Smoothness of Analog Outputs


#1

I decided to run a little test today on my test bench in my lab. I was going to test for the delay between inputting a signal and the time gets written out. Instead I found that the output signal was choppy.

My set up is thus:
SNAP PAC R1 (8.4 firmware)
4 Position Rack
Analog Input (AIV-8)
Analog Output (AOV-25)

I ran a signal generator with a sinusoidal Waveform (8V p-p, 4V offset. 0.2 HZ) and an oscilloscope on the signal generator signal and on the AOV.

The program Consisted of two blocks: Move AIV to Variable, move Variable to AOV.

The signal from the AOV module was choppy and had significant steps (about 100 msec) the loop time was around 5msec. I figured as I was in debug mode I would see some slow down but not this significant.

Is there any advice for a higher response?


#2

Interesting test.

The problem is not the output, but the input. The AIV-8 doesn’t meet the specification that is needed for your test. It has a data freshness maximum of 280ms, so you can’t expect it to update its value any faster than that. Your frequency of 0.2Hz is too high for this module to measure.

An AIV 2 channel module is much faster at 11.5ms and would be more suitable for your test. The AOV-25 should be fine as well responding in a few ms.


#3

@philip is correct, the AIV-8 is about the slowest analog input module we have.
It is important for every application that you note the ‘data freshness’ value as Philip points out. This is the speed that the module will provide new data for a change in input.
This applies to both digital and analog modules.


#4

@Beno @philip Thank you for this information. This was the key I was missing. I moved to an AIV-4 (for two channels is as fast as the 2 channel) and found that signal much better.