Showing results for 
Search instead for 
Did you mean: 

niDAQmx analog voltage output and impedance

Hi guys,


I am using 

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! 

0 Kudos
Message 1 of 2



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


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


Kind regards


Staff Applications Engineer
National Instruments
Certified LabVIEW Developer (CLD), Certified LabVIEW Embedded Systems Developer (CLED)

Don't forget Kudos for Good Answers, and Mark a solution if your problem is solved
0 Kudos
Message 2 of 2