Apparatus for measuring a state variable in a gas with at least one semiconductive gas sensor
AssigneeRWE Energie Aktiengesellschaft
InventorsJorg Kelleter, Claus-Dieter Kohl, Heinz Petig
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Abstract
To eliminate the effects of semiconductive sensor aging in the use of a semiconductive sensor for measuring the state variables of a gas in a system in which a pair of electrodes are embedded in an active semiconductive layer so that the conductivity of the semiconductive layer varies as a function of the state variable, a field electrode is provided and superimposed upon the measurement voltage, a voltage pulse is applied intermittently and the characteristic of the resulting current pulse is used to compensate for changes resulting from aging of the sensor.
Claims20
An apparatus for measuring a state variable in a gas, comprising:
- a semiconductive gas sensor disposed in a gas having a state variable to be monitored, said semiconductive gas sensor comprising:
- an insulating layer,
- a field electrode on said insulating layer,
- an active semiconductor layer on said insulating layer and spaced by said insulating layer from said field electrode, and
- two spaced apart further electrodes embedded in said semiconductor layer and isolated from said field electrode;
- a power supply connected in circuit with said further electrodes;
- a measurement-signal processor connected in circuit with said power supply and said further electrodes of said semiconductive gas sensor for detecting a signal across said semiconductive gas sensor representing conductivity of said semiconductive layer and said state variable;
- a voltage-pulse generator connected across said field electrode and at least one of said further electrodes for applying time-spaced measurement pulses between said field electrode and said one of said further electrodes for autogenous control of sensor functioning by generating conductivity changes in said semiconductive layer as a function of time which are measured by said measurement-signal processor for each of said pulses;
- and
- means responsive to the measurement pulses for superimposing upon each of said measurement pulses a respective second measurement signal which is modified by aging of the semiconductive layer.
In a method of measuring a state variable in a gas with an apparatus which comprises:
- a semiconductive gas sensor disposed in a gas having a state variable to be monitored, said semiconductive gas sensor comprising:
- an insulating layer,
- a field electrode on said insulating layer,
- an active semiconductor layer on said insulating layer and spaced by said insulating layer from said field electrode, and
- two spaced apart further electrodes embedded in said semiconductor layer and isolated from said field electrode;
- a power supply connected in circuit with said further electrodes;
- a measurement-signal processor connected in circuit with said power supply and said further electrodes of said semiconductive gas sensor for detecting a signal across said semiconductive gas sensor representing conductivity of said semiconductive layer and said state variable;
- a voltage-pulse generator connected across said field electrode and at least one of said further electrodes for applying time-spaced measurement pulses between said field electrode and said one of said further electrodes for autogenous control of sensor functioning by generating conductivity changes in said semiconductive layer as a function of time which are measured by said measurement-signal processor, the improvement which comprises the steps of:
- generating for each of said measurement pulses a respective second measurement signal,
- superimposing each second measurement signal upon the respective measurement pulse, each second measurement signal being modifiable in response to aging of the semiconductive layer, and
- evaluating a change in a rise time of said second measurement signal for each of said measurement pulses as a function of aging.
Dependencies are inferred from the claim text.