Time Constant Of Thermocouple Research Articles

On-line dynamic gas pyrometry using two-thermocouple probe

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.

Determination of the Time Constant of Fine-Wire Thermocouples for Compensated Temperature Measurements in Premixed Turbulent Flames

Abstract A new method for the determination of thermocouple time constants is described, which reproduces the large temperature differences between the thermocouple junction and ambient fluid that occur in premixed turbulent flame applications. Time constants measured while the thermocouple is both heating and cooling, as well as the dependency of the time constant on velocity and temperature, are reported. Velocities are varied from 0.6 to 5.5 ms-1, and junction temperatures range from 700K to ISOOK while heating and from 400K to llooK while cooling. Temperature differences between the thermocouple junction and ambient fluid up to 800K are achieved. Radiation losses from the junction are accounted for. Predicted time constants based on commonly used correlations for heat transfer from a cylinder in cross-flow are compared to the data, and it is suggested that free molecular flow effects are partially responsible for the systematic deviation of the data from the theoretical predictions.

Effect of thermocouple sensor dynamics on surface heat flux predictions obtained via inverse heat transfer analysis

A simple thermocouple model is used in this paper to generate data by simulating the imposition of a triangular heat flux history on a one-dimensional domain. A general inverse heat conduction (IHC) analysis computer program is developed and used to estimate the heat flux history based on the generated data. The results show that the effect of the thermocouple's time constant is to diminish the magnitude of the predicted heat flux history and displace its distribution in time.

ARMA models in the analysis of temperature noise measurements in a Super-Phenix subassembly mock-up

The noise analysis methods play an important role in the early, reliable detection of local cooling disturbances in a fast reactor subassembly such as sodium boiling or blockage, which are considered among the initiating events of major disruptive core accidents. In this paper we apply the Box and Jenkins auto-regressive moving-average ARMA models to the analysis of several temperature time-series measured by the Commissariat à l'Energie Atomique in the course of the CFNa experiment carried out at the nuclear center of Grenoble. The source of data is a thermocouple placed at the outlet of a Super-Phenix subassembly mock-up. The analysis shows that a simple ARMA (3,2) model adequately accounts for the observed fluctuations. This model provides methods for a continuous, in situ estimate of the thermocouple time constant, for the identification of a suitable boiling and blockage indicator and for the detection in real time of suddenly occurring disturbances.

Simultaneous Measurement of Fluctuating Temperature and Velocity in a Combustion Field

A velocimeter constructed is composed of detectors and analog computing circuits through which the signals from detectors are directly converted to necessary values. The detectors have a thermocouple, static-and total-pressure probes respectively connected to condenser microphones and a differential pressure meter. With this constitution this velocimeter revealed its performance to be in the same level as a hot-wire velocimeter for a flameless field and provided more accurate turbulence degree in a combustion field than the earlier methods based on the measurement of only pressure variation. Through the application for an open diffusion flame, it was shown that the time constant of thermocouple can be estimated from Nusselt's number equation by Ahmad in combination with the signals obtained, and further that the correlation between temperature and velocity fluctuations becomes negative at the inside of maximum temperature location and positive at its outside.

Thermocouple time constant measurement by cross power spectra

A method of measuring thermocouple time constants is outlined which requires Fourier signal processing. In this method, two thermocouples of differing time constants are placed in a gas flow as closely as possible to one another, and the time constant of the first thermocouple is determined directly from the extremum of the imaginary part of the ratio of the ensemble averaged cross-power spectrum to the ensemble averaged auto-power spectrum of that thermocouple. A coherence function is given for assuring the quality of the data, and results are presented for an experimental test of the method. Some problems with the method are briefly noted.