New high-precision digital voltmeter, with upper and lower limit voltage alarm output function. Can be used as overvoltage,undervoltage alarm output. If connect with relay it also can be used as overvoltage or undervoltage protection.   3-wires, and you can change it to 2-wires.  Input with anti-reverse protection When the measured voltage below 10V, automatic transfer decimal point,increase the resolution of low voltage.   Featrures:       Measuring range: DC 10V 20V 50V 100V 300V 1000V   Upper and lower limit setting range : 0-10V 20V 50V 100V (0.1V onwards)                                                                0-300V/1000V (1V onwards)   Upper and lower limit output level mode: In the setting range is high level, exceeding the set value is low level.   Minimum resolution: 10V range 0.01V   20V range 0.02V   50V range 0.05V   100V range 0.1V   300V range 0.3V   999V Range 1V   Refresh rate: 300mS / times Display color: Red Operating temperature: -40°C to +85 °C Input reverse polarity protection: yes Wiring: wire-type (Default is 3-wire. If you need to change to 2-wire,please R1 shorted connection{look at the pictures}). Note: when work in 2-wire mode, the measurement range and power supply range is the same, so do not exceed 30V measurements. Measuring the voltage exceeds 30V, use 3-wire. Install method: 2 pieces 2mm screws   Size: 29*23*10 mm (L*W*H)