DE3824671A1 - Method and device for producing at least one signal, which is coded in the time domain, from an analog signal - Google Patents

Abstract

The subject matter of the invention comprises a method and a device for producing at least one signal, which is coded in the time domain and can be transmitted via a bus, from an analog signal. The analog signal is integrated, using an integrator (12), by means of a double-integration process during a first, firmly specified or measured first time. After this, a reference signal with a suitable mathematical sign is integrated using the same integrator until the original state of the integrator (12) at the start of the double integration is reached. Time-marking signals related to the time variables of the integration steps are transmitted successively to an evaluation arrangement (18). <IMAGE>

Description

The invention relates to a method for production at least one bus-transmissible coded in the time domain Signals from an analog signal from a sensor and onto a Device for performing the method.

Electrical transducers, whose output signal time-analog signal can be easily multiplexed. An example of this are temperature sensors with quartz crystals (DE-OS 31 28 706). Their temperature-dependent frequency after appropriate division into a pulse interval signal converted, transmitted over a simple bus and from one Evaluation unit decoded. A corresponding procedure is when using sensor elements, the voltage or bridges supply voltage signals, with the help of simple oscillators circuits possible (electric indicator No. 11 (30), pages 25-27  (1977)), but fails in practice with high accuracy requirements for the drift or the temperature response of the necessary capacitors that help determine the frequency.

The invention has for its object a method of to further develop the genus described above in such a way that the analog signal from the sensor with a converter arrangement largely independent of tolerances and timing Changes in the characteristic values of the components of the converter arrangement converted into at least one time interval signal becomes.

The object is achieved in that with a Double integration process first through the analog signal an integrator during a predetermined or measured first time is integrated that after that Reference signal with a suitable sign with the same Integrator is integrated until the initial state of the Integrators is reached at the beginning of double integration and that on the temporal variables of the integration steps related time stamp signals in succession to an evaluation arrangement be transferred. The time stamp signals can time multiplexed with time stamp signals from other sensors or Converter arrangements are transmitted on the same channel. Therefore, the arrangement is also for connection to a bus, e.g. of a microcomputer. The evaluation arrangement can hence the timestamp signals received by numerous sensors and to process. The values corresponding to the analog signals provides the evaluation arrangement with high accuracy Available.

Preferably at least at the beginning and at the end of the Double integration generates time stamp signals, the temporal Distances of the subsequent time stamp signals to the time  brand signals at the beginning of the double integration of the Evaluation arrangement for the determination of the analog signals corresponding digital values are processed further. The decisive factor is the time interval between those of the same converter arrangement generated time stamp signals. These Time intervals also remain relative during transmission long transmission channels or buses. The procedure is therefore also suitable for sensors in larger Distances are arranged from each other.

In a particularly favorable embodiment, the reference signal T is proportional to the current flowing through the sensor or the supply voltage for an arrangement containing a sensor element for generating an analog signal which corresponds to a physical quantity detected by the sensor. A number of sensors require operating or supply voltages, which are used at least with a proportional portion as reference voltage during the integration by the method described above. The measurement accuracy is not affected by fluctuations in the supply voltage, which cause fluctuations in the analog sensor signals.

It is useful if the first time by one, a precise Time interval generating timer is specified, the Value of the time interval stored in the evaluation arrangement becomes. With this procedure, the transmission of the time stamp is sufficient at the beginning and at the end of the double integration in order to Evaluation arrangement the ratio of the second integration time to to determine the total integration time. The second integration namely time is the difference of the total, by the two Time stamp signals determinable integration time and the saved time. The one between the two time stamp signals the evaluation system e.g. by means of Counting clock pulses measured at constant frequency. The  Formation of the quotient from the first integration period and overall Integration time is for eliminating disruptive influences of importance to the measuring accuracy.

In another cheap embodiment, the first integration time does not specify a precise time element Time stamp signal at the beginning of the double integration, at the end of the first integration period and at the end of double integration generated, with at least the time in the evaluation arrangement between the first and the second time stamp signal as well as the Time between the first and the last time stamp signal is measured. From the two current values, the Evaluation arrangement the quotient.

A device for performing the method exists according to the invention in that in a converter arrangement Integrator via at least a first switching element to the analog signal and via at least one second switching element the reference signal can be applied and that the integrator to a Control logic is connected, which operates the switches and the Time stamp signals generated.

The analog voltage is expediently the output voltage of a thermocouple. It is also advantageous that Bridge diagonal voltage of a bridge circuit as analog Voltage, e.g. in the bridge circuit Strain gauge is arranged. As an analog voltage can also the voltage drop across a temperature measuring resistor be used, the reference voltage on one in series with the temperature measuring resistor arranged reference resistor stand can be tapped.  

A measuring system with several sensors, each with one Transducer arrangement are suitably contains a two-wire line to which the converter arrangements and one Evaluation arrangement are connected, the converter arrangements by addressing signals of the evaluation arrangement for Output of the time stamp signals can be activated. In particular current pulses are used as time stamp signals.

Instead of simple impulses for time stamping Double pulses of defined length with a fixed pulse interval or then encoded pulse groups for the time marking are transmitted when interference pulses are detected and measurement errors should be prevented due to interference.

Further details, advantages and features of the invention arise not only from the claims that these taking features - individually and / or in combination -, but also from the description below of in the Preferred embodiments shown in the drawing.

Show it:

Fig. 1 is a diagram of an arrangement for generating a coded signal in the time domain from the analog signal a bridge diagonal of a bridge circuit containing a sensor,

Fig. 2 is a block diagram of an arrangement for generating an encoded in the time domain signal from an analog signal from a temperature measuring resistor,

Fig. 3 is a timing diagram of the integration of a reference signal and an analog signal in connection with integration dependent generated time mark signals,

Fig. 4 is a circuit diagram of a measuring system with sensors and converter arrangements which are jointly connected to a central evaluation device to a two-wire line,

FIG. 5 shows a time diagram of the addressing signals and generated by the evaluation arrangement according to FIG. 4

Fig. 6 is a timing diagram of the time stamp signals generated by a converter arrangement.

For example, a pressure sensor ( 1 ) contains four resistors ( R 1 ), ( R 2 ), ( R 3 ), ( R 4 ) arranged in a bridge circuit, at least one of which is designed as a strain gauge and can be changed as a function of pressure. The bridge circuit is supplied by a supply voltage, which is designated U _ref . The bridge diagonal voltage labeled U _x , which is a measure of the pressure, is applied to inputs ( 2 ), ( 3 ) of a converter arrangement ( 4 ) which contains further inputs ( 5 ), ( 6 ) to which the supply voltage U _ref is laid. The converter arrangement ( 4 ) has switching elements ( 7 ), ( 8 ) connected to the inputs ( 2 ), ( 3 ), which can be actuated together by a control logic ( 9 ). Switching elements ( 10 ), ( 11 ) are also connected to the inputs ( 5 ), ( 6 ), which can also be operated together by the control logic ( 9 ). The switching elements ( 7 ), ( 8 ) and ( 10 ), ( 11 ) are alternately opened and closed in the integrating mode of operation, ie when the switching elements ( 7 ), ( 8 ) are closed, the switching elements ( 10 ), ( 11 ) are open and vice versa . The switching elements ( 7 ), ( 10 ) are connected together to a resistor R of an integrator ( 12 ). The resistor R is followed by a differential amplifier ( 13 ), the second input of which is connected to the two switching elements ( 8 ), ( 11 ). A capacitor C is arranged between the input and output of the integrator ( 13 ), to which a switching element ( 14 ) which can be actuated by the control logic ( 9 ) is connected in parallel. The output of the differential amplifier ( 13 ) is connected to the control logic ( 9 ), which has a comparator (not shown). The control logic ( 9 ) contains outputs ( 15 ), ( 16 ) which are connected to a two-wire line ( 17 ). An evaluation arrangement ( 18 ) is also connected to the two-wire line ( 17 ).

With the arrangement shown in Fig. 1, the analog signal U _{x of} the bridge diagonal is converted into pulse spacing signals which are transmitted on the two-wire line ( 17 ). With the pulse interval signals, a value is obtained in the evaluation arrangement ( 18 ) which is proportional to the ratio U _x / U _ref and independent of U _ref .

In a first time, the control logic ( 9 ) closes the switches ( 7 ), ( 8 ). During this time, the analog voltage U _{x is} integrated. After the first time, the control logic ( 9 ) opens the switches ( 7 ), ( 8 ) and closes the switches ( 10 ), ( 11 ). During this time, the reference voltage U _{ref is integrated} with the opposite sign (inverted). The comparator in the control logic ( 9 ) determines during the double integration process if the integrated variable has reached the same value as at the beginning of the integration and ends the integration by opening the switches ( 7 ), ( 8 ), ( 10 ), ( 11 ) or by closing the switch ( 14 ). At the beginning of the integration, the control logic ( 9 ) outputs a time stamp signal, for example a pulse, at the outputs ( 15 ), ( 16 ). At the end of the integration, the control logic ( 9 ) outputs a digital time stamp signal, for example a pulse, at the outputs ( 15 ), ( 16 ). If the first time is precisely specified by the control logic, then a corresponding value is stored in the evaluation arrangement ( 18 ). The formation of the ratio U _x / U _ref takes place according to the invention using the method also referred to as the “dual slope” method, which is used in slow analog-digital converters. Such analog-digital converters can be used directly to implement the converter arrangement ( 4 ), provided that they provide the required time stamp signals at an output. In contrast to the digital value desired for AD converters, only time information is transmitted here.

In the arrangement shown in FIG. 2, a temperature measuring resistor R _{x is connected} in series with a reference resistor R _ref to a supply voltage U. The resistors R _x and R _ref are connected to the converter arrangement. The voltage tapped at R _{x is applied} to the inputs ( 2 ), ( 3 ), while the voltage tapped at R _{ref is} fed to the inputs ( 5 ), ( 6 ). The converter arrangement ( 4 ) is connected to the evaluation arrangement ( 18 ) in the same way as in the arrangement shown in FIG. 1. The resistance ratio R _x / R _ref is converted into a pulse spacing ratio in the arrangement shown in FIG. 2. R _x / R _ref = U _x / U _ref applies, the ratio being independent of the supply voltage U.

In Fig. 3, the output voltage of the integrator (12) in function of time t is shown. The double integration starts at a time 0. It is assumed that the analog voltages U _x and U _ref are constant during the duration of the double integration.

As shown in FIG. 3, the voltage U _{x is} first integrated with an integrator ( 12 ) at the beginning of a measuring cycle in the first integration step for a fixed time T ₀, the following equation applying:

U _s (t) denotes the output voltage of the integrator ( 12 ) and T ₀ the first integration time. A time T _x is then determined in a second integration step, which the inverted reference voltage U _ref has to be integrated until the integrator ( 12 ) has reached its initial state again. The following applies:

The following applies:

The time constant RC of the integrator ( 12 ) is not included in the accuracy of the ratio.

If the fixed integration time is realized by a sufficiently precise timing element (e.g. high-quality crystal oscillator) in the converter arrangement ( 4 ), it is sufficient to transmit one time stamp signal ( 19 ) or ( 20 ) at the beginning and at the end of the integration time at a distance T ₀ + T _x . The ratio of U _x / U _ref is then calculated in the evaluation arrangement ( 18 ) by forming the quotient (( T ₀ + T _x ) - T ₀) / T ₀, only T ₀ + T _x and T ₀ being measured is known. The fixed time is determined, for example, by adding up a predetermined number of clock pulses.

The circuit can be simplified by eliminating the influence of an inaccurate timer for the time interval T ₀ by the time stamp signal ( 19 ) at the beginning of the integration phase, a time stamp signal ( 21 ) after the fixed first integration time T ₀ and the time stamp signal ( 20 ) is sent at the end of the integration phase. The two time intervals T ₀ and T _x are then measured directly in the evaluation electronics and the corresponding quotient is formed.

The time stamp signals are shown in FIG. 3 as square-wave signals which are formed by currents i which reach the evaluation arrangement ( 18 ) on the two-wire line ( 17 ).

In FIG. 4, a measuring system is illustrated that a number of sensors S 1, S 2, S 3. . . Contains SN , which are distributed in a process and each output analog output voltages that are characteristic of a physical quantity. Each sensor S 1 , S 2 , S 3 . . . SN is connected to a converter arrangement ( 22 ), ( 23 ), ( 24 ), ( 25 ). The outputs of the converter arrangements ( 22 ), ( 23 ), ( 24 ), ( 25 ) are each connected to a two-wire line ( 27 ), which preferably belongs to a bus that works, for example, in series. A central evaluation arrangement ( 28 ) is connected to the two-wire line ( 27 ).

The converter arrangements ( 22 ) to ( 25 ) differ from the converter arrangement ( 4 ) in that they are addressable, ie they have address decoding devices and downstream elements with which the integrators and the control logic ( 9 ) are put into operation. For addressing, voltage pulses, e.g. B. ( 26 ), ( 29 ) through the evaluation arrangement ( 28 ) on the two-wire line ( 27 ). Counters preset to a certain number can be used as address decoders in the converter arrangements ( 22 ) to ( 25 ). If one of the converter arrangements ( 22 ) to ( 25 ) detects its address, it generates the time marker signals ( 19 ), ( 20 ) or ( 19 ), ( 20 ), ( 21 ) shown in FIG. 3. To distinguish between signal and interference pulses, double pulses with a fixed pulse interval or defined pulse groups can be sent instead of simple pulses. Double pulses ( 30 ), ( 31 ) at time 0, double pulses ( 32 ), ( 33 ) at the end of time T ₀ and double pulses ( 34 ), ( 35 ) at the end of time T ₀ + T _x are shown in FIG. 6 .

Claims (11)

1. A method for generating at least one coded in the time domain, bus-transmissible signal from an analog signal from a sensor, characterized in that with a double integration method, the analog signal is first integrated by an integrator during a predetermined or measured first time, and then a reference signal is integrated with the same integrator until the initial state of the integrator is reached at the beginning of double integration and that digital time stamp signals related to the time variables of the integration steps are successively transmitted to an evaluation arrangement. 2. The method according to claim 1, characterized, that at least at the beginning and at the end of double integration Time stamp signals are generated, the temporal Distances of the following time stamp signals to the Time stamp signals at the beginning of the double integration of the Evaluation arrangement for the determination of the analog Processed signals corresponding to digital values will. 3. The method according to claim 1 or 2, characterized, that the reference signal is flowing through the sensor Current or the supply voltage for a sensor element containing arrangement for generating an analog signal is proportional to a physica detected by the sensor size. 4. Method according to one or more of the preceding Expectations, characterized, that the first time through a precise time interval generating timer is specified, the value of Time interval is stored in the evaluation arrangement. 5. The method according to one or more of claims 1 to 3, characterized, that in the case of one that did not precisely specify the first time Timing element time stamp signals at the beginning of double integration, at the end of the first integration period and at the end of the Double integration are generated, being in the evaluation arrange at least the time between the first and second time stamp signal and the time between the first and last time stamp signal is measured.   6. Device for performing the method according to one or more of the preceding claims, characterized in that in a converter arrangement ( 4 ) an integrator ( 12 ) via at least a first switching element ( 7 , 8 ) to the analog signal and via at least a second switching element ( 10 , 11 ) can be applied to the reference signal and that the integrator ( 12 ) is connected to a control logic ( 9 ) which actuates the switches ( 7 , 8 , 10 , 11 ) and generates the time stamp signals. 7. The device according to claim 6, characterized, that a thermocouple is attached to the converter assembly is closed. 8. The device according to claim 6, characterized in that the bridge voltage of a sensor having a bridge circuit ( 1 ) such as pressure sensor and the supply voltage of the bridge circuit to a converter arrangement ( 4 ) are placed. 9. The device according to claim 6, characterized in that the voltage drops across a temperature measuring resistor ( R _x ) and at a stand arranged in series with the temperature measuring resistor reference resistor ( R _ref ) are placed on a converter arrangement ( 4 ). 10. Measuring system according to one or more of claims 6 to 9 with several sensors, characterized in that each sensor ( S 1 , S 2 , S 3 , SN ) is connected to a converter arrangement ( 22 , 23 , 24 , 25 ), that the converter arrangements ( 22 , 23 , 24 , 25 ) and an evaluation arrangement ( 28 ) are connected together to a two-wire line ( 27 ) and that the converter arrangements ( 22 , 23 , 24 , 25 ) by addressing signals of the evaluation arrangement ( 28 ) for output the time stamp signals can be activated. 11. Measuring system according to claim 10, characterized in that the time stamp signals are double pulses ( 30 , 31 ; 32 , 33 ; 34 , 35 ) with a fixed pulse spacing and a defined length or pulse groups.