Hawk GUI: Acquiring Data

In order to acquire data, it is necessary load a complete and valid channel configuration.

Record Data

From the general configuration page, click on the “Acquire Data" button:

If the “Acquire Data” button is disabled, that means the channel configuration is not fully setup; most likely one or more channels are not yet calibrated.

The Hawk controller will then configure each element of the system, in particular the Hawk acquisition engines and their attached real-time services. A progress bar indicates how far we are in the process:

A secondary progress dialog may appear while the signal conditioning hardware (internal and external) is configured. If there is no conditioning or the channel count is low, the dialog might appear only very briefly.

We are now in the data acquisition screen. The system shows that it is configured (1), the overall system state is Ok (2).

Double clicking on the system state (2) will take the user to the system status screen. The system status screen is similar to the system setup screen, but in read-only mode.

The user is now able

  • To go to scanning (3),
  • To release the system and come back to the general configuration screen (4).

IMPORTANT: in configured state, the signal conditioning is fully set up. For strain gauges, that means the required voltage is applied to the Wheatstone bridge, allowing the strain gauges to heat up to the optimum temperature.

Scanning

In scanning state:

  • Numeric data values are acquired by the acquisition cards, and streamed to the Hawk acquisition engines,
  • The real-time screens come out of their minimised state.
  • The numeric data values are processed in real time by the Hawk acquisition engine and its real-time services, processed data values are sent out to the real-time screens for display
  • But the data values are not recorded to disk – this is digitisation without capture

The system shows that it is scanning (1). From there, the user may:

  • Stop scanning and come back to configured state (2)
  • Start writing (3)

The speed channels are being processed, the RPM value is displayed in real time for each of those channels (4).

The data time stamp is displayed (5); at this stage it is the machine time of the master Hawk acquisition engine. We are not locked on an external time source (if available).

Writing and Data Time Stamp

If an external time source is available, we can tell if the system has been able to lock on to it (2). The possible external time sources are:

  • IRIG-B through any of the acquisition inputs, as long as the channel has been defined in the configuration as an IRIG channel. There can only be one IRIG channel in a configuration. Once in scanning, the IRIG signal will be decoded in real time, via software, by the IRIG service on the Hawk machine which is the “owner” of the IRIG channel.
  • IRIG-B through a specific IRIG board. In this case, the IRIG signal goes in through a dedicated input, and is decoded as soon as the card is powered. So, the time signal would be available even when the system is IDLE.
  • GPS through GPS receiver board.

At the time of going to writing, if we are locked on the external time source, the system will switch to using that time for marking the captured data. The acquisition data time (5) will become the external time (1), the EXT indicator (4) will be lit up, and PC time (3) will go grey. The external time will be used to time stamp the recorded data.

If at the time of going to writing, we are not locked on an external time source, the master Hawk PC time will be used to time stamp the data. In this case, the PC time indicator (3) will remain lit up, and the EXT indicator (4) will remain greyed out.

During writing, the same time source (master Hawk PC time or external time) is used by every Hawk to time stamp the numeric data files that are recorded.

The “slave” Hawks re-align their time to the master Hawk at time of Start Write. From this point, they count the time based on incoming samples and the expected sample rate. Because the acquisition cards are hardware synchronised (the master acquisition card gives the clock to the slave cards), there will be no drift between any of the acquisition channels.

Now, in the case of an IRIG source acquired via a regular acquisition channel, the acquisition system may slowly drift in relation to the IRIG signal, in other words the time associated to sample X by the system may shift compared to the time computed from the IRIG signal, for the same sample. Any IRIG drift is measured by the Hawk acquisition engine that owns the IRIG channel, and is shown in the top right corner of the acquisition screen:

If the IRIG source is acquired via the IRIG board, the clock signal is generated from the IRIG signal, and therefore there will be no drift. IRIG synchronization is recommended when using the HGL system together with another acquisition system, and both systems use a common IRIG time source to time stamp the data.

Related Articles