Method for precisely detecting a signal for example of a sensor
A method for precise acquisition of a signal of a sensor, by an evaluation and control unit which has a multiplexer at whose inputs there is at least one reference voltage whose voltage value is known, a ground potential of the reference voltage, a measurement signal of the exhaust gas sensor, and a ground potential of the measurement signal. A computer is connected downstream from the multiplexer via a transmission path and via an ADC that converts a voltage between its two inputs into a digital value. The method provides that a plurality of individual measurements are carried out in which switching states of the multiplexer are modified, and digital values are subsequently acquired at the output of the ADC. The computer calculates a measurement value, corrected with regard to offset and gain, from these digital values.
1. A method for the precise acquisition of a signal of a sensor by an evaluation and control unit electrically connected to the sensor, the evaluation and control unit having a multiplexer at whose inputs there is at least one reference voltage whose voltage value is known, a ground potential of the reference voltage, a measurement signal of an exhaust gas sensor, and a ground potential of the measurement signal, a computer being connected downstream from the multiplexer via a transmission path and via an analog to digital converter (ADC) that converts a voltage between two inputs of the ADC into a digital value, the method comprising the following steps:
carrying out a plurality of individual measurements, wherein in each of the individual measurements, switching states of the multiplexer are modified, and in each of the individual measurements which digital values are subsequently acquired at an output of the ADC; and
calculating, by the computer, a corrected measurement value, corrected with regard to offset and gain, from the digital values;
wherein the digital values are each acquired before two levels at the inputs of the ADC have settled, or the analog to digital conversion by the ADC is begun before the two levels at the inputs of the ADC have settled,
wherein the two levels at the inputs of the ADC are not considered settled until the output of the ADC achieves at least 86% of a change according to a stationary solution with the modified switching states of the multiplexer.
2. A method for the precise acquisition of a signal of a sensor by an evaluation and control unit electrically connected to the sensor, the evaluation and control unit having a multiplexer at whose inputs there is at least one reference voltage whose voltage value is known, a ground potential of the reference voltage, a measurement signal of an exhaust gas sensor, and a ground potential of the measurement signal, a computer being connected downstream from the multiplexer via a transmission path and via an analog to digital converter (ADC) that converts a voltage between two inputs of the ADC into a digital value, the method comprising the following steps:
carrying out a plurality of individual measurements, wherein in each of the individual measurements, switching states of the multiplexer are modified, and in each of the individual measurements which digital values are subsequently acquired at an output of the ADC; and
calculating, by the computer, a corrected measurement value, corrected with regard to offset and gain, from the digital values;
wherein the digital values are each acquired before two levels at the inputs of the ADC have settled, or the analog to digital conversion by the ADC is begun before the two levels at the inputs of the ADC have settled,
wherein the two levels at the inputs of the ADC are not considered settled until the output of the ADC achieves at least 86% of a change according to a stationary solution with the modified switching states of the multiplexer,
wherein the carrying out step, the following individual measurements are carried out:
a) a reference voltage measurement in which the multiplexer connects the reference voltage to a first input of the two inputs of the ADC and connects the ground potential of the reference voltage to a second input of the two inputs of the ADC, and a reference voltage value is ascertained at the output of the ADC,
b) a reference offset voltage measurement in which the multiplexer connects the ground potential of the reference voltage both inputs of the two inputs of the ADC, and a reference offset voltage value is ascertained at the output of the ADC,
c) a measurement voltage measurement in which the multiplexer connects a measurement voltage of the measurement signal to the first input of the ADC and connects the ground potential of the measurement signal to the second input of the ADC and a measurement voltage value is ascertained at the output of the ADC;
d) a measurement offset voltage measurement in which the multiplexer connects the ground potential of the measurement signal to both inputs of the two inputs of the ADC and a measurement offset voltage value is ascertained at the output of the ADC;
wherein the corrected measurement value U_MuC corrected with regard to offset and gain is calculated according to the following equation:
U_MuC=U Ref *(Z_UM−Z_UMoffset)/(Z_UR−Z_URoffset),
where
U_MuC is the corrected measurement value corrected with regard to offset and gain;
U Ref is the known voltage value of the reference voltage;
Z_UM is the measurement voltage value;
Z_UMoffset is the measurement offset voltage value;
Z_UR is the reference voltage value;
Z_URoffset is the reference offset voltage value.
3. The method as recited in claim 2 , wherein the evaluation and control unit is brought into an identical initial state before each of the individual measurements.
4. The method as recited in claim 2 , wherein the individual measurements have identical timing relative to one another.
5. The method as recited in claim 2 , wherein switches of the multiplexer match one another.
6. The method as recited in claim 1 , wherein the individual measurements and the calculation of the corrected measurement value corrected with regard to offset and gain are cyclically repeated.
7. The method as recited in claim 1 , wherein the sensor is a broadband lambda sensor and the evaluation and control unit is an ASIC.