0 William Green December 13, 2016 23:34 AC Ammeters require an external shunt. You have to know the required shunt. The output of the shunt is usually 50mV or 100mV at full scale. I couldn't find much information on this one, but www.risesun.com.tw listed it as ±1.5% FS, 50mV. If it uses a 150A/50mV shunt, you need to disconnect the meter from the shunt and input the required mV (10/30/50mV?) to the meter to record the 50, 100 & 150A readings on the meter. You should also test the shunt too.