DAQ (LabJack) analog input voltage flickering/noise

[RSC]

Hi guys,

I´m using a LabJack (DAQ-System) to read the voltage of some sensors. LabJack has a tool called LJControlPanel where you can test the data aquisition on your analog inputs. If I use the LJControlPanel to read the output voltage of the sensors everything is fine and i have nearly no flickering/ noise. If i read the output voltage in FlowStone, for some reason i get alot of flickering and noise. What could cause that?
I added two gifs to clarify what im talking about.

For comunicating and reading the Labjack data i use the LabJack Example (http://www.dsprobotics.com/support/viewtopic.php?f=42&t=362).
I think something in the algorithm of FlowStone or the code in the Lab-JackU3-HV module is causing this strong flickering. I cant open the module code so im not able to see what could cause this. Can anybody help me figure this out?

[aronb]

Hi,

I design and build Data Acquisition Systems (since 1980 ), and have used LabJack, and others before, including my own PIC based microcontrollers over USB to FlowStone.

It looks like the LabJack "engine" has some digital filtering, and typically FlowStone runs communications as fast as possible, so it has no filtering - that is left up to the designer / engineer.

NOTE that any filter you make will be a tradeoff between response of the system (lag - it takes time to process out the noise), and how much noise you filter.
I.E. more filtering = larger lag time / slower response, less filtering = smaller lag / faster response.

If you can put in a step response to your input(s), you can test how much filtering is enough, and how much system lag / response is acceptable to you. I typically go with just enough filtering, and try to preserve my system response, since my designs are typically for front panel real time control of lighting, stage, and laser show equipment.

I am at work now, and when I get home I will look through my bag of tricks - maybe there is something that can help

Aron

[RSC]

Hi aronb,

thanks for your advise. Currently im filtering by creating an array for some milli seconds, if it has 10 values stored I calculate the average. Is this a good way to deal with this?

[aronb]

Hi,

The way you are doing you filtering seems fine... For any of my ADC Systems I try and make the signal input / ADC capture as noise free as possible. But sometimes you still need some filtering.

Here are a few things I use (I grabbed them from a few schematics using ADC / Data Acquisition).

Filter_ADC_Stuff.fsm

ADC Filter Stuff

(2.83 KiB) Downloaded 1014 times

There are both Green and Blue connector versions. Typically the ADC comes in over Green Connections, and I need Blue stream data in the end, so often I will do my filtering with slew limiters or some type of circular buffer or capture XX number of samples and average them, and sometimes I do it with just green connections - just like you have shown.

Hope this helps, and good luck,

Aron