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Current sampling is used in the vast majority of auto lamp test system and the testing and controlling system of other products. It can observe and record the current value in the detection process, with the purpose to judge whether the various features of the products can meet the test standard. Based on the testing demand of mass production, this design devised a smart and multi-channel sampling circuit with pre-correction function, which ensures the stability and accuracy of sampling circuit. This circuit has the characteristics of small volume and good heat dissipation, has a good automatic judgment function (upper and lower limit), and has other functions such as preserving and summarize the record of all test data. Keywords—pre-correction; multi-channel; current sampling I. THE EXISTING PROBLEMS OF CURRENT CIRCUITS In the current sampling circuit, the most common method is to use current transformer or high power sampling resistance. Especially when more channels are need, the cost of using current transformer is too high. However, the volume of high power sampling resistor is big, the calorific power (power consumption) are also relatively large with higher cost. So it is not very appropriate to adopt it in the occasions where multichannel and large volume are required. In this design, constantan wire is used as the current sampling resistance to provide current sampling with small volume and low cost. But in actual design, a new problem is emerging. Due to the shunt characteristics of sampling resistor, the resistance of constantan wire is generally smaller (typically between 0.001 ohms to 1 ohm), especially after welding, the resistance in the welding dish will be a short circuit. The effective lengths of the resistance will be smaller and do not match, which leads to the inaccuracy of the test results. Circuit board is thick, the hole part through which the constantan wire is metalized will be a short circuit, this paragraph of resistance will be smaller. So in the design of sampling resistance using constantan wire, the general engineer can often succeed within a single sample, but when the sampling resistance is mass produced, the result is not stable, and the current sampling values are often found to be biased. Another problem is that the current circuit of the traditional single-chip microcomputer can only real-time display the current sampling value. It is always difficult to record and manage the historical data. II. OVERALL DESIGN According to the demand, this design not only used constantan wire as the sampling resistance, but also uses precorrection circuit and NI data acquisition card to overcome the above problems. The workflow is shown in Figure I, the external current road (n road), through the interface circuit, enters -layout/calibration switch control circuit, and then into -the current sampling circuit, by -multiple selected switch and isolating amplifying circuit, it enters -data acquisition card with time sequence , finally goes to the last data access computer. According to the need, enterprise engineers can achieve all sorts of monitoring, analyzing and recording functions, among which multi-channel switch and input channel selection and control are output by computer through data acquisition card. Layout/ Calibration Switch Control Circuit 1 Produce Circuit of Pre-correction Current 6 Multiple Selected Switch and Isolating Amplifying circuit3 Multi-way Switch Selection Signal D0-D3 Current Sampling Circuit

The Design of Smart and Multi-channel Sampling Circuits with Pre-correction Function