How do I get two analog inputs from different devices?

[hurang]

I want to receive analog input from one labview Vi at the same time through two DAQ devices (USB-2020, USB-1808x). However, only USB-1808x works, USB-2020 does not work. I need to receive 2 analog inputs from USB-2020 and 4 analog inputs from USB-1808x.
Each device works fine in each vi, but when combined into one, only one works.
I tried combining each device by creating a sub vi, but it didn't work.
Can you help me with this problem?

[JRys]

There are two Samples per Channel settings, one is on the ULx Timing VI and used to size the buffer. The other one is on the ULx Read VI and is used to request data from the buffer. It also seems to work better when the same amount of data (timing wise) is read from both. Attached is an example that reads 0.1 seconds of data from each device. I have to warn you, it's fragile and if one device holds up the other a buffer error will happen. 

USB2020_USB1808X.vi

[hurang]

Thanks for your reply! Both devices work well at first, but after 1 second, the signal from the USB-2020 device does not appear. I received the same amount of data as you recommended. There is no buffer error. I will attach the VI I created. thank you.

USB2020_USB1808x.vi

[JRys]

Here are a few suggestions:

• Record one file for each device. 
• Change the file type to Binary TDMS.
• Reduce the USB-2020 sample rate
• Increase the USB-2020 buffer size to 8,000,000

Refer to the attached VI as an example of these changes. 

USB2020_USB1808x2.vi

[hurang]

First and foremost, I'd like to express my sincere appreciation for your detailed response to our previous inquiry. Your insights and guidance have been invaluable to us.

1.In your last response, you recommended to "Reduce the USB-2020 sample rate." However, our target sampling rate must be at least 1MHz. When operating simultaneously on USB-2020, the signal abruptly stops working after about 2 seconds, with an error appearing specifically on the 2 channels of the USB-2020, as shown in the attached photo (See Attachment 1).

2. Could the computer specifications possibly influence the reading of the data? I will attach a photo (See Attachment 2) of my laptop's specifications for your reference."

3. In your previous feedback, you mentioned to "Increase the USB-2020 buffer size to 8,000,000." Could you explain the rationale behind setting the buffer size to this specific number? I've included a snapshot for your reference (See Attachment 3).

4. You also advised to "Record one file for each device." We intend to receive data for each channel in separate folders. Could you elaborate on the reason for your recommendation?

5. In a previous response, you explained the importance of timing and buffer management when using multiple DAQ devices simultaneously, highlighting the roles of the ULx Timing VI and ULx Read VI. You stated that the ULx Timing VI is used for buffer size setting, and the ULx Read VI is used to request data from the buffer. How should these ULx be configured when aiming to receive data from 6 channels simultaneously, with the 2 channels corresponding to the USB-2020 requiring a minimum sampling rate of 1MHz?

I look forward to your insights on these matters. Once again, thank you for your unwavering support and guidance. We truly appreciate your assistance in helping us tackle these challenges.

Warm regards,

 

[JRys]

1. Ensure that your USB-2020 has the latest firmware. The firmware should be 0.26 and 0.92 for the FPGA. If need be, you can update the firmware by doing the following. Download the USB-2020.iic file and copy it to C:\Program Files (x86)\DAQ\FirmwareImages\. To update the firmware, run InstaCal and choose the Download Firmware... from the Install menu. 

2. I can run the USB-2020 continuously at 2 MS/s. My computer has an Intel i9-10920X 3.5 GHz, 64 GB RAM, and an M.2 SSD. 

3. Usually, I recommend a one-second buffer, so if the same rate is 1,000,000, the buffer would be 1,000,000. However, you also use a second device, so make it bigger. For 1 MS/s, I suggest 2,000,000. Read half at a time, so Samples to Read would be 1,000,000. Better yet, read 100,000, which is 0.1 seconds.

4. Creating multiple files and writing to each one takes longer than a single file. Text files take more time, too. It's up to you to test multiple files vs sample rate. You may find that with multiple files, 1 MS/s is not possible.

5. We do not test multiple device configurations. I suggested reading 0.1 seconds of data each time to update the displays frequently. You are responsible for trying other configurations to find what works best for you.