WO2002033357A1

WO2002033357A1 - Determination and/or evaluation of an analog measuring variable

Info

Publication number: WO2002033357A1
Application number: PCT/EP2001/011816
Authority: WO
Inventors: Andreas Krug; Carlhermann Schlehaus
Original assignee: Wittenstein Ag
Priority date: 2000-10-17
Filing date: 2001-10-12
Publication date: 2002-04-25
Also published as: AU2002223613A1; DE10056806A1

Abstract

Disclosed is a device (10, 20) for determination and/or evaluation of an analog measuring variable, comprising an electronic measuring element (30) which is acted upon by said measuring variable, and a circuit unit (40) which along with the measuring element (30) is coupled to form a measuring circuit (20), the measuring circuit (20) having a non-linear characteristic. A signal unit (10) is provided in order to impinge an input signal (50) upon the measuring circuit (20), and an evaluation unit (10) which is coupled to the measuring circuit (20) evaluates a signal response (60) to the input signal from the signal unit (10). The evaluation unit has a comparator which is used to compare the signal response (60) to a threshold value (Uth), means for determining the delay time between attainment of the threshold valve (Uth) and a corresponding instant of the input signal.

Description

Determination and / or evaluation of an analog measured variable

The present invention relates to the determination and / or evaluation of an analog measured variable, such as temperature, force, pressure or displacement, which acts on an electronic measuring element.

For the determination and / or evaluation of such analog measurement variables, they are typically first recorded with a sensor as an electronic measuring element, digitized via an analog / digital converter and then further processed digitally.

An alternative to this is the use of voltage-controlled oscillators (VCO), as is the case, for example, in the published patent application DE-A-44Q8898 is described.

The present invention is also based on the object of determining and / or determining analog measurement variables, such as temperature, force, pressure or displacement.

The present invention provides a device for determining and / or evaluating an analog measurement variable, such as preferably temperature, force, pressure or displacement, which acts on an electronic measuring element. For this purpose, the device has a circuit unit, which is coupled to the measuring element to form a measuring circuit, and an evaluation unit, which is coupled to the measuring circuit, for evaluating a signal response to an input signal acting on the measuring circuit. The measuring circuit has a non-linear electrical characteristic, which is known in its essential characteristics. The evaluation unit also has means for checking the signal response for reaching a threshold value, means for determining a transit time between reaching the threshold value and a corresponding point in time of the input signal, and means for determining and / or evaluating the analog measured variable from the determined transit time and the essentially known electrical characteristic of the measuring circuit.

The invention thus uses the signal change and delay caused by a non-linear circuit in order to draw conclusions from this on the measurement variable. A delay time compared to the input signal is determined by simple threshold value formation. The delay time in turn is dependent on the actual values of the circuit elements, so that, conversely, the delay time in the case of a known one Characteristic the actual values of the circuit elements can be determined.

In a preferred embodiment, the corresponding point in time of the input signal is determined by an edge of the input signal, preferably if the input signal is a digital signal. Such signal edges allow a simple and reliable assignment of a defined start time to which the delay time can refer.

The measuring circuit is preferably an RC circuit or an RL circuit of the first degree. As a result, the circuitry and evaluation effort can be kept as simple and low as possible.

According to the invention, the determination and / or evaluation of an analog measurement variable, such as preferably temperature, force, pressure or displacement, which acts on an electronic measurement element, the measurement element being coupled to a circuit unit for a measurement circuit, and the measurement circuit being a non-linear one has electrical characteristic that is essentially known; with the steps:

Checking a signal response to an input signal acting on the measuring circuit for reaching a threshold value,

• Determining a transit time between reaching the threshold value and a corresponding point in time of the input signal, and

• Determination and / or evaluation of the analog measured variable from the determined transit time and the essentially known electrical characteristic of the measuring circuit.

Another preferred embodiment of the invention has an electronic measuring element on which the measured variable acts and a circuit unit which is coupled to the measuring element to form a measuring circuit. The measuring circuit has a non-linear electrical characteristic which is known in its essential characteristics. A signal unit is provided to apply an input signal to the measuring circuit, and an evaluation unit coupled to the measuring circuit is used by the signal unit to evaluate a signal response to the input signal. The evaluation unit has a comparator for comparing the signal response with a threshold value, means for determining a transit time between reaching the threshold value and a corresponding point in time of the input signal, and means for determining and / or evaluating the analog measured variable from the determined transit time and the im Mainly known electrical characteristics of the measuring circuit.

The input signal is preferably a step or pulse-shaped input signal, preferably a digital or substantially rectangular signal, and the corresponding point in time is derived accordingly from an edge of the input signal.

Last but not least, the advantage of the present invention lies in the simplicity of the measuring arrangement. In many control electronics components are already used that can "do" with the signal evaluation according to the invention, so that in the simplest case only an additional component for the sensor Wiring of the sensor is required. This is particularly true when using programmable logic devices (PLD).

A particularly advantageous application of the invention is in the monitoring of servo drives or other drive technologies (e.g. asynchronous machines, brush motors, stepper motors in connection with the respective control electronics, synchronous motors).

Further advantages, features and details of the invention emerge from the following description of preferred exemplary embodiments and with reference to the drawings; these show in:

Figure 1A shows a preferred embodiment of the invention for a circuit with one input and one output.

Figures 1B-1D represent the course of the signals in the circuit of Fig. 1A.

Figure 2 shows a further preferred embodiment of the invention for a circuit with a combined input and output.

The embodiment of the invention shown in FIG. 1 for a switching mode with one input and one output each has a programmable logic module (Programmable Logic Device - PLD) 10 and a measuring circuit 20 coupled to it. In the example according to FIG. 1, the measuring circuit 20 consists of a delay element made of a temperature-dependent resistor 30 and a reference capacitance 40.

In the operating state for determining the temperature at the resistor 30, the PLD 10 either applies a pulse (for a single measurement) or a square wave signal (for a continuous measurement) to the measurement circuit 20, represented in FIG. 1 by an input signal 50. Due to the reference capacitance 40, the measuring circuit 20 has a non-linear electrical characteristic, which results in a signal response 60 to the input signal 50, which is shaped accordingly by the non-linear electrical characteristic is deformed with respect to the input signal 50.

The signal response 60 is received and digitized by the PLD 10, the signal response 60 being sampled with corresponding threshold values, such as an upper and / or a lower threshold value.

FIGS. 1B-1D represent the course of the signals in the circuit according to FIG. 1A. At a time T ₀ , the input signal 50 changes from a low level (here: 0) to a higher level (here: Uo), which is one Jump function corresponds. The voltage at the reference capacitance 40 follows the step function, but with a time delay due to the non-linearity of the reference capacitance 40, the time course of the signal response 60 being known to be determined by the time constant τ formed from the values of the resistor 30 and the capacitance 40. IC shows an example of the course of the signal response 60.

At a time Ti, the value of the signal response 60 reaches a predetermined threshold Uth- Depending on the circuit application of PLD 10 then as an output a digitized above the threshold value U _th output signal as shown in Fig. 1D can indicated output.

Although not explicitly shown in FIGS. 1B-D, it is clear, however, that by providing a further, lower threshold value, the signal response 60 can also be sampled for a negative edge of the input signal 50.

From the time difference .DELTA.t between the times Ti and To together with the ratio of Uh ^to U ₀ the known characteristic of the measuring circuit 20, the instantaneous resistance value of the temperature-dependent resistor 30 and from this the instantaneous temperature value at the resistor 30 can be determined. This can be done, for example, by a corresponding circuitry by the PLD 10.

The accuracy of the measurement can be influenced by the tolerance of the individual components of the measuring circuit 20 and by the threshold value U _{t of} the detection threshold. The accuracy of the circuit can be increased by using a threshold switch with a defined threshold value in the feedback and by using a measuring circuit 20 with individual components with low tolerance.

It is readily apparent and does not require any detailed explanation that any other circuit with a non-linear characteristic can be used instead of the measuring circuit 20 shown in FIG. 1A. The non-linearity can result from the actual sensor 30 (in FIG. 1A: the temperature-dependent resistor 30), its wiring 40 (in FIG. 1A: the reference capacitance 40) and from their combination.

Any electrical component can be used as the sensor 30, the course of which can be used to infer an analogue measurement variable, such as temperature, force, pressure or displacement. In addition to temperature-dependent resistors, capacitors or inductances are particularly suitable for this purpose, in which typically the value of the capacitance / inductance can be varied by the applied force, the pressure or the displacement.

The circuitry 40 can correspond to the type used of the sensor 30 can be adapted to this so as to influence the time profile for the signal response 60. In order to keep the degree of non-linearity of the circuit 40 low, an inductive or capacitive sensor 30 can, for example, be connected to one or more ohmic resistors. Conversely, an ohmic sensor 30, as shown in FIG. 1A, can be connected to a capacitance or inductance.

It is further to be understood that instead of the absolute determination of the measured variable shown above, a relative determination can also be made from the known values of the elements of the circuit 20. For this purpose, the basic characteristic of the circuit 20 must first be known, for example an RC series circuit as shown in FIG. 1A. The signal evaluation can then be calibrated using at least one known value of the measured variable. For example, in FIG. 1A, the time constant τ of the RC series circuit 20 can be determined at a known temperature value and with a known relationship between the resistance value and the temperature of the temperature-dependent resistor 30.

The evaluation effort for the PLD 20 can also be simplified by a suitable choice of the ratio U _h to U ₀ . For example, in the circuit according to FIG. 1A, with a ratio U _th ü ₀ = 0.632, the value of τ = RC results directly from the measured transit time.

Figure 2 shows a further preferred embodiment of the invention for a circuit with a combined input and output. Instead of the 3 connections as in FIG. 1A, only one connection is required for the PLD 10. The measuring element of the temperature-dependent resistor 30 is included connected at one end to the supply voltage and at the other end to the reference capacitance 40. The PLD 10 thereby reaches between the resistor 30 and the capacitance 40, and the capacitance 40 is connected to ground (or another level) with its further end.

In the operating state, the PLD 10 first closes the resistor 30 and the capacitance 40 to ground by defining the connection of the PLD 10 as an output with ground as the output voltage. In this way, the circuit 20 is brought into a defined initial state.

After an adjustable waiting time of the PLD 10, in which the initial state of the temperature-dependent resistor 30 can be ensured, the connection of the PLD 10 is defined as an input, whereby the circuit 20 is activated. Here, too, the time is measured which elapses until the corresponding voltage value of the predetermined threshold (for example U _th ) is present at the connection of the PLD 10. The delay time between the time the circuit 20 is activated and the predetermined threshold is reached is in turn a measure of the measurement variable to be determined. The statements made in relation to FIG. 1A also apply here accordingly.

It can be seen that any other module can be used in place of the PLD 20, which allows the application of a corresponding input signal 50 and an evaluation of the corresponding signal response 60. In the same way, these functions can also be represented by several individual modules or circuits.

Finally, it is understood that the ones used here

Terms such as "principal" or "essential"

Characteristic "based on an idealized behavior of the circuit 20, in which only a minor effect Effects such as stray capacities and the like are neglected.

Claims

Patent claims

1. Device (10, 40) for determining and / or evaluating an analog measured variable, such as preferably temperature,

Force, pressure or path, which acts on an electronic measuring element (30), comprising:

a circuit unit (40) which is coupled to the measuring element (30) to form a measuring circuit (20), the measuring circuit (20) having a non-linear electrical characteristic which is known in its essential characteristics, and

an evaluation unit (10) coupled to the measuring circuit (20) for evaluating a signal response (60) to an input signal (50) applied to the measuring circuit (20), the evaluation unit further comprising:

Means for checking the signal response (60) for reaching a threshold value (U _t h),

Means for determining a running time between reaching the threshold value (U _th ) and a corresponding time ^"

Input signal, and

Means for determining and / or evaluating the analog measured variable from the determined transit time and the essentially known electrical one

Characteristic of the measuring circuit (20).

2. The device (10, 40) according to claim 1, wherein the corresponding point in time of the input signal (50) is determined by an edge of the input signal.

3. The device (10, 40) of claim 1 or 2, wherein the input signal (50) is a digital signal.

4. The device (10, 40) according to any one of claims 1-3, wherein the measuring circuit (20) is an RC circuit or an RL circuit of the first degree.

5. Method for determining and / or evaluating an analog measured variable, such as preferably temperature, force,

Pressure or displacement which acts on an electronic measuring element (30), the measuring element (30) being coupled to a circuit unit (40) for a measuring circuit (20), and the measuring circuit (20) having a non-linear electrical characteristic which is essentially known; with the steps:

(a) Checking a signal response (60) for an input signal (50) acting on the measuring circuit (20) for reaching a

Threshold (Uth),

(b) Determining a running time between reaching the threshold value (Ut _h ) and a corresponding point in time of

Input signal, and

(c) Determination and / or evaluation of the analog measured variable from the determined transit time and the essentially known electrical one

Characteristic of the measuring circuit (20).

6. Device (10, 20) for determining and / or evaluating an analog measured variable, such as preferably temperature, force, pressure or displacement, comprising: an electronic measuring element (30) on which the measured variable acts,

a circuit unit (40) which is coupled to the measuring element (30) to form a measuring circuit (20), the measuring circuit (20) having a non-linear electrical characteristic which is known in its essential characteristics,

a signal unit (10) for applying an input signal (50) to the measuring circuit (20), and

an evaluation unit (10) coupled to the measuring circuit (20) for evaluating a signal response (60) to the input signal (50) from the signal unit (10), the evaluation unit further comprising:

a comparator to compare the

Signal response (60) with a threshold (U _th ) _r

Means for determining a running time between reaching the threshold value (U _t h) and a corresponding time of the

Input signal, and

Characteristic of the measuring circuit (20).

7. The device (10, 20) according to claim 6, wherein the

Input signal (50) is a step or pulse-shaped input signal (50), preferably a digital or in Essentially rectangular signal, and the corresponding point in time is derived from an edge of the input signal.