Noise at analogue input of PCI-7350

[yanxinix]

Hi,

I have a set up as shown below. 

Futek Load Cells >> SCC-SG04>> SC-2345 >>SH68-68EP Cable >> SCB-68 >> Analogue input of PCI 7350 8 axis motion controller.

This set up has resulted in a noisy analogue signal from 7350 with high amplitude spike. 

I had try connecting the signal out of SCB-68 directly to an oscilloscope, and the signal was fairly clean without the spikes. however, when i connect the signal to AI of PCI-7350, both oscilloscope and load ADC.vi readings of the signal became noisy with high frequency noise on oscilloscope. All the AI ports and AIGND ports were probed without other connections showed the same noise problem.

Moreover, after the switching on of 24Vdc power supply for the motors, the amplitude of noise became even higher.

Is there any method to eliminate/minimise the noise pick up at the AI ports?? Any suggestions are welcome.

Thank you.

Yanxinix 

[Buechsenschuetz]

 An essential issue when connecting analogue lines to a system is connecting not only the signals lines properly but also the ground lines. Proper grounding of the signal connections is essential. You should be aware that BOTH lines (signal and GND) carry the signal, and depending on the connection of the GND line excessive current flowing through this line on a section between the system and the sensor may cause excessive noise. Much has been written about proper grounding of analogue signals. The most essential rule is NEVER to let any significant current (besides the current generated by the signal source) flow somewhere between the system and the sensor, i.e. NEVER use the signal GND lines as GND line for the power supply of the sensor. There are tutorials available on this issue on the NI site, try this one: https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...