
Noise when more than 1 signal is connected (Easy stream example)
#1
Posted 16 January 2013 - 09:46 AM
#2
Posted 16 January 2013 - 10:02 AM
#3
Posted 17 January 2013 - 04:40 AM
One test is to see if it is a general problem, or unique to these sensors in your setup. Try some other signals in your stream to see if they are affected:
-Tied to GND.
---------->The problem doesn't occur
-1.5V AA battery or similar.
---------->The problem doesn't occur
-Different temperature sensor such as LM34 (labjack.com/support/app-notes/temperature-sensors).
---------->I have tried with 2 pressure sensors (attached file n°1). The reading is correct (attached file n°2)
Do you see the problem in command/response mode (try LJLogUD), or just in stream mode (can test with LJStreamUD in addition to the VIs)?
---------->When using LJLogUD, I get attached file n°3 : both signals seem correct. When disconecting one of them the other stays the same. From what I understand in the program it only measures one point where as the Easy stream example takes 1000 Samples on each of the lines.
Attached file n°4 shows my problem. As the matter of fact it is not a noise problem but the dropping of the voltage you can see on the graph (mainly on channel 1(red curve)). When I disconnect sensor 1 on channel 0, the red curve gets correct (attached file n°5) and the data changes from 0.97V (sensor1 connected on channel0 and sensor 2 on channel 1) to 0.93V (when only sensor2 is connected)
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Attached Files
#4
Posted 17 January 2013 - 06:48 AM
#5
Posted 17 January 2013 - 02:53 PM
#6
Posted 18 January 2013 - 05:53 AM
#7
Posted 18 January 2013 - 11:55 AM
#8
Posted 28 January 2013 - 01:54 AM
#9
Posted 28 January 2013 - 10:59 AM
http://labjack.com/s...ers-guide/4.3.7
That means the U6 sends out a USB packet every 25 samples. When it sounds out this USB packet there is a spike of extra supply current, and this could cause the VS supply to droop. We know this does not affect measurements in general (per your results in post #3), so not sure why it might affect your particular signals.
#10
Posted 28 January 2013 - 02:48 PM
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