How to stabilize analog input current signal?

[fonder]

Hi,

I am new at NI Labview and I need help. I am trying to measure pressure via 4-20mA Pressure Transmitter. I use NI cDAQ-9138 compact Daq and DAQ 9203 Analog Input(-20/+20mA) module. When I try to reed the signal from the 9203 module, I receive the unstabilized signal as seen as in the image below.

How can I stabilize the signal? What should I do?

[johnsold]

You have 20 uA peak to peak noise on a 4 mA signal. That is about 0.12 % of the full scale span for a 4-20 mA signal. This is probably close to the limit of accuracy of your transducer.  It does not appear to be periodic so it is most likely not due to pickup from power line interference.

One thing which can be done to improve the appearance of the data is to average multiple samples. For example suppose that your system requires one measurement each second. You are sampling at 1000 samples per second. Average 1000 samples and use the average for the once per second values.  Change the numbers to meet your particular needs.

Lynn

[Dennis_Knutson]

I'm just going to add that the signal appears noisy because you are auto scaling the chart. The amount of noise is actually pretty small as Lynn has noted. With averaging and the chart set to a reasonable min and max, everything will look just fine.

[fonder]

Actually our sensor's accuracy is %0,04FS, and noise is not 20uA but 200uA, so noise is %1,2FS, thanks for your advice about power line interference, I will use another power source for transducer.

By the way how can I take avarge of 1000 sample, I tried to take avarage with shift-register and mean.vi but taking so much data with shift regidter is too hard. Is there a vi or any other way for this purpose?

[Dennis_Knutson]

You have not shown any code so it's impossible to say but if you are doing on-demand sampling like the test panel, simply change to continous or finite samples. You get an array. The size is based on the number of samples requested.