Development Of Data Acquisition And Process Software For Multi-channel Thermal Conductivity Meter

Submarine geothermal research is critical to the comprehensive evaluation of the marine oil and gas resources. Combing with the knowledge of the basin evolution, it can help us to understand the temperature history of hydrocarbon source beds, even the organic matter mature history, which is important to the exploration of the marine oil and nature gas. Submarine geothermal research is also important for the accurate evaluation and prediction of the natural gas hydrate resources. It consists of the measurement and calculation of the submarine temperature, the sediment thermal conductivity and the geothermal gradient, et al.There are two kinds of test methods for sediment thermal conductivity, the first one is in-situ measurement, the other one is Indoor measurement. In the former measuring process, marine operation is required, which is very difficult and the equipment is easy to wear and tear; the latter is done in the laboratory, which could reduce the time for maritime operations and the risk of damaging the equipment. After the comparison of these two methods, two ways of measuring the thermal conductivity was almost the same. However, at this stage, the time of thermal conductivity test time is long and inefficient high-precision measurement equipments dependence on imports. Therefore, it is necessary for development of highly efficiency and precision equipment for measuring thermal conductivity. This paper is focuses on the software development of equipment.Choosing a suitable theoretical model, which is the basis of this measurement system, is very critical. In wide ranges of approaches for measuring thermal conductivity, line source method which is one kind of unsteady method is selected in this paper. In practice, there are several measurement models:Pulse Infinite Line Method, dual-probe heat-pulse measurement theory, single-probe continued heating method. The theory of single-probe continued heating method is used in the equipment's design because it is simple & high efficiency.Based on the theory, multi-channel thermal conductivity meter, which is mainly composed of four parts, is designed. It's composed of PC, one-chip computer module, Agilent 34411 and measuring probe (packaged heating wire and thermistor). PC is employed in measurement controlling, data processing and analysis of results. One-chip computer module is employed in analysis of host computer (PC) commands, excitation current, switching channels. Agilent 34411 is employed in data acquisition.Software developed in Visual C++6.0 platform is divided into two parts:the measuring software & evaluation software. The former is employed in controlling measuring process, data acquisition, data calculation and processing. The later is employed in result analysis. Measuring software has several modules:measurement parameter setting module, detection module, data acquisition modules, data processing and save module, and so on. Evaluation software has been divided into analysis for each measurement modules & analysis for single measurements module.Human-computer interaction, which has been designed to be not only aesthetic but also user-friendly, plays an important role in the software. In the measuring software, it is convenient for user to control measurement and observe the situation of measurement, such as the drift, real-time temperature curve in the heating process. In the evaluation software, point-like diagram, histogram and other forms is used; it can be easily to compare the results of the measurements.Data acquisition was mainly achieved by Agilent 34411A digital multimeter, which uses USB to communication with the PC and IVI instrument drivers is supported. Therefore, it is easily to use multimeter.Data processing and evaluation is a key part of the software system. In accordance with design requirements, the resistance value gathered by multimeter must be converted into temperature value by suitable algorithm. Curve fitting ("Steinhart-Hart" formula) and interpolation are used in this paper on account of their own advantages and disadvantages.The measuring principle is based on heating a cylindrical source with infinite length, finite radius, and infinite thermal conductivity in a homogeneous and isotropic sample full space with constant heating power for a finite measuring time. Thermal conductivity then is determined from the temperature rise in the source. In practice, the correct choice of the time interval is difficult. In the early stage of heating the source temperature is strongly affected by the contact resistance between source and full space (not accounted for in the simple approximation used).In the later stages of heating, the influence of boundary effects caused by the actually finite length of the line source (assumed infinite in the theory) increases. Inbetween is a time interval in which the source temperature is dominated by the thermal conductivity of the full space and which should be used for the calculation. It is important to choose a method to examine different time intervals for their suitability for thermal conductivity determination. Then the SAM method is selected because it ensures that only results of physical significance are considered. Then the evaluation module uses the data processed by the algorithm. This enables the user to assess the measurement quality and the reliability of the obtained thermal conductivity values.All the above, the work laid a foundation for further researches.