DAS Output Configuration

DAS Output is a real time streaming service that computes results from acquired data and streams them to a target device using standard ethernet protocols in an HGL-specified message format. 

DAS Output processes data two ways: Using FFT computations (for order tracking, band pass results, and phase (requires a 1/rev tachometer channel) or using time domain computations (Full Band RMS, Max, Min, Average, etc). Up to 16 different calculations can be performed on any channel. This will be saved to the procsettings.ini on the host Hawk and is usually sent as a setup-message from the target computer.

Time to calculate a frequency domain result is based on sample rate and FFT size. The service update rate will determine when each calculation is performed. For large FFTs and fast service update rates, the FFTs will overlap. The service update rate defines the base processing block duration, in ms it is 1000 / update rate (processing block duration D). 

For example, 20 Hz update rate gives D= 50 ms and a 1k (1024) FFT.

FFT Calculation: 

  • Every 50 ms, the service will compute an FFT over the last 1024 samples (FFT size is specified in INI file). Order track results and band pass calculates are calculated from that FFT. The overlap between FFTs will depend on update rate, sample rate and FFT size.
  • If the channel's sample rate is 25,000 Hz, it takes 40 ms to calculate the 1k FFT. 
  • It is not necessary for the processing to be gap-less. Decide on the FFT size based on the requirements for processing. Fast moving results require small FFTs.

Phase and Order Tracking Calculation:

  • Phase is calculated in frequency domain. A complex FFT is calculated for both the target channel and the tachometer channel.
  • At the identified EO bin, the resultant phase [expressed as arctan(imaginary/real)]. The target channel phase value LEADS the tachometer value. e.g. Phase > 0 means the target is leading the reference tachometer.
  • For pseudo phase calculation, a temporary OPR is generated from the multi-tooth channel and the offset will vary between runs.
  • Order Tracking will identify the bin based on the frequency of the desired EO and determine the amplitude of the signal at that peak.

Time Domain Results:

  • Every 50 ms (D ms), the time domain result is computed over the processing block. Processing blocks are contiguous.
  • When computing the time domain average or RMS, the published results can be smoothed by specifying an average time period in the INI file (AvgAveragePeriodMs for the average result, and RMSAveragePeriodMs for the RMS result). For example, if AvgAveragePeriodMs is set to 500 ms and the update rate is 20 Hz, then the average result of the last 10 "block average" values computed ("block average" being the average of the samples contained in a processing block, in our example 50 ms processing block) is published. If RMSAveragePeriodMs is set to 500 ms, then the RMS value published will will be the average of the last 10 RMS values computed.
  • There are 2 ways of performing the smoothing average: either just a standard mean or a rolling average. To use a rolling average, set the RollingAverage value in the INI file to 1. The rolling average is computed using a smoothing average of N values. Call Ri the result published at update i (and Ri-1 the result published at update i-1), and v the value computed at update i (and RMS or average value), then Ri = (((N-1) * Ri-1) + v) / N

Note: In the [General] Section, to support custom EO tracking widths, add the following:

Version=2

Defining a Target for DASOutputService

The DASOutputService.ini is what tells the software where to send the data.

Newer versions of DASOutputService Allow for 2 Targets to send data too, Edit the Target Address and Target Port to point to the machine receiving data. Any networked target system can receive data from DAS Output Service including Windows, Linux, Labview, etc.

Proc Settings.ini Configuration

DAS Output will process data based on the setup file which will be saved to disk as "ProcSettings.ini". If a setup file is not sent, then the ProcSettings.ini can be created by hand. An example channel is shown on the right. 

  1. The first line defines which channel will be displayed. [Chan1 Mag1]. Up to 16 outputs are allowed on each channel.
  2. "Type= " is an integer value for the type of processing to be performed.
    • Type 0 is None.
    • Types 1-3 are frequency-based calculations and allow for integration via unit conversion.
    • Types 4-9 are time-based calculations and do not allow for integration.
    • The processing types are:
        1. Band Pass
        2. Tracked Order
        3. Phase
        4. Max
        5. Min
        6. Average
        7. Peak
        8. RMS
        9. Instantaneous
  3. Settings available for each type:
    • For Type=1 (Band Pass)
      • Start Frequency=
      • End Frequency=
      • Data Type= (1...4)
        • see Description Below
      • Unit= 
    • For Type=2 (order tracking)
      • Engine Order=
      • Tacho Number= (1...10) - not the tacho number but the tacho index
      • Data Type= (1...3) 
      • Unit=
      • Start Frequency=
      • End Frequency=
      • TrackWidthType= (0-2, Description below)
      • TrackWidthValue= (Description below)
    • For Type=3 (phase)
      • Engine Order=
      • Tacho Number= (1...10)
        • Note: This requires the tacho index value not the tacho number
    • For Type=4 to 9
      • This is full band, time-domain processing.
      • There are no additional settings.
  4. Data Type
    • Type 1: RMS
    • Type 2: Peak
    • Type 3: Peak to Peak
    • Type 4: Max
      • Only available for data type=1
      • This will look for the max amplitude in the frequency band.
  5. EO Track Width: For TYPE_TO or TYPE_PH
    • Track Width Type (0, 1, 2)
      1. Constant Track Width
      2. Q Factor
      3. Percent EO
    • Track Width Value
      • For Type 0: Width is [W Value] in Hz
      • For Type 1: Width is EO Center Frequency / [W Value]
      • For Type 2: Width is EO Center Frequency * [W Value] /100