Need advice on which DAQ module to choose

[mpaurisse]

Hello there!

I am looking for a DAQ device for different applications.
I identified 2 main applications :

1. the acquisition of 2 signals coming from to different sensors (photodiodes -> voltages ranging from 0 to 5V) at relatively high speed : 1 ms between each sample is desired. As a result, the needed temporal resolution of the device would be 1kS/s. An amplitude resolution at 1 mV would be nice.
2. the acquisition of 9 signals from 9 different sensors (photodiodes, and temperature sensors), for a long time, at a relatively low repetition rate (2 S/s max). Amplitude resolution at 1 mV is desired too

For these applications, the data will be acquired via homemade Python software, on a Windows platform.

Before looking at the various models of DAQ, I would like to clarify some points :

- do these DAQs device have internal memory? My understanding is that they don't. So basically every data collected is passed on to the computer directly, am I right?

- if there is no internal memory, is the maximum desired sample rate of 1kS/s simple to maintain on a USB link? Or do I need special additionnal equipment for that?

- do these DAQs have an internal clock? I suppose they do, in order to guarantee a given sampling rate. If so, what is the precision of this clock? In the first use case, I would like to have a rather precise timestamp for each measurement, say 500 µs jitter maximum for a 1 ms resolution. Is that possible directly with the DAQ, or do I need an external trigger for such an application?

Looking at the Digilent website, I identified these DAQs, which seem to suit my needs:

- MCC USB-1608G : high sample rate, sufficient number of inputs. Question : the sample rate given is per channel, or in total?

- MCC USB-1608FS-Plus : sufficient sample rate, simultaneous acquisition (not sure what this means). Number of inputs : 8, so I would need one more, but this can mitigated.

Anyway, I hope I made myself clear about my needs and the questions I have, and I would gladly appreciate any help on that subject.

Thanks!

 

[Fausto]

Hello @mpaurisse.

If you are using thermocouples for your temperature measurements, then neither the MCC USB-1608G nor the MCC USB-1608FS-Plus will suffice for your 2nd application.  Consider the MCC USB-2416-4AO, which supports voltage and thermocouple measurements. 

Neither of these devices have significant amount of storage memory, just what is needed to pass the data up the USB pipeline.  Data storage is maintained on the host system.  Additionally, there is no issue maintaining a capture rate of 1 kS/s.  

These devices have internal clocks, but timestamping is not supported and an external trigger is not required for each sample.  Internal clock specifications are not available in the user's guides, but the jitter is well less than 500 µs jitter.

43 minutes ago, mpaurisse said:

- MCC USB-1608G : high sample rate, sufficient number of inputs. Question : the sample rate given is per channel, or in total?

The sample rate is aggregate, since the analog input channels are multiplexed.

45 minutes ago, mpaurisse said:

- MCC USB-1608FS-Plus : sufficient sample rate, simultaneous acquisition (not sure what this means).

All selected analog input channels are sampled at the same time.

Hope this helps with your decision.

Regards,

Fausto

[mpaurisse]

Thank you for your answer.

From what you said, I think the biggest problem will be the absence of timestamping. If the data is directly passed on to the computer, then I would have to let the computer (my acquisition program more precisely) do the timestamping each time a sample is received.

Doing so, I am afraid that the timestamping may vary according to the load on the host. Do you have any experience on that?

And just to be sure, do you offer some DAQ device that include a timestamping option?

Regards,

[Fausto]

Your code should determine the start time of the acquisition and knowing the sampling frequency, a user can add a timestamp to each data point after the acquisition.

Sorry, no daq hardware offerings with built-in timestamping.

[mpaurisse]

Ok thanks for your help