The Challenge:

To develop a cost effective and PC based system for performing following functions:

The Solution:

Using the National Instruments PCI based High Speed DIO Card, NI DAQmx and LabVIEW Development environment to create a PC based, cost effective and reliable acquisition system within four weeks.

Introduction:

Our client, a leading R&D organization, specializes in study of chemical reactions. The outputs of one of the chemical reactions is given to a measurement system. The measurement system generates output in the form of digital pulse trains of high frequency. The rate of the digital pulses depends on the chemical reactions. The challenge given to our team was to make a cost effective PC based system capable of accomplishing the following tasks:

• Record incoming pulses of TTL levels from eight channels to the system hard disk
• Analyse logged data files and detect occurrences of pulses (rising edges)
• Display and generate results containing the following:
  

  	1.	Pulses in the order of their occurrence times,
  	2.	Occurrence time of state transitions in the logged data (rising edges) and
  	3.	Time interval between consecutive pulses on the same channel

We selected PCI-NI 6534 for acquiring data from the measurement system. The NI 6534 is a high-speed digital I/O device with two independent timing controllers for high-speed data transfer. It has 32 MB onboard memory. An onboard 20 MHz oscillator generates the timebase on the NI 6534, and data can be transferred at a maximum rate of 20 MS/s, with samples of one, two, or four bytes. Onboard memory of the card and multithreaded DAQmx driver software allowed us to easily achieve a sustained data logging rate of 10 MS/s to the system hard drive.

Our custom data logging algorithms allowed us to overcome the 4 GB file size in LabVIEW and log data till the hard drive gets filled completely.

System Design:

Software Features:

The software developed in LabVIEW provided following features:

• Test Configuration: The software allowed for editing and configuring test parameters like Test Name, clock rate [Sampling rate], and test duration. The user also had options to select the channels to be logged.
• Data Acquisition: The acquisition of data and logging of data were implemented in two independent and parallel loops. This was advantageous as LabVIEW is inherently multithreaded. As LabVIEW has a 4 GB file size limitation, a custom algorithm was developed for logging the acquired data. This algorithm allowed us to create multiple data files each less than 4 GB on the fly without loss of data.
• Analysis: The acquired test data was in the order of tens of gigabytes. The data had to be analysed accurately and results had to be generated as fast as possible. Here again we designed and developed a four stage custom algorithm to effectively scan and analyse the logged data. The four stages are as follows:
  

  	1.	The first stage just read a predefined block of data from the logged data files.
  	2.	To save space eight channel data is encoded and compressed before storing. The second stage takes decodes and decompresses the read data.
  	3.	In the third stage the decompressed channels data is passed through detection algorithms. Multithreading allowed us to analyse multiple channels simultaneously.
  	4.	In the fourth sequence the results are stored in report files

The above mentioned sequence of operations continued till all the data files for the selected test are scanned.

• Result: The user had the option of viewing the analysis results for various time intervals. Results could also be viewed for different values of scaling period, and time resolution. Reports could be easily printed, and custom reports could be stored.

Conclusion:

We were able to design and develop highly accurate and reliable system that enabled our client to efficiently record and detect digital patterns from his test setup. The seamless integration of NI hardware and software ensured quick development. The entire system was developed, tested and delivered in the span of one month. The customer was delighted at the overall performance of the system as it ideally suited his R&D requirements and is now a true believer in the power of virtual instrumentation.