Montoring a 5 V signal on a digital line and also an analog channel which is more accurate?

[caunchman]

  I have a quesiotn here.  I am using a DAQ 6015 and I set up a quick while loop in LabView in the while loop I used DAQ assistant to monitor a 5 volt signal that is coming off an optical isolator.  At the same time I am monitoring that 5V line on a digital line.  I write both of these values to a measurement file.  It seems as though the digital line is capturing the event much quicker? I don't see the drop on the analog channel for at least 50-75 ms.  The analog channel is set to record at 6000 Hz.  Is the digital IO a more accurate way to capture this event?  How fast does the DAQ perform its A/D conversion? How is the senescence of the data handle?

Chris

[J_Thomas]

Hi caunchman

Thanks for posting your questions. The sequence of the data being handled will depend somewhat on how you have programmed your application.  For example, if you are doing software time digital I/O and an analog input in the same while, the while loop will run as slow as the slowest independent sequence of events in the loop. 

• Are the digital input and analog input task in the same while loop?
• How many samples you are reading in your analog input task at a time?
• What kind of digital read are you doing?
• Can you post your VI or a screenshot of the VI?
• Can you post more about the 5V signal that you are trying to measure? Is it analog (sine wave, etc..)? Is it digital? How fast does the signal change value?

To answer one of your questions: the speed of the A/D is defined by the sampling rate. At 6000 Hz it will take .16 ms to collect a single sample.