ARRANGEMENT AND METHOD FOR MEASURING AND CONTROLLING THE HEATING TEMPERATURE IN A SEMICONDUCTOR GAS SENSOR
An arrangement is provided for controlling the heating temperature in a semiconductor gas sensor comprising a control loop, consisting of a heating resistor as automatic control system of a measurement device measuring a physical quantity representing the temperature of the heating resistor, and an actuating unit controlling a power supply of the heating resistor, and a method which utilizes the arrangement. The actuating unit includes a pulsating voltage source, having a first pulse duration, during which the heating resistor is connected to an operating voltage, and a second pulse duration, during which the heating resistor is separated from the operating voltage, whose first and/or second pulse duration can be controlled as a correcting variable, A constant current source applies a measuring current to the heating resistor during the second pulse duration and a measurement device measures the measurement voltage drop across the heating resistor, whose output is designed as a controlled variable feedback in the control loop.
1 . An arrangement for controlling a heating temperature in a semiconductor gas sensor comprising a control loop, including a heating resistor as an automatic control system of a measurement device measuring a physical quantity representing temperature of the heating resistor, and an actuating unit controlling a power supply of the heating resistor, wherein the actuating unit comprises a pulsating voltage source, having a first pulse duration, during which the heating resistor is connected to an operating voltage VDD, and a second pulse duration, during which the heating resistor is separated from the operating voltage VDD, whose first and/or second pulse duration can be controlled as a correcting variable , and further comprising a constant current source applying a measuring current to the heating resistor during the second pulse duration and a measurement device measuring a measurement voltage drop across the heating resistor due to the measurement current, whose output comprises a controlled variable feedback in the control loop.
2 . The arrangement for controlling the heating temperature in a semiconductor gas sensor according to claim 1 , wherein the actuating unit is digitally switchable.
3 . The arrangement for controlling the heating temperature in a semiconductor gas sensor according to claim 1 , wherein a differential amplifier is configured in the control loop for determining a control deviation between the controlled variable feedback and a controlling variable, and a generator and a comparator generate the correcting variable.
4 . A method for measuring and controlling a heating temperature of a heating resistor in a semiconductor gas sensor, utilizing the arrangement according to claim 1 , wherein a physical quantity representing the temperature of the heating resistor constitutes the controlled variable of the control loop, wherein the heating resistor is supplied with a pulsed voltage with a first pulse duration of an on state and a second pulse duration of an off state, wherein the first and/or the second pulse duration constitute the correcting variable of the control loop and the heating resistor receives a measurement current of a constant voltage source during the second pulse duration, wherein a voltage generated by the measurement current across the heating resistor is measured and used as a controlled variable.
5 . The method for measuring and controlling the heating temperature of a heating resistor in a semiconductor gas sensor according to claim 4 , wherein there is a periodic switching between the first and the second switching state by means of an actuating element.
6 . The method for measuring and controlling the heating temperature of a heating resistor in a semiconductor gas sensor according to claim 5 , wherein the voltage across the heating resistor generated by the measurement current is subtracted from a setpoint setting and a deviation is amplified in an amplifier.
7 . The method for measuring and controlling the heating temperature of a heating resistor in a semiconductor gas sensor according to claim 6 , wherein the deviation of the heating temperature and the setpoint setting is compared with a modulation signal by a comparator, and the correcting variable for control of the actuating unit and the measurement circuit is generated from the result of the comparison.
8 . The method for measuring and controlling the heating temperature of a heating resistor in a semiconductor gas sensor according to claim 7 , wherein the correcting variable comprises a PWM signal.
9 . The method for measuring and controlling the heating temperature of a heating resistor in a semiconductor gas sensor according to claim 6 , wherein a duration of the first switching state and a duration of the second switching state form a timing ratio m, and a heat generated in the heating resistor is adjusted in terms of the timing ratio m.