A high temperature sensor allowing for accurate measurement including wires running through an oxygen ion conductor and connecting to electrodes sandwiching an oxygen ion conductor substrate having an electrical resistance far smaller than the combined resistance (Rpvs) appearing across the lead wires, where Rpvs is determined by way of a pulse voltage sensing method applied across the electrodes. In the case of a two cavity sensor for NOx measurement, Rpvs is not less than 2.6 times greater, or more preferably 4 times greater than the resistance of the wires. In another embodiment, a common internal oxygen reference source cavity is formed inside the oxygen ion conductor so as to provide the same oxygen partial pressure base for other cavities.