Non-weighed cumulative average in SignalExpress

[Thijs Lanckriet]

I've recently started using Labview SignalExpress 2009 and a USB-6225 to log data from a laser distance meter that provides an analog output 0-10V DC. I'd like to take a 5-second reading of the voltage output (while keeping the measured distance constant) at, say 20 Hz, and calculate the (non-weighed) cumulative mean of the voltage signal to see how much the noise in the output gets damped by the averaging. 

Can SignalExpress create cumulative averages? And should I use the original voltage signal or a scalar variable (such as the DC amplitude of the signal)? Is there a way to turn off the averaging weight functions to get a non-weighed average?

[Aaron_W.]

Thijs,

Thanks for posting on the NI Forums. If you are looking for a way to find a voltage average of your sampling of the signal you could use a Time Averaging function with Signal Express. However, these functions are only installed with the full version of Signal Express and not the LE edition. If you do have the full version you can select Add Step >>  Processing >> Analog Signals >> Time Averaging. This function can be used after you do a DAQmx Acquire step to process the average voltage value of the last signal that was acquired. I don't quite understand what you are meaning by using non-weighted means on the voltage values. Are you looking for the voltage values from the ADC before the driver has scaled the data? 

[Thijs Lanckriet]

Hi,

I do have the full version (not the LE edition) of  SignalExpress, but rather than getting a time-averaged signal, I need an average value of all samples taken up until that point. E.g. when I'm sampling at, say, 20 Hz, and I've sampled for 2 seconds, I've acquired 40 samples: I want the average value of those 40 samples. 1 second later, I have 60 samples, so I want the average of those 60 samples, and so forth, while updating the average value in real-time as more and more values are taken into account. Is this possible in SignalExpress?

[Aaron_W.]

You will just need to set the DAQmx acquisition mode for continuous and then you can set the Time Averaging to "Running Avg." this will provide a continuous running average. I have attached an image.

[Thijs Lanckriet]

Thanks. This is indeed very close to what I'm looking for but in the dialog screen that you show, you can choose between "Exponential" and "Linear" weighing functions, to be used in the averaging. I'd like to have no weighing whatsoever, i.e. that all points in the measurement sequence are equally accounted for.

[Aaron_W.]

Thijs,

I would recommend using Linear averaging, I believe this treats all points as equal when it comes to averaging the signal. Let me know how if that works as you desire.