a pulping digester contains a liquid digesting medium and wood chips dispersed in the medium . the level of the wood chips in the digester is normally below the top of the digester . as chips and digesting medium are fed to the digester and as pulp and digesting medium are withdrawn from the digester , the chip level will vary dependent upon the net addition of chips and withdrawal of pulp . the variable location of the chip level , or chip height , is determined by positioning a temperature sensing means in the upper portion of the digester above the normally desired chip level . the temperature sensed by the sensing means is displayed to and monitored by the digester operator . as the chip level rises toward the temperature sensor , the sensed temperature will fall until the chip level rises above the location of the temperature sensor , after which the sensed temerature will rapidly increase as the chip level continues to rise above the location of the sensing means . the inverse relationship is true as the chip level falls , providing a characteristic curve of temperature versus chip level from which the chip height can be determined .