Circuit arrangement for the evaluation of a signal produced by a semiconductor gas sensor

• US 4,992,965 A
• Filed: 11/30/1988
• Issued: 02/12/1991
• Est. Priority Date: 04/02/1987
• Status: Expired due to Term

• Current Assignee: Paragon AG
• Original Assignee: Eftag-Entstaubungs- und Fordertechnik AG
• Inventors: Rump, Hanns, Vietze, Helmut, Holter, Heinz
• Primary Examiner(s): Dixon, Joseph L.
• Application Number:
  US07/294,606
• Time in Patent Office: 804 Days
• Field of Search: 364/551.01, 364/424.05, 364/148, 364/497, 236/49.3, 73/23, 73/27, 98/2.01, 98/2.11, 340/628, 340/632, 340/634, 165/16, 165/42
• US Class Current: 701/36
• CPC Class Codes: B60H 1/008 the input being air quality
• CPC Class Codes: B60H 3/0085 Smell or pollution preventing arrangements B60H3/0007, B60H3/0071, B60H3/02, B60H3/06 take precedence
• CPC Class Codes: G01N 27/122 Circuits particularly adapted therefor, e.g. linearising circuits

Abstract

A circuit for the evaluation of a signal produced by a semiconductor gas sensor provides a reliable control for manipulating a recirculated air valve in motor vehicles and their air-conditioning systems and includes a voltage divider connected with an integrator having a time constant bigger than time needed for reaching a peak of noxious gases outside of the motor vehicle.

Claims

1. A gas-sensing system for controlling an air-recirculation valve in a motor vehicle having an interior to which air from outside can be supplied or in which air can be recirculated in accordance with a setting of the air-recirculation valve, said sensing system comprising:

a semiconductor sensor providing an output signal corresponding to a concentration of external noxious gases having a critical high level of the concentration;

an adjustable electricity source connected in series with said sensor and forming therewith a voltage divider;

control means connected with said divider and receiving the output signal for realizing a time delay of said output signal with a time constant higher than a time needed for forming said critical level of said noxious gases and for producing a control signal and feeding the control signal to the source to modify the output signal of the sensor when the time constant is exceeded so as to compensate for a gradual change in concentration exceeding the time delay; and

a comparator receiving said control signal and operatively connected with said voltage divider and with said control means, said comparator processing said control signal and a reference signal corresponding to said critical high level, said comparator switching the air-recirculation valve from an exterior air-supply position to an interior air-recirculation position upon said control signal exceeding said reference signal during a time at least equal to said time constant.

2. The gas-sensing system defined in claim 1 wherein said source is a controlled current or voltage source, said controlling means being connected with said current or voltage source and forming a feedback loop realizing said time delay.

3. The gas-sensing system defined in claim 2 wherein said means for controlling include a resistor-capacitor combination.

4. The gas-sensing system defined in claim 1 wherein said controlling means is a microprocessor provided with an A/D converter and with a binary register, said output signal being digitized and said reference signal being sorted in said microprocessor.

5. The gas-sensing system defined in claim 4 wherein said reference signal is varied with respect to a level of the noxious gases prior to being stored.

6. The gas-sensing system defined in claim 4, further comprising means for heating said sensor, said means for heating including a filament and being connected with said means for controlling, said means for heating receiving another signal from said means for controlling, said other signal being in a form of pulses, a first pulse switching said means for heating and being conveyed for a time period longer than a time period of each of following pulses, said first pulse heating said sensor with a filament power about twice as much as each of said following pulses, said following pulses being identical.

7. The gas-sensing system defined in claim 1 wherein said time constant is varied from a few hours to a few minutes.

8. The gas-sensing system defined in claim 1 wherein said comparator is a switching transistor connected with said controlling means.