PXI-4351 reading rate

[ludos]

Hello,

I'm using a 4351 board for RTD and thermocouple measurements. I've got a strange behaviour when activating "auto-zero at start" : the reading rate is higher than with no auto-zero at all. It looks like it was in "Fast" mode, although i leave the reading rate in "Slow" mode.

I'm using a pxi controler with labview RT 8.2.1 and 435x driver 2.5.2.

Any help would be very appreciated

regards

Ludos

[jp_Braud]

Hello Ludos,

Thanks for posting here. I think you should check if by selecting "auto-zero at start" doesn't mean "auto-zero only once". I don't know if it's clear, but I guess depending your acquisition configuration, "auto-zero in each reading" would be the default state. So it will explain why your acquisition is so slow with default configuration.

You can post here your code if you want, so we will have a look into it.

(Please also give us the labVIEW version and the drivers you are using).

Regards,

[ludos]

Hello,

Thank for your answer.
In fact, the acquisition in "Slow" mode is not too slow, it just match the spec (p 2-4 of the NI 435x User Manual), witch is given with no auto-zero : 2.8 readings per second, to be divided by the number of channels.

With 5 chanel (+ 1 for CJC), the acquisition take approximately 2.15s in slow mode, no autozero => 2.8 readings/s
Activating Autozero per scan add 1 channel measurement (around 2.5 s => 2.8 readings/s).
Activating Autozero at start should impact only the first scan... but here, it take 0,7 for the whole scan => 8.6 readings/s. That's near from the Fast mode spec : 8.8 readings/s.

My config is a PXI-8106 RT controler with a PXI-4351. I'm Using Labview 8.2.1 with corresponding RT module. And the driver for the 4351 is ni435x 2.5.2 / traditional DAQ 7.4.4

Regards,

Ludos

[jp_Braud]

Hi Ludos,

It's very interesting... Using the fast mode could make your card acquire 9.1 readings/s (page A-7). But the problem remain the same, you ask for slow mode and you still get an higher frequency wich is the frequency match with 50Hz filter. Could you post here your code (or a small code that reproduce this matter ?

So I will launch it and test it here.

By any chance, could you try in the same time to run an example ?

Regards,

[ludos]

Hi Jean-Philippe,

Here is my sample vi for testing the 4351 board.
While looking at the examples given with the driver, i see that none of them use Autozero "at start". They use Autozero, but in default mode which is "per scan"...

Regards,

Ludos

[jp_Braud]

Hi Ludos,

I tested it here and reproduce exactly the same behaviour.

It's normal to see the "Autozero at start" is faster than "autozero per scan" in both slow and fast modes.

It's strange to see that with "no-autozero", it takes more time... But I don't think it's a problem into your application, isn't it?

I will create an internal action for this. But feel free to call us (or to post here again) if you get troubles with this matter.

Regards,