Simultaneous sampling of analog and digital channels of a PCI-6255 using an analog trigger

[JoHo]

Hello,

I am struggling some time with one problem. A have a PCI-6255 80 channel AD card. I want to sample simultaneously 64 analog input channels and one digital input channel. The readings should be triggered with an analog trigger (1kHz). Therefore I am using attached Labview VI. For convenience the VI is just for a single analog input channel.

I have put the analog trigger on the PFI8 event channel. For the digital channel I am using the port0/line1. The analog channel is AI44. The VI seems to read correct. However, the digital and the analog channels seem to be not synchronized. For instance, if I trigger PFI with 1 kHz and I put twice a 500Hz signal TTL square signal on port0/line1 and AI44, the signals of the digital and analog channels are shifted every now and then. I have excluded any problems with the signals themselves and they are stable on the scope.

Is there a solution for this problem?

Thanks you very much in advance!

[Alex_Pi]

Hi,

Before I start explaining how to correlate AI and DIO, I want to point out that the M-series is NOT capable of simultanous AI, because it is multiplexed.

how ever, when using only one Channel this works because the ADC has ot to be shared between channels.

It then is called Correlated DIO. Here are some examples:

Correlated Digital Input Using Analog Input Task in DAQmx

https://decibel.ni.com/content/docs/DOC-5264

Correlated Analog Input, Analog Output, Digital Input, and Digital Output

https://decibel.ni.com/content/docs/DOC-10595

Performing Correlated Digital IO with an M Series Device in LabVIEW

http://zone.ni.com/devzone/cda/epd/p/id/1566

Simultanous Sampling is only possible, when having one ADC per Channel that can share the same sample clock, which is the case for 61xx S-Series ("S" for simultanous)