The Challenge:

Building a simple yet effective PC based data acquisition system for the calculation of burn rate parameters of the rocket propellant (solid or liquid) by acquiring data from a single channel, providing a digital trigger to ignite the propellant.

Solution:

Using National Instruments Lab VIEW software (7 Express) and high speed DAQ (PCI-6036E) hardware to develop an accurate and reliable data acquisition unit.

Introduction:

The performance of the propellant, which forms the fuel of any launch vehicle, has to be evaluated by many means like the calculation of the burn rate, which is one of the most important parameter. Acoustic Emission method for calculating the time taken to burn a known length of the propellant sample at a known pressure will give the burn time based on which the burn rate is calculated.

The Burn Rate Evaluator software successfully meets this requirement by acquiring data from a selected channel of the DAQ card, which in turn connected to the Acoustic Emission strand, hence calculating the burn rate and associated parameters. The software allows the user to set a digital line high for a fixed duration through which the propellant sample is burnt. The acquired data is then continuously logged with the corresponding time stamp every second without any data loss which helps in the offline analysis.

System Configuration:

The data acquisition system uses the DAQ card (PCI-6036E), which in turn is connected to the Acoustic Emission strand through an interface unit. The control room setup consisted of a host PC where the entire channel related configuration is performed; the data from the Acoustic Emission strand is acquired and logged.

System Implementation:

The entire software is divided in to three parts, namely configuration, acquisition and processing.

1 shows the screen for setting the configuration parameters and selecting any one among the available 16 channels on which the data has to be acquired. Here the rate at which the data has to be acquired, the pressure at which the propellant has to be burnt and the sample length of the propellant, run number and the threshold value that is used to calculate the burn rate parameters (Standard deviation, Co variance and Average) are entered.

During acquisition the data from the selected channel will get displayed on the graph as shown in fig 2. The software allows set a digital line high, which in turn provides trigger pulse to actuate the burn of the propellant fuel. When the acquired signal value falls below the threshold continuously for a duration of 3 seconds the acquisition stops automatically and the burn rate with respect to threshold and with respect to lowest peak (which the software calculates) will be get displayed on the table for similar pressure data’s. Option is provided to change the burn rate by selecting the appropriate cursors. The burn rate parameters (Standard deviation, Co variance and Average) can also be viewed for the similar pressure data displayed on the table. These data’s saved on to a file, which helps in offline analysis.

In offline analysis the pressure exponent (Intercept and Slope) of burn rate with respect to threshold and burn rate with respect lowest peak for the already conducted test is viewed. Fig 3 shows the screen for the calculation of the pressure exponents. Options for printing of the waveforms that are acquired during test is provided which helps in documentation.

Conclusion:

The PC based data acquisition system for calculating the burn rate is found to be very accurate reliable and versatile allowing it to be implemented anywhere for similar applications. The flexibility in using the software is an advantage allowing anyone to work on it.