Patent ID: 6300754
Filing Date: 2001-10-09
Classification: G01N

Abstract:
A circuit for a measurement sensor that registers an NOx concentration in a gas, the measurement sensor having an external electrode to be exposed to the gas to be measured, measurement cells including a first measurement cell and a second measurement cell connected to the first measurement cell, a measurement electrode disposed in the second measurement cell, a reference electrode exposed to ambient air, a solid-state electrolyte having the measurement cells disposed therein and the measurement electrode and the reference electrode making contact with the solid-state electrolyte, the circuit comprising:a first circuit configuration for establishing in the first measurement cell an oxygen concentration differing from an oxygen concentration in the gas to be measured;a second circuit configuration for establishing in the second measurement cell an oxygen concentration differing from the oxygen concentration in the first measurement cell; anda third circuit configuration for pumping oxygen ions formed from NOx out of the second measurement cell from the measurement electrode to the external electrode in a pump current, said third circuit configuration including:a controller connected to the measurement electrode and the reference electrode and generating a setting voltage; anda voltage-controlled current source for driving the pump current and receiving the setting voltage generated by said controller, said controller tapping off a Nernst voltage between the measurement electrode and the reference electrode and regulating the setting voltage such that a predicted Nernst voltage is established, a value of the setting voltage being a measure of the pump current and consequently of the NOx concentration to be measured.