I am using
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!
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.