niDAQmx analog voltage output and impedance

[go9kata]

Hi guys,

I am using 

Chassis:
NI PXIe-1073
Cards Component:
NI PXIe-6361 & BNC-2111 connector

I try to output an analog voltage square wave pulse in the range of [0,1] V that regulates a laser Cobalt Mambo. The amplitude of the analog signal should modulate the laser strength, where its maximum should be around 1V. The problem is that at 1V I manage to get roughly 40% of the total laser strength. I tested the laser with Axoclamp instrument generating again 1V and I reached the 100% of the total laser strength. I checked that the laser expect impedance of 50ohms. I measured the impedance on the Axonclamp and I got 45 ohm but the one from the NI instrument was ~32ohms. That was my only rationality behind why 1V in two different instruments does not generate the same laser strength. 

My question is during the analog voltage pulse generation is there a way to set the output impdance too?

Here is how I generate the voltage pulse:

TaskHandle  taskAnalogOut = 0;

DAQmxErrChk (DAQmxCreateTask("Analog",&taskAnalogOut));
DAQmxErrChk (DAQmxCreateAOVoltageChan(taskAnalogOut,"PXI1Slot2/ao0","",0.0,1.0,DAQmx_Val_Volts,NULL));
DAQmxErrChk (DAQmxCfgSampClkTiming(taskAnalogOut,"",1000,DAQmx_Val_Rising,DAQmx_Val_FiniteSamps,analog_samples));
DAQmxErrChk (DAQmxWriteAnalogF64(taskAnalogOut,analog_samples,0,10.0,DAQmx_Val_GroupByChannel,analog_data,NULL,NULL));

if(taskAnalogOut != 0)
        DAQmxErrChk (DAQmxStartTask(taskAnalogOut));

 Thank you in advance for any help, suggestions or remarks! 

[Christoph_D]

Hi!

Generally there is a function to set the output impedance of a analog output:

int32 __CFUNC DAQmxSetAOOutputImpedance(TaskHandle taskHandle, const char channel[], float64 data);

But in your case your card has no adjustable impedance.

By the way the specified impedance of the NI PXIe-6361 is 0.2 Ω with a output current drive of ±5 mA:

NI X Series Multifunction Data Acquisition - Data Sheet - National Instruments
http://sine.ni.com/ds/app/doc/p/id/ds-151/lang/en

Perhaps have a look at your specs if the output drive of the ni PXIe-6361 is sufficient for your laser modulation.

Kind regards

Chris