电池电压低于5V 时，电压量程按钮开关应打在5V档上。
When battery voltage is less than 5V, voltage range switch should be set to 5V.
本电参数测试仪通过AT 89 C 51单片机作为核心的控制元件，由模拟开关hcf 4051构成自动量程数字万用表。
Abstrct: the electrical parameters Tester through AT89C51 SCM as a core element of control by the analog switch HCF4051 constitute a range digital multimeter.
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