Resistance Measurement Signal Conditioning Plug-On. The VT1518A 4-wire Resistance Measurement SCP provides four programmable current source channels (with input over-voltage protection) for excitation. Each current source can be programmed to provide either 30 mA or 433 mA. The VT1518A also has four channels of analog input with x16 gain and 10 Hz, 2-pole, low-pass filters for measuring the voltage across the resistor. The engineering conversion to ohms or temperature is done automatically at the full scanning rate in the base VXI module.