Apparatus for measuring ammonia concentration, system for measuring ammonia concentration, system for treating exhaust gas, and method for measuring ammonia concentration

An apparatus for measuring ammonia concentration in a target gas with a sensor element including a mixed potential cell that includes a solid electrolyte body, a detection electrode arranged on the solid electrolyte body, and a reference electrode arranged on the solid electrolyte body, the apparatus comprising:

• a first detection circuit connected to the detection electrode and the reference electrode, the detection electrode having a detection sensitivity to ammonia concentration in the target gas and establishing a mixed potential depending on the ammonia concentration in the target gas, the first detection circuit measuring an electromotive force (EMF) between the detection electrode and the reference electrode;
• a second detection circuit that measures oxygen concentration in the target gas;
• a processor coupled to the first and second detection circuits and to a memory, the memory storing instructions that when executed configure the processor to:
• acquire information from the first detection circuit about the electromotive force of the mixed potential cell while the detection electrode is exposed to the target gas;
• acquire information from the second detection circuit about oxygen concentration in the target gas;
• derive the ammonia concentration in the target gas based on the acquired information about the electromotive force, the acquired information about the oxygen concentration, and a relationship represented by formula (1):
• EMF=α loga(pNH3)−β logb(pO2)+γ logc(pNH3)×logd(pO2)+B (1)
• (where
• EMF:
• an electromotive force of the mixed potential cell,
• α, β, γ, and B:
• constants (provided that each of α, β, and γ≠0),
• a, b, c, and d:
• any base (provided that each of a, b, c, and d≠1, and each of a, b, c, and d>0),
• pNH3:
• the ammonia concentration in the target gas, and
• pO2:
• the oxygen concentration in the target gas);
• and
• store the derived ammonia concentration in the target gas in the memory.