DE2918961A1 - EVALUATION FOR AN INDUCTIVE SHORT-CIRCUIT SENSOR - Google Patents

Description

R. 5464

6.4.1979 Lr / Sm

ROBERT BOSCH GMBH, 7OOO Stuttgart 1

Evaluation circuit for an inductive short-circuit ring displacement encoder

The invention relates to an evaluation circuit for an inductive short-circuit ring displacement transducer, with the generic term of the claim specified features.

From DE-OS 24 16 237 an evaluation circuit for an inductive short-circuit ring displacement encoder is known at which the inductance having a path-dependent variable inductance to the output of a voltage comparator connected operational amplifier and connected to the other end of the winding with one Resistor connected to ground is connected and via a feedback line to the inverting input of the operational amplifier is connected, while the non-inverting input is connected to the tap of an off two resistors existing voltage divider is connected. The comparator generates a square wave more constant Amplitude with a frequency that is inversely proportional to the path to be measured and the inductance is. The period of the square wave is therefore proportional to the path to be measured.

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The invention is based on the object of accuracy the evaluation of the variable inductance by comparison with the inductance of a second coil raise. For this are the. in the characterizing part of claim 1 specified measures provided.

The invention is described in more detail below with the aid of several exemplary embodiments that are shown in the drawing described and explained.

Figure 1 shows an inductive displacement encoder, which the. Adjustment path of a membrane 1 in a change in the Converts the inductance of a coil 2, which is arranged on the center leg 3 of an iron core 4. the Membrane 1 is pressure-tightly connected to a housing 5, the interior of which is connected to the intake pipe via a pipe socket 6 is connected to an internal combustion engine, not shown, and is intended to serve the prevailing there, Intake air pressure dependent on the driving speed, the throttle valve position and the load condition of the internal combustion engine to convert into an analog electrical variable with which an operating variable of the internal combustion engine, For example, the ignition adjustment angle or the amount of fuel injected depends on the prevailing one Operating conditions can be adapted. ·

In the housing 5, a coil spring 7 is arranged, on the one hand bears against the membrane 1 and on the other hand against the housing 5 · and is disposed coaxially with a stop _8a by means of a screw ™ thread 9 can be adjusted in the axial direction and the displacement s of the membrane center.

In the center of the membrane 1 sits a tubular, made of insulating material manufactured carrier 10 for one on his

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ORIGINAL INSPECTED

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Front side attached short-circuit ring 11, which engages around the middle leg 3 and the inductance of the coil 2- The greater the pressure in the suction pipe, the more it increases and accordingly the pressure prevailing in the housing 5 falls relative to the external atmospheric pressure and the more it increases while the center of the membrane 1 is moved in the direction of the arrow s.

In order to convert the changes in the inductance Ll of the coil 2 into a square wave when the path s changes To be able to convert 12, an evaluation circuit 13, described in more detail below, is provided, with which is an analog signal U. can be won.

According to the invention, the evaluation circuit can be constructed according to the circuit diagram shown in FIG. The main components of this evaluation circuit are an operational amplifier O ₅ used as a voltage comparator, a bistable flip-flop FF with two opposing outputs Q and Q and two switching transistors T1 and T2, which are used to alternately connect the coil 2 of the inductive displacement sensor according to FIG its variable inductance Ll and then a second coil 15s whose inductance L2 can be set to a fixed value to be switched into the control circuit of the voltage comparator 0 '. For this purpose, the two coils 2 and 15 are fed to a common connection point 16 and connected to a resistor R leading to the common operating current line 17 connected to the positive pulse of a vehicle battery (not shown) and also connected via a line 18 to the inverting input 20 of the voltage comparator 0. This is via a "decoupling resistor 21 as well as the plus input

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passage 22 of the comparator via a decoupling resistor connected to the tap of a voltage divider formed from two resistors 24 and 25. From the plus input of the comparator 0 also leads a resistor 26 to ground.

From the collector of the two transistors T1 and T2 connected to the coils 2 and 15, respectively, a diode D1 and D2 leads to the cathode of a Zener diode Z _3, the anode of which is connected to the two coils and the resistor R.

The transistors T1 and T2 acting as switches control the coils 2 and 15 alternately. The voltage picked up across the resistor R is proportional to the current flowing through the respectively activated coil, the course of which is indicated in FIG. 3 by the line 27. If U _ß denotes the voltage on the plus line 17, a control voltage U _g according to the equation results at the minus input 20 of the comparator 0

^Ü S ' ^{= L} l / 2 * = 1 * ¹

^{R t} l / 2

where t ^ / tp means the duty cycle of the square wave.

If the voltage falls below the threshold voltage set on the comparator 0 ^ it switches its output to positive supply voltage. The subsequent flip-flop changes its initial state and thus controls the other coil via the corresponding transistor T1 or T2. While the current is extinguished in the non-activated coil via the associated diode Dl ₅ D2 and the Zener diode Z, the activated coil integrates the

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Current proportional to their inductance up to the threshold voltage of the comparator is reached again.

If the square-wave voltage shown in the top line in FIG. 3 is used at the Q output of the flip-flop FF, which is shown by the line 28 in Figure 3, is obtained by reshaping the above equation:

^U r τ

This means that the pulse duration t. proportional to Inductance Ll and the pause time t ~ proportional to Inductance L2 of the comparison coil 15 is. The output signal indicated in the figure at U "can be digital as can also be processed in an analogous manner by averaging. For a digital evaluation the at the output of the comparator 0 resulting switching pulses 29 are used, which in the bottom line of Figure 3 are indicated.

In Figure 4, a second inductive short-circuit ring encoder is shown, which is designed as a differential angle encoder and allows the conversion of the angle of rotation cK, a shaft 30, for example the throttle valve shaft of an internal combustion engine into an analog electrical variable.

In detail, the rotary encoder according to Figure 4 has two mutually concentric, semi-cylindrical ring segments 31 and 32, which are connected to one another by radial magnetic webs 33 and 34. One of two coils 35 and 36, whose inductances are Ll and L2, respectively, is seated close to these webs

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are designated. On the shaft 30, 37 is seated, a cantilever made of metal, which ends in a short-circuit ring 38 ₃ which encloses the outer ring segment 31 and the inductors Ll and L2 of the two coils 35 and 36 are changed in the opposite direction during the rotational movement of the shaft 30, namely the inductance of the coil 35 is reduced, while at the same time the inductance L2 of the coil 36 is increased and vice versa.

To evaluate the two as a function of the swivel angle o (variable inductances L1 and L2, the circuit shown in Figure 2 can be used. Another evaluation circuit is shown in FIG. which also oscillates automatically and produces an output voltage U at its output A, which is analogous to the clock ratio, is frequency-analog and / or period-analog.

In detail, the evaluation attitude according to Figure 5, in which the components that correspond to the circuit according to FIG. 3 are provided with the same reference numerals are the operational amplifier used as a voltage comparator 0, two switching amplifiers Sl and S2 for the two inductors Ll and L2 soifie one between the Output of the operational amplifier 0 and the input of the flip-flop FF connected clock amplifier V and two with the outputs Q and § switched isolation amplifiers Pl and P2.

The evaluation circuit according to FIG. 5 works in principle in the same way as that according to FIG. _3S, so that a detailed functional description is superfluous.

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Claims (1)

6 Λ. 1979 Lr / Sm ROBERT BOSCH GMBH, 7OOO Stuttgart 1 claim Evaluation circuit for an inductive short-circuit ring displacement encoder, which carries a coil on an iron core, the inductance of which can also be changed by a short-circuit ring, which includes one leg of the iron core and is displaceable along this leg by a distance, whose respective size is converted into an analog electrical signal, in particular a voltage, with the help of an operational amplifier connected as a voltage comparator, the one in its period duration of the respective inductance value of the coil-dependent square wave generated, characterized in that the A flip-flop is connected downstream of the comparator, at whose two outputs (Q, Q) each one of two switching transistors connected, one of which is the variable inductance coil and the other of which is the transistor a second, for comparison. Coil alternately in one lying at the input of the comparator Circuit switches on. 03Ö047 / 02GS