DAQ - Common Mode Noise

Common mode noise happen when the ground potential between the measuring instrument and the device being measured are different. The ground potential will result in ground loop and a current flowing through ground and the low lead. Experiment Example 1: Hardware DAQ-2206 x 1, PS-24V, PS-12V, resistor divider. Procedure PS-24V and PS-12V supply voltage to resistor divider, then measure the voltage across the resistor using Differential Mode. First without AIGnd and check the reading Second with AIGnd and check the reading  Result Without AIGnd, reading unstable. With AIGnd, reading stable Experiment Example 2: Hardware HSL-AI16AO2 x 2, PS-24V, PS-12V, resistor divider.   Procedure PS-24V and PS-12V supply voltage to resistor divider, then measure the voltage across the resistor using Differential Mode. First without AIGnd and check the reading Second with AIGnd and check the reading  Result Without AIGnd, reading unstable. With AIGnd, reading stable Summary In differential mode measurement, if AIGnd are not connected to common ground between measurement instrument and devices and common mode noise occur, reading will be unstable. Hence require to connect the AIL to AIGnd to common ground between them. Notes http://www.vtiinstruments.com/SupportBx4Qans.aspx?FaqID=130