constant reference current IR is a reference constant current source. Generated by. The voltage drop UR via the reference resistor 30 and the voltage drop UM via the measuring resistor 20 are used for comparison in the circuit unit 50.
And the difference between the two voltages UM and UR is formed and evaluated in the circuit unit 50. This evaluation is described in EP 1 506 668, the content of which is referenced in the present application.

The reference resistor 30 is typically formed as a thin conductor track, while the measuring resistor 20 is as short and short as possible, as shown schematically in FIG. 2, to measure larger input and peak currents. It is formed as a wide conductor track.

Heating current I flowing through probe heating device 10
The illustrated design, which makes measurements with low power loss in H, now has an error of less than or equal to 25%, where the major part of this error is due to manufacturing tolerances when manufacturing film resistors. Thus, for example, when producing film resistors in the form of conductor tracks by etching, 10 μm and −30 μm
There is a possibility that a manufacturing error that varies in the range of? In this case, it is assumed that the error is constant over a small area of the substrate. Here, for example, the reference resistance is 160 μ
When formed as a conductor track having a width of m, an absolute error of, for example, -30 .mu.m corresponds to a percentage error of 18.75%. Here, furthermore, if the measured resistance has a conductor path width corresponding to, for example, 19 times the reference resistance, ie 3,040 μm, a -30 μm error due to etching results in a 0.99% percent error.

In order to determine the heating current, the resistance ratio between the reference resistance 30 and the measurement resistance 20 is substantially evaluated.
A relative error of 7.76% is obtained, and this relative error is actually obtained only by the relative error between the reference resistance and the measured resistance.

FIG. 1 shows a measuring device in which the power loss of the heating current IH flowing through the probe heating device is small, in which this relative error is practically completely eliminated. This means that, compared to the device shown in FIG. 2, the measuring resistor 20 is formed as a plurality of resistance elements 21 arranged in a so-called parallel manner, each of these resistance elements 21 being substantially standard with respect to its dimensions and its electrical properties. It corresponds to the resistor 30. This resistive element 21 is, for example, in the form of a parallel thin conductor track, as shown schematically in FIG. It is formed as a film resistor.

When the measuring resistor 20 is formed in this way,
For example, an error due to manufacturing, for example, the above-described etching tolerance when manufactured by etching, is caused by the resistance element 21.
Occurs in each of the. Here, since each of the resistance elements 21 substantially corresponds to the conductor path of the reference resistance 30 in terms of its dimensions and electrical properties, the errors of the individual resistance elements 21 are so-called added, and thus the so formed The percent error of the measured resistor 20 corresponds to the percent error of the reference resistor, which actually results in a relative error of 0%.

By accurately fabricating the resistive elements closely adjacent to each other in the form of a resistive path on the substrate, a relative resistance error in the range of 1 to 2% is actually obtained, and therefore a relative resistance error of the percent. Is much smaller than in the device shown in FIG. 2 known from the prior art.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a measuring device according to the present invention, in which a power loss of a heating current flowing through a probe heating device is small.

FIG. 2 is a schematic diagram of a measuring device known from the prior art, in which the power loss of the heating current flowing through the probe heating device is small.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 probe heating device 20 measurement resistor 21 resistance element 30 reference resistor 40 reference constant current source 50 circuit unit I current IH heating current IR constant reference current UM voltage drop at measurement resistor UR reference voltage drop at reference resistor

Claims (5)

[Claims] 1. A voltage drop (UM) at a measuring resistor (20) inserted in series with a probe heating device (10).
And a constant reference current (IR) flows and the measured resistance (2
0) and a reference voltage (UR) falling at a reference resistor (30) having the same signal characteristics, a comparison is made in the circuit unit (50) of the heating current (IH) flowing through the probe heating device (10). In a measuring device with low power loss, the measuring resistor (20) comprises a plurality of resistive elements (21) arranged in parallel, each of the resistive elements (21) relating to its dimensions and its electrical properties to a reference resistor (30). A measuring device having a small power loss of a heating current flowing through a probe heating device, which is substantially compatible. 2. A reference resistance (30) and a measured resistance (2).
2. The measuring device according to claim 1, wherein the resistive element (0) is a film resistor disposed on a common substrate. 3. A reference resistance (30) and a resistance element (2).
3. The measuring device according to claim 1, wherein 1) is arranged closely adjacent to the substrate. 4. The measuring device according to claim 1, wherein the reference resistor is formed as a thin conductor track. 5. The measuring device according to claim 1, wherein the resistance elements are formed as thin conductor tracks arranged parallel to one another and closely adjacent to one another. .