Knowledge of the air pressure, temperature and humidity are required for solution of the tank fire control algorithms. The severe environment of the tank makes the use of conventional sensing techniques very difficult. The transmission efficiency of an ultrasonic signal is shown to be directly dependent upon the absolute air pressure and inversely proportional to the absolute temperature. The speed of sound is also proportional to the absolute air temperature and by measuring both the received signal level and time delay, both the temperature and pressure can be derived. By proper choice of the ultrasonic frequency, the ultrasonic loss is also affected by moisture content in the air. The use of two ultrasonic frequencies can then also determine humidity levels.
