Stream at higher sample rates using different gains.

3 posts / 0 new

Fri, 10/23/2015 - 00:59

erikhaverkamp

Hi,

I would like to stream 2 differential channels at 10kHz with my U6. When I set the input to LJ_rgBIP10V for both channels it works fine. If I set one of the channels (or both) to LJ_rgBIP1V, I get an error.

LabJack Error #60: Stream scans overlapped occured at LJUD_eGetS (DBL Array).vi

So somehow I guess the lower range has an influence on the speed. Does this mean I cannot stream 2 different input ranges at 10kHz? I am unable to find it in the documentation, but I am sure that is my own fault....

Thanks,

Erik

Fri, 10/23/2015 - 09:16

LabJack Support

The information is here:

https://labjack.com/support/datasheets/u6/operation/stream-mode

When doing a multi-channel stream where any channel has a gain > 1, the max sample rate is decreased dramatically. The reason is that auto-settling adds a lot more settling time. There are a couple approaches to go faster:

1. External per-channel amps. If you pre-amplify any signals that need amplification, then all channels can be streamed at Gain = 1. The LJTick-InAmp is a possibility, but it generally is not as good an amp as the U6's internal amp.

2. Manually control settling time. Auto settling chooses a settling time such that a signal with 1000 ohms of source impedance will settle to within the noise band in the time allotted where the previously sampled channel was at an extreme value of +10 or -10 volts. This is quite stringent, so you might be able to use substantially less settling time.

Fri, 10/23/2015 - 11:56

erikhaverkamp

Dear Support,

Thank you for the fast reply. I will try the second approach first!