但同时，这种短路保护带有局限性，在线缆、熔断器和断路器的测试时，会由于电源的主动保护而无法进行。为解决此问题，全天科技可编程直流电源引入低压模式，可正常进行线缆、熔断器和断路器测试，如线缆内阻、熔断器熔断时间。设置方式：按下前面板[Menu]键，进入主界面，选择2.OUTPUTSETTING；选择5.ADVANCEDFUNC，进入高级功能菜单；选择3.SHORTMODE，进入低压模式的设置；该项默认的设置为ON，若用户有线缆或者断路器测试的需求，将此选项设定为OFF后便可正常进行。
PV023R1K1T1NHCC
PV023R1K1T1VMMC
PV023R1K1T1WMRC
PV023R9K1T1NFWS
PV023R1K1JHNMMC
PV023R1K4T1NFHS
PV023R1L1T1NMMC
PV023R1K8T1VMMC
PV023R1K1T1NFRZ
PV023R9K1T1NMMC
PV023R1K4T1NMR1
PV023R1K1T1VFDS
PV023R1K8T1NMMC
PV023R1K8T1NFWS
PV023R1K1T1WMR1
PV023R1K8T1N001
PV023L1K1T1NMMC
PV023R1K4T1NMMC
PV023R1K1T1NKLC
PV023R1K4T1NFR1
PV023R1K1S1NFWS
PV023R1K1T1NFFC
PV023L1K1T1NFWS
PV023R1K1T1WFDS
PV023R1K1T1NFFP
PV023R1L1T1NF
PV023R1K1T1WMM1
PV023R1K1T1NHLC
PV023R1K1T1NMRZ
PV023R1K1T1NMRK
PV023R1K1T1WMMC
PV023R1K1T1NFF1
PV028R1K1T1N001
PV028R1K1T1N100
PV028R1K1T1NFDS
PV028R1K1T1NFR1
PV028R1K1T1NFHS
PV028R1K1T1NMMC
PV028R1K1T1NMM1
PV028R1K1T1NMRC
PV028R1K1T1NFWS
PV028R1K1T1NFRC
PV028R1K1T1NFF1
PV028R1K1T1WMM1
PV028R1K1T1WFR1
PV028R1K8T1NFWS
PV028R1K4T1NFR1
PV028R1K1T1VMMC
PV028R1K1T1NHCC
PV028R1K4T1NMMC
PV028R1K1T1NELC
PV028R1K1T1NHLC
PV028R1K8T1N001
PV028R1K1T1NF
PV028R9K1T1NFWS
PV028R9K1T1NMMC
PV028R1K1T1VFDS
PV028R1K1AYNMRZ
PV028R1K8T1NMMC
PV028R1K1T1NMRK
PV028R1K1T1NFFP
PV028L1K1T1NMMC
PV028R1K1T1NFRZ
PV028R1K1S1NFWS
PV028R1K1T1NMMZ
PV028R1K1T1NMR1
PV028R1K1T1NMFC
PV028R1K1T1WFDS
PV028L1K1T1NFWS
PV028R1K1JHNMMC
PV028R1K1T1NMRZ
PV028R1K4T1NFHS
PV028R1K1T1NMF1
PV028R1K1T1NGLC
PV028R1K1T1WMRC
PV028R1L1T1NMMC
PV028R1K1T1WMMC
PV028R1K1T1WMR1
PV028R1K8T1VMMC
PV028R1K1T1NFFC
PV028R1K1T1NMMK
PV028R1K4T1NMR1
PV032R1K1T1N001
PV032R1K1T1N100
PV032R1K1T1NFDS
PV032R1K1T1NFR1
PV032R1K1T1NFHS
PV032R1K1T1NMMC
PV032R1K1T1NMM1
PV032R1K1T1NMRC
PV032R1K1T1NFWS
PV032R1K1T1NFRC
PV032R1K1T1NFF1
PV032R1K1AYNMTZ
PV032R1K1T1NMFC
PV032R1K1T1NMR1
PV032R1K1T1NMF1
PV032R1K1T1NMRK
PV032R1K1T1NFFP
PV032R1K1T1WMMC
PV032R1K4T1NMMC
PV032R1K8T1VMMC
PV032R1K1T1WFR1
PV032R1K1T1NFFC
PV032R1K1JHNMMC
PV032R1K1T1WMRC
PV032R9K1T1NFWS
但是VVVF缺点是输入功率因数比较低，谐波电流大，直流电路需要大的储能电容。变频器的主回路构成：电源输入—整流桥—启动电阻—母线电容—制动单元（制动电阻）—逆变桥—电源输出。主电路是给异步电动机提供调压调频电源的电力变换部分，它由三部分构成：整流电路：将工频电源转变为直流；平波回路：吸收在变流器和逆变器产生的电压脉动；逆变电路：将直流转变为频率可调的交流电。主要参数测量对与其工作系统主要是由变频器和变频电机两部分组成。
