Jump to content

As of July 17, 2015, the LabJack forums here at forums.labjack.com are shut down. New registrations, topics, and replies are disabled. All forums are in a read-only state for archive purposes.

Please visit our current forums at labjack.com/forums to view and make new posts. To post on the current forums, use your labjack.com login account. Your old LabJack forums login credentials have been retired. There are no longer separate logins for labjack.com and LabJack forums.


LJfg: Delay until end value (square wave output)

function generator ljfg exponential delay square wave

  • Please log in to reply
1 reply to this topic

#1 Lab_Jack

  • Members
  • 1 posts

Posted 20 October 2014 - 01:46 AM

Hi everyone,


I am trying to use the "Ljfg" application with my U12 to trigger a laser controller. The laser current is directly proportional to the trigger voltage. It is important for my setup to have a very low delay until the maximum laser current is reached. When using "Ljfg", I measure a delay of approx. 20 ms until the maximum voltage is obtained (square wave output). Is there a way to reduce this delay?


Any help is highly appreciated!



#2 LabJack Support

LabJack Support
  • Admin
  • 8677 posts

Posted 20 October 2014 - 09:29 AM

The U12 analog outputs have a filter with a -3dB point around 22 Hz, which would cause slow rise-time:




That equates to a rise-time (Tau) of 45ms.  That is, in response to a step change the outputs should change about 63% of the way to the final value in 45ms.


For a faster 0/5V square wave you could use an IO line, or faster yet a D line.


If you need variable magnitude, I would add some sort of external gate.  You use the AO to provide the input signal to the gate and use a DO to control the gate.


The U6 (Tau=300us) and T7 (Tau=4us) have much faster DAC outputs.

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users