Development Of A Geophone Tester Based On The Step-release-method

Geophone(sensor) is the forefront of the seismic exploration system, which is responsible for converting the vibration signal into electrical signal. The signal converted will be recorded by the subsequent seismograph. Geophones are very important parts in the seismic exploration, whose performance affects the quality of the seismic data and the effect of the seismic exploration. Moving-coil-type geophone is one kind of the geophones, whose high ratio of cost to performance, the lower noise and very ruggedness make it become the most popular sensor in seismic exploration. Thousands of geophones should be tested before the large-scale sismic exploration. What’s more, the phones should also be calibrated when they are stored monthly or yearly. Thus, the devolopment of the geophone tester is of much importance.The natural frequency, damping and sensitivity are the most important parameters of the geophone. Different parameters reflect different performance. The geophone tester is used to determine the papameters of the phone and the ability to be used in the sismic exploration.Now, the geophone testers used by the geophyical reserchers are mostly based on the step-release-method. Those parameters are determined directly from the transient response when a step of current is released from the coil of the geophone by the method. However, there is no standard for the amplitude of the exciting current when using this method to calibrate the geophones now. The error of some testers is large for the reason that the designers do not take the selection of the amplitude of the excitiong current into account.The reserchers who want to develop their own geophone testers will meet with many obstacles for the selection of the exciting current, which will influence the effectiveness and pcoceding of the devolopment.In order to make the standard for the current clear when determining the parameters of the geophone, this paper analyzes it theoretical and performs many experiments. Firstly, we introduce that the exciting current will influence the output of geophone theoretical and it is deployed by the actual experiments. Secondly, we select different amplitude of the current to excite the geophones and obtain different testing results. We get the standard of selection of the current finally through comparing the different testing results. The standard we get is of great use to develop the geophone tester.We design our own geophone tester based on the embedded ARM-Linux, according to the testing principles of the parameters. The system is composed of the signal generating circuit, the recording channel, the ARM control circuit, the CF card storage circuit and the touching screen which is used for human-computer interaction. What’s more, we design different testing programs according to different papameters.In the experiments, we test the CDJ-Z60 geophone by our own tester and compare the results with the parameters given by the manufacture. The testing results show that our own instrument has a good performace in the mass. In order to further verify the testing accuracy, we use the LCR tester and the highly precise shaker platform with the laser interferometer to calibrate the geophones, we compare the results obtained by our own geophone tester with them getted by the LCR and the shaker platform to evaluate the accuracy of our instrument. The verification experiment shows that the geophone tester designed has a high accuracy, and it can obtain the damping, natural frequency, sensitivity, distortion, resistence, leakage, noise and the politary of the geophone precisely. What’s more, the geophone tester is able to be used to calibrate the geophones in the yeild or the labrotary for the advantages such as the high ratio of cost to performance, easily operation and so on.