FR2750506A1 - DEVICE FOR MEASURING, WITH LOST LITTLE POWER, A HEATING INTENSITY THROUGH A PROBE HEATING DEVICE - Google Patents

Abstract

Device for measuring, with little power loss, a heating current (IH) passing through a probe heater (10), a comparison taking place, in a circuit unit (50), between a voltage (UM) applied to a measuring resistor (20) connected in series with the probe heater (10), and a reference voltage (UR) applied to a reference resistor (30) through which a constant reference current (IR) carries and having the same signal mode as the measuring resistor (20). The measuring resistor (20) comprises a number of resistance elements (21), connected in parallel, each of which substantially corresponds to the reference resistor (30) with respect to its dimensions and electrical properties.

Description

STATE OF THE ART The invention relates to a device for measuring,

  by losing little power, a heating intensity not

  health through a probe heater, a com-

  parison taking place, in a circuit unit, between a voltage applied to a measurement resistor connected in series with the probe heater, and a reference voltage applied to a reference resistance traversed by a constant reference current and having the

  same signal mode as the measurement resistor.

  A device of this type appears for example from document EP-0 506 668 B1, the content of which is incorporated into the

this request.

  It is known to maintain an air / fuel ratio

  determined rant of the air / fuel mixture supplied to a

  internal combustion, regulating devices which receive

  wind their adjustment quantity of an oxygen measurement probe placed in the exhaust system of the combustion engine

  internal. Oxygen sensors of this type do not work

  operate without problem that from a working temperature

determined operation.

  For this reason, probe heaters are known which heat the probe in particular at

  cold start and during the warm-up phase of the engine

internal combustion engine.

  So that the probe reaches as quickly as possible

  ble its operating temperature and then can be

  also maintained at a predefined temperature, must guarantee

  derives the correct functioning of the probe heating. In addition the probe can be destroyed when it passes through it an intensity of value greater than that of an intensity

maximum allowable.

  It follows from the document mentioned

  above EP-0 506 668 B1, a method and a device used

  to check the correct functioning of a probe heater, in the case of which the current which passes through the probe heater is detected continuously by a comparison between a voltage applied to

  a measurement resistor connected in series with respect to the

  positive probe heating, and a reference voltage

  applied to a reference resistance traversed by an in-

  constant reference density and having the same mode of signals as the measurement resistance which is modified or disconnected if necessary. The measurement resistance that we come in this

  case to use, both with regard to its geometrical dimensions

  triques that with regard to its electrical properties, in

  particularly for the detection of bran intensity peaks

  larger permanent currents, must be designed to be significantly larger than the reference resistance which is only traversed by an intensity

relatively small constant.

  For example, the resistance of me-

  sure must, in the case of configuration most often

  used, present itself as a resistance with layers

  killed on a support a width substantially greater than

  the reference resistance, while otherwise having a long

  substantially concordant thickness and thickness.

  This has the disadvantageous consequence

  that for example the tolerances imposed by the fa-

  brication in the case of the same manufacture for resistance

  tance measurement and the reference resistance, lead to a very large measurement error of the heating intensity without significant loss of power, because tolerances of this

  type, which are identical in principle in the case of re-

  reference resistance and in the case of the resistance of

  due to the larger configuration of the measurement resistance, in percentage, in the case of the latter, has a smaller influence on the measurement results than

  in the case of the reference resistance which has a configuration

  smaller ration and in which an error has effects

significantly stronger.

  For example, a fault can be monitored

  when manufacturing the measurement resistor and the reference resistor, in the case of their constitution in the form, seen in absolute terms, of film resistors, in the form of a variation in length respectively identical in the case of the measurement resistor and in the

  case of the reference resistance, due to the method of fa-

  brication. However, as the pre-

  feels of dimensions smaller than the measurement resistance, this defect, expressed in percentage, is appreciably more important in the case of the reference resistance than

  in the case of the measurement resistor.

  The object of the invention is therefore to improve

  rer a device used to measure, losing little power

  sance, a heating intensity passing through a probe heating device of the type mentioned above, so that this makes it possible to obtain, in the case of simple manufacture, substantially more precision.

high for measurement.

  Advantages of the invention This problem is solved in the case of a device used to measure, with little power loss, a heating intensity passing through a probe heating device, thanks to the fact that the measuring resistor comprises a number of resistance elements, mounted in parallel,

  each of which corresponds substantially to the reference resistance

  with regard to its dimensions and its electrical properties. The constitution of the measurement resistor in the form of a number of mounted resistance elements

  in parallel, each of which corresponds substantially to the resistance

  reference tance with regard to its dimensions and

  electrical properties, offers the great advantage that for example-

  ple manufacturing faults, which occur in the case of each resistance element, thus add up independently of the number of resistance elements. This actually increases the overall fault of the measurement resistor but, by this configuration of the measurement resistor, we

  arrives at the same percentage of de-

  only the reference resistance. As we come to

  measure the heating intensity which passes through the device

  positive probe heating, substantially only as a function of the relationship between the reference resistance and the

  measurement resistance, with regard to the ratio,

  wearing resistors, an error that almost disappears in

  the case of an identical defect, in percentage, of the resistance

  reference tance and measurement resistance.

  Purely in principle, one can constitute the re-

  measurement resistance and reference resistance in a wide variety of ways. In particular, to obtain the same signal mode from the reference resistance and the measurement resistance, and in particular also to maintain the reference resistance and the measurement resistance at an analogous temperature and to obtain a good agreement,

  with regard to dimensions and electrical properties

  ques of each of the different resistance elements with the reference resistance, it is advantageously provided that the reference resistance and the elements of the measurement resistance are film resistors, arranged on a

common substrate.

  These layer resistors (layer resistors

  thin / thick) are electrical resistors which are fa-

  bricked by the structuring of a material electrically

  conductive (for example a metal). This electrical matter-

  conductive can be put on a substrate by metalli-

  vacuum, spray, galvanic or other physical / chemical process known to

one skilled in the art in this field.

  By manufacturing the measurement resistor and the

  reference resistance from the same electrical material-

  conductive and by placing it on the same substrate,

  has the assurance that the reference resistance and all the elements

  The measuring resistance, and in this way also the measuring resistance, are kept at about the same temperature and exhibit similar temperature behavior. For this reason, the reference resistor and the elements of the measuring resistor are arranged on the substrate so that they are as close as possible to the

each other.

  According to an advantageous embodiment of the invention, provision is made for the reference resistor to be formed in the form of a fine conductive track, the dimensions of which result from the determination of the constant intensity and of the control thresholds.

  The elements of the measuring resistance are also

  preferably formed so as to be arranged in a

  rally to each other and to be disposed closely

one next to the other.

  Drawings The present invention will be described below in more detail on the basis of embodiments, represented in the appended drawings in which: - Figure 1 schematically shows a device according to the invention used for measuring, losing little power , a heating intensity passing through a probe heater; and FIG. 2 shows a device known from the state of the art used to measure, with little power loss, a heating intensity passing through a device

probe heating.

  Description of the exemplary embodiments

  FIG. 2 shows a device

  known from the state of the art, used to measure, in

  with little power, a heating intensity passing to

  through a probe heater. As it res-

  as shown in FIG. 2, the device comprises a device for

  heating of probe 10 which is traversed by an intensity IH.

  A measuring resistor 20 is connected in series with this device.

  heating probe 10 positive, measurement resistor which for example is formed in the form of a layer resistor (thin / thick layer resistor) arranged on a substrate. In the vicinity of the measurement resistor 20, a reference resistor 30 is placed on the substrate, for example in the form of a layer resistance traversed by a constant reference intensity IR produced by a constant reference intensity source 40 UR tension

  which is taken from the reference resistor 30 and the voltage

  Zion UM which is taken from the measurement resistor 20, are brought for comparison to a circuit unit 50 in which the difference between the two voltages UM and UR is formed and it is evaluated. This evaluation is described in detail in document EP-0 506 668 B1, the content of which is incorporated into the

  this request. The reference resistor 30 is usually formed in the form of a thin conductive track, tan-

  say that the measurement resistor 20 which is used to determine peaks of connection intensity and permissible intensities

  nentes larger, is made in the form of a conductive track as short and as wide as possible, as indicated schematically in Figure 2.15 The described embodiment of the measurement, with low power loss, of the intensity heating element IH passing through a probe heating device 10, then has a defect of up to 25%, the main fraction of this defect coming from manufacturing tolerances during the production of the layer resistance. This is how

  example that when manufacturing the resistance to

  In the form of conductive tracks by etching, it is possible to have a defect, during manufacture, which can vary between 10 Am and 30 gm. In this case we can start from

  fact that the fault is constant over a small area of the subs

  trat. If then for example the reference resistor is constituted in the form of a conductive track having a width of 160 pm, an absolute defect of for example -30 gm

  corresponds to a defect, in percentage of 18.75%. If in or-

  tre the measurement resistor has a width of conductive track which corresponds for example to 19 times that of the reference resistance, that is to say 3040 Lm, it occurs in the case of a deviation of -30 gm from made of engraving, a

default of 0.99%.

  As for determining the heating intensity we

  significantly exploits the relationship between the value of the resistance

  reference voltage 30 and that of the measurement resistor 20, in this way, in the report, an error of

  17.76% which in practice is caused exclusively by the

  faults different from the reference resistance and the

measuring resistance.

  In Figure 1 there is shown schematically-

  tick a device according to the invention for measuring, with little power loss, a heating intensity passing through a probe heating device, in the case

  of which this difference error is in practice complete-

  eliminated. This is achieved by the fact that by comparison

  sound with the device shown in Figure 2, the measurement resistor 20 is to some extent broken down into a number of resistance elements 21, mounted in

  parallel, each of which corresponds substantially to the resistance

  reference tance 30 with regard to its dimensions and electrical properties. These resistance elements 21 are for example constituted, like the reference resistance, in the form of film resistors constituted in the form of fine conductive tracks arranged closely in the vicinity of the reference resistance 30, and placed in parallel with one another. closely next to each other, as shown schematically in Figure 1.

  In the case of this configuration of the resistance

  measurement tance 20, there is then a fault originating from

  manufacturing example, defect for example due to tolerances

  these of etching in the case of a manufacturing by etching, for each of the resistance elements 21. As then each of the resistance elements 21 corresponds, as regards

  its dimensions as in terms of its electrical properties

  triques, substantially on the conductive track of the resistance

  30, the faults of each of the resistance elements

  tance 21 add up to some extent such

  so that the fault, as a percentage of the resistance of the

  on 20, corresponds in the case of this configuration to the

  as a percentage of the reference resistance, thanks to

  whereby a defect of the ratio of practically zero is obtained.

  Thanks to precise manufacturing of the resistance elements lying close to each other,

  in the form of resistant tracks, on the substrate,

  takes in practice an error, in percentage, of the resistance ratio, which is between 1 and 2%, this error being therefore much lower than in the case of the known device of the state of the art and represented on the figure 2.

Claims (5)

R E V E N D I C A T IONS   1) Device for measuring, with little power loss, a heating intensity (IH) passing through a probe heating device (10), a comparison taking place, in a circuit unit (50), between a voltage ( UM) applied to   a measuring resistor (20) connected in series with the device   probe heating device (10), and a reference voltage (UR) applied to a reference resistance (30) traversed by a constant reference intensity (IR) and having the same mode of signals as the measurement resistance (20 ) characterized in that the measuring resistor (20) comprises a number   resistance elements (21), mounted in parallel, each of which   cun corresponds substantially to the reference resistance (30)   with regard to its dimensions and electrical properties   ques. 2) Device according to claim 1, characterized in that the reference resistor (30) and the resistance elements (21) of the measurement resistor (20) are resistors to   layers arranged on a common substrate.   3) Device according to claim 1 or 2, characterized in that the reference resistance (30) and the resistance elements   (21) are arranged on the substrate being closely placed side by side.   4) Device according to one of the preceding claims,   characterized in that the reference resistor (30) is formed in the form of a fine conductive track.   5) Device according to one of claims 1 to 3,   characterized in that the resistance elements (21) are formed in the form of thin conductive tracks mounted in parallel with one another and arranged closely together side of others. f