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LJfg: Delay until end value (square wave output)

function generator ljfg exponential delay square wave

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#1 Lab_Jack

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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!

 

Lab_Jack



#2 LabJack Support

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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:

 

/support/u12/users-guide/2.2

 

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.




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