The TDEM-TEST system is meant for testing and verification of the Tsikl-type equipment. This system can be also used with other equipment designed for the transient electromagnetic method. The TDEM-TEST system allows the quality and reliability of transient signal measurements to be assessed.
The idea of the TDEM- TEST system is in a physical modeling procedure using a model of geoelectrical medium known as an S-plane. A thin sheet of nonmagnetic metal is used as such a model
The figure presents a general circuit of the system, basic equipment and some measurement results (Stau(t) curves). The Stau(t) transformation is used in the PROBA-software designed for Tsikl-7 primary data processing and as a program item for field data geophysical analysis. It is obtainable as an individual program for the hardware system.
1. The procedure of laboratory testing (modeling) and result processing resembles closely the process of field TEM sounding. The method’s simplicity and visualization are very good for the practical purpose of testing the device. Therefore the System is used to advantage as a training stand for training novice users of the equipment and acquirement of skills in processing and interpretation of measured results.
2. Within the system we adopt such a scale of modeling at which a geophysicist operates on those parameters of the unit with which he often deals in practice. For example, the transmitter coil is taken by default to be 50×50 m; (the actual dimension of the transmitter coil is of 50×50 mm), (the geometrical scale of transition is 1 mm to 1 m). Obtained and used values of longitudinal conductance of medium models are from units to several tens of siemens. (The actual conductance of models is 1 000 times higher). It allows the operator to correlate easily model results with in-situ results. In this case the proper results of test measurements remain the same.
3. And, finally, one of the most interesting features in the analysis of test measurement results. It is known that analog shapers of the test signal (on the basis of inductances, S-planes) depend heavily on the environmental temperature. Test works are carried out both indoor and outdoor often in frosty weather. To compare such measurements is a troublesome matter. In our case the problem of comparison becomes significantly simpler if we analyze not emf of Rotau curves but those of Stau(t) apparent longitudinal conductance. Influenced by temperature, values of the model longitudinal conductance vary over just about 0.4% of grade, but their form remains constant during all transient periods. Let us exemplify our statements. Seen below are emf and Rotau curves (at the top) and Stau(t) curves (at the bottom).
The top curves demonstrate their nonlinear dissimilarities from the temperature. The Stau(t) curves therewith are parallel in their informational part (to be more exact over the whole range of times), and show variations of longitudinal conductance of the model with the temperature. At the actual difference in temperatures of 300 С (used in the given experiment), the predicted change in longitudinal conductance of the model makes up 12%, it is that we observe practically.
Thus, the main conclusion is as follows: if the Stau (t) curve indicates the horizontal position in the sheet (as shown in the figure), then emf values, current magnitude, parameters of the system conform with each other, and their profile represents true measurement results. It means that it is possible to diagnose the test measurement reliability to a considerable extent without comparing theoretical and experimental curves.
Along with the above check relying on the examination of Stau curves users can invoke an easier-to-understand standard check, if they have a program of direct and indirect TNFS problem. The TDEM-TEST system manual available to users give certain model and coil parameters, so one can interpret laboratory measurement results and compare the obtained parameters with those given in the manual or solve the direct problem and compare the obtained curve with the experimental one. In this case you should take into account that experimental data are very sensitive to model temperatures, coil heights and time “delays”. Providing you need such a more in-depth analysis of test measurements, contact the developers. If you have trouble solving the problems, address the developers:
Aleksandr K. Zakharkin, Nataliya N. Tarlo