During a recent consultation a customer was preparing to upgrade a pulse monitoring system.  The tool originally used a standalone pulse generator, but that device did not offer enough flexibility of triggering options. The Analog portion was done on an oscilloscope which had 2 channels where 4 was needed, and which was only able to store a single trigger result before the data had to be manually extracted to a floppy diskette.  Doing multiple tests was very time consuming.

The goal of this experimental fixture was to trigger a laser which transmitted an invisible laser beam through organic tissues.  The structure of those tissues would cause a diffraction pattern for certain wavelengths of light, and the intensity of those transmissions could be recorded using a Photo-Diode Array (PDA) to determine the spatial diffraction pattern.  The PDA would be clocked and triggered but must be delayed a few microseconds.  So the desire was to fire two or more lasers simultaneously and multiple PDA's could be read and recorded, properly synchronized for each laser.

The user was convinced about the power of Virtual Instrumentation and National Instrument's Data Acquisition (DAQ) and was prepared to purchase several modular instruments.  One instrument, they thought, would provide the digital trigger signals while another instrument (or two) would be synchronized to record the analog triggers.  Several Digital I/O (DIO) devices could provide the digital pulses and triggers, perhaps even the Multi I/O "E-Series MIO" devices could do the job.  As for the synchronized analog, the S-Series devices would do the job.  The customer had the order nearly ready for processing.

Enter the new M-Series DAQ devices which changed the landscape of doing such projects.  In general, an M-Series device has more channels, higher resolution, and higher sampling rates, and cost less than predecessors with fewer options.  We theorized that we could do the entire job on a single M-Series board for PXI.

Comparing options on the boards revealed that nearly all of the M-Series boards could generate handle the digital clock using the two embedded counters.  Those can be used to clock the PDA, and another set of static DIO lines would trigger the laser to fire.  Relative to that firing pulse, with a precise delay in microseconds, another static DIO line will be used to start the PDA scanning. 

The biggest surprise on the board was the analog inputs.  One board, the PXI-XXXX was capable of 4 simultaneous sampling analog inputs with XX MS/s per channel.  It was important that the signals were synchronous, and that that rating was not going to be divided among the channels resulting in a reduced sampling rate.  A quick call to NI Technical Support confirmed that the board did indeed have four independent Analog-to-Digital converters simultaneously clocked, and the signals would indeed be precisely synchronized. 

Therefore, if desired, four lasers and four PDA signals could all be simultaneously clocked, triggered, and sampled.   

Another very important new feature from NI is the driver infrastructure for these devices, called NI-DAQmx.  NI-DAQmx controls every aspect of your DAQ system from configuration, auto-generated programming in LabVIEW, and even low-level operating system and device control.  Using previous versions, a lot of trial-and-error was required and many features had to be carefully configured.  Now using examples and auto-generated code, the process is significantly simplified and much more error-proof.

Using LabVIEW and NI-DAQmx, a program for triggering the lasers and the PDA was created, and the analog images were acquired and stored to the hard-drive for further processing.  In the end, the system was able to fire, rearm, and repeat the process multiple times per second, about 220 milliseconds per repetition.