The Research Of Measurement Grounding Dc Resistance

The resistance of electrical power's grounding is too low to be measured by normal ohmmeter, and this thesis is an solution of the limitation. SCM, A/D technology and CAD are applied in the design of the multimeasurement grounding resistance dc ohmmeter, which has been purchased as a necessary unit by the electrical power department.First of all, in the thesis, there are the detail introduction of multimeasurement grounding resistance dc ohmmeter's basic fundamentals and the requirements of the functions to achieve. Then, base on the functions to achieve, the design scheme is made. After the contrast of main components, the types of SCM, ADC, embedded micro printer, LCD, DC power and button system are confirmed. Through the study of the components, the circuit expected is finally completed.In the thesis, the detailed introductions are made, include the measurement circuits of standard resistance and measured resistance, power circuit, ADC circuit, -5v power supply circuit, SCM circuit and button circuit.The grounding resistance measurement's principle: 35A invariable current is supplied as measurement current. High power standard resistor is measuring basis. Under the control of the SCM, the analog voltage values of grounding and standard resistor are measured. The values are sent to the SCM for processing via ADC. The average of the multimeasurement is used to reduce the measurement errors. Base on OHM LOW, the value of the grounding resistent is calculated. The result of the value can be displayed in the LCD. If the result typing is needed, micro printer can finish this job.