I was connecting a loop powered pressure transmitter to one channel of SCXI 1102 through SCXI 1308 current input connector block. The scxi is connected using PXI 6229 and its running Windows XP. when the transmitter is at 0 reading 4mA out is converted to 1 volt and being shown in MAX test panel. but its fluctuating between 0V and 1V, and but when I pull the negative signal lead to chassis ground, then the fluctuations are absent and signal is steady at 1 V, why is this happening as for current signals negative lead ground referencing is not required. what could be problem. (also this problem occurs only when I use cable length of more than 15 meters). how to solve this problem.