Sensor apparatus and sensor unit

A sensor apparatus which calculates a concentration of a particular gas contained in a gas under measurement using a gas sensor which includes a sensor element and a heater for heating the sensor element, the sensor element including at least one cell having a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body,

• the sensor apparatus comprising:
• a controller area network (CAN) interface circuit configured to communicate with an engine electronic control unit (ECU);
• a control circuit;
• a microcomputer configured to communicate with the CAN interface circuit and the control circuit;
• and
• connection terminals configured to communicate with the sensor element and the control circuit;
• the microcomputer configured to:
• repeatedly obtain resistance information representing an internal resistance value of the solid electrolyte body to thereby obtain a plurality of the internal resistance values comprising a latest obtained internal resistance value and one or more prior obtained internal resistance values and current information representing a concentration detection current value which flows between the pair of electrodes and whose value varies with the concentration of the particular gas;
• and
• correct a latest obtained concentration detection current value, based on the latest obtained internal resistance value, a target internal resistance value, and a resistance change rate,
• wherein the target internal resistance value is an internal resistance of the solid electrolyte body corresponding to a target temperature at which the solid electrolyte body is maintained by means of heating by the heater so as to enable the sensor element to detect the concentration of the particular gas,
• wherein the resistance change rate is an amount of change in internal resistance per unit time and is calculated based on the plurality of the internal resistance values,
• wherein the microcomputer is configured to correct the value of the latest obtained concentration detection current in accordance with the following equation (2):
• Ipo
• =
• Ip
• -
• α
• ×
• Δ
• ⁢
• Rpvs
• -
• β
• ⁢
• dRpvs
• dt
• (
• 2
• )
• wherein Ip represents the value of the latest obtained concentration detection current represented by the current information, ΔRpvs represents a difference obtained by subtracting the target internal resistance value from the value of the latest obtained internal resistance represented by the resistance information, dRpvs/dt represents the resistance change rate, Ipo represents the corrected value of the concentration detection current, and α and β represent coefficients set in advance as constants.