An in situ oxygen analyzer having an intrinsically-safe output and a heated probe is provided. The probe is extendable into a source of process gas and has an oxygen sensor and heater disposed therein. The heater is configured to heat the oxygen sensor to a temperature sufficient to operate the oxygen sensor. A housing is coupled to the probe and has first and second chambers. The first chamber is explosion-rated and includes non-intrinsically safe circuitry coupled to the heater to energize the heater. The second chamber contains only intrinsically-safe circuitry that complies with an intrinsically-safe specification. The first and second chambers are isolated from one another. The non-intrinsically-safe circuitry is coupled to the intrinsically-safe circuitry through an energy-limiting isolator.