Signal Issue with CDAQ 9185 and NI9201

[rinkumittal]

Hi, 

I am taking data from the accelerometer using CDAQ 9185 and NI920. I am not getting the smooth sinusoidal signal. The signal I am getting is shown in image 1. This kind of signal is coming even when I remove the sensor. I have also changed the sampling frequency and continuous mode. The sensor I am using of PCB make 356A44. I am not sure why the signal is not coming smoother as the sinusoidal curve.

Please help me in this regard.

R K Mittal

[ZYOng]

PCB 356A44 is an ICP accelerometer, which requires excitation. NI-9201 is a general voltage input and cannot provide excitation. You should a module that supports IEPE excitation and measurement like NI-9234.

[rinkumittal]

I am using a signal conditioner which provides current to the accelerometer. We are getting responses in all directions, and It also changes, but we are not getting a smooth signal. We get the response as shown in the image which is not smooth curve. 

If we do not attach any sensor, we get this kind of signal.

we are not sure why we are not getting a sinusoidal curve. We have used other NI Daq previously, but we have a smooth curve.

Regards

RK Mittal

[ZYOng]

I saw that you are using On Demand sampling mode in the Test Panel. On Demand mode is software timed. Try using Finite or Continuous mode instead.

As for the data without any sensors, from Incorrect Readings on Unconnected or Open Channels of DAQ Device

NI does not specify what voltage a device will read when there is no signal connected.

Since an open or unconnected channel is not being actively driven to any specific voltage you cannot expect a specific voltage to appear on the channel. To see zero volts on a given channel, there will need to be a zero voltage signal applied across the + and - terminals of the channel, which is the same as grounding the channel. To pull down the signal to zero, you can use a pull-down resistor.