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DASYLab display lag - live display falls progressively more behind real time


Lsackett
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TLDR: I'm getting lag/delay between the measurement and the live display.

Equipment and worksheet:

- Cheap/new laptop with Ryzen 7 3700U processor and 8GB ram

- Windows 7 Home

- DASYLab 2016 Basic (Release 14.0.0, Build 477)

- MCC DAQ board (USB-1408FS) monitoring 2 draw wire sensors. Connected to the laptop by USB. 1408 is "connected" to DASYLab using InstaCal software.

- SSI meter (Transducer Techniques SSI) monitoring 1 load cell. Connected to the laptop by USB. FTDI driver takes the USB data and simulates a COM port. DASYLab reads the simulated COM port.

- The worksheet does some calculations and writes to a data file.

- Time base in DASYLab is set to 60Hz

- DAQ board set to use DASYLab timebase

- SSI meter set internally to 60Hz

- DASYLab shows a few digital meters and one chart

Everything seems to work fine except for occasional lag. Sometimes the live display keeps up, but sometimes it lags behind real time. When it does lag it seems to get more and more behind. Once, after running for 15 minutes, the display was 2 minutes behind real time. I've tried simplifying the amount of calculations and reducing the amount of data written, but the problem still comes and goes making it hard to troubleshoot.

I have attached the DSB file.

Any suggestions?

Thanks!

RIG Test 1LC ver1.DSB

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Jeffrey, thank you for he help. I downloaded the your file, but it didn't solve the problem.

I did find out that the problem was related to the digital meter module using "automatic" sized fonts - when I changed the font size to "fixed" the lag problem went away. I only figured this out because I looked in the task manager when the lag was happening and found a process called "Usermode Font Driver Host" (fontdrvhost.exe) was using 6-10% of the cpu (which seemed like a lot). I'm running Windows 11 and I'm guessing that the new version of this driver host is glitchy when working with the digital meter module from DASYLab 2016. In case it helps: my laptop is using version 10.22000.832 of fontdrvhost.exe. Perhaps this can be fixed in newer versions of DASYLab (if it isn't already).

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This is a known phenomenon of DASYLab when used with software paced acquisitions as you are using in your worksheet.

This occurs because the timing values used in some of the drivers does not pass the same number of significant digits of a floating point number to the calling software, so after a while there is a time lag.

"How to fix this?"

Change the timebase of the USB-1408FS from DASYLab to USB-1408FS -Input HW, and modify the scan rate to 60 Hz.  This will set the block size to 6.  You can either decimate the data using the separate module:

image.png

or, average the data in the bock using the Average module:

image.png

Keep in mind that DASYLab abhors when data from more than one source,  does not arrive at the inputs of module at the same time.  The fix for this is to write these individual values to Global Variables, and read them into the receiving module such as the Write Data module.  I cannot test your worksheet as I do not have your serial port device, but I have edited your worksheet to include these changes.

457527162_RIGTest1LCver1_rev1.DSB

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