On-line dynamic gas pyrometry using two-thermocouple probe

Abstract

Real-time observation of the fluctuations in the temperature of a flowing gas may be obtained with a probe containing two geometrically similar thermocouples differing only in size, and an electronic analog circuit using commercially available integrated circuits. The thermocouple lag time constants may vary as gas flow rate varies, and need not be known. Only the thermocouple time-constant ratio, a substantially invariant function of geometry, needs to be known. Under favorable circumstances, even this ratio need not be known in advance and can be determined in situ. The improvement in frequency response depends on the magnitude of the temperature fluctuation and is limited by the quality of the electronics. The system is useful when the thermocouple time constants vary appreciably during the course of the temperature fluctuations because of correlative fluctuations in gas flow rate. A thermocouple simulator is used to adjust the analog circuit and to test its efficacy.

Application of the Deconvolution Methods for Processing of Measurement Signals in the Fast Processes

“…Among several approaches to assessing the relationship of the time constants two basic assumptions were used: (1) the time constant is a function of the size of thermocouple based on empirical equations for the heat transfer coefficient of thin wires [15]; (2) the ratio of the time constants is defined as the ratio of the temperature derivatives, which is valid at equal temperatures of both thermocouples [16,17]. The validity of such approaches in high-enthalpy flow and combustion remains uncertain, as the thermophysical properties can be changed in accordance with the conditions in the high-temperature region.…”