Configuration Setup: AC Calibration

This refers to the AC Response calibration method, and its variants AC Sweep and AC spot. These options may be selected as calibration method in the main tab of the channel configuration screen, as shown below. Notice that “AC RESP” and “SWEEP” are available as calibration method 1, but that “AC SPOT” is only available as method 2 or later.

Setting up a Calibration

To perform the AC calibration on the channels of choice, click in the “AC cal” tab of the channel configuration screen:

  1. AC Response Cal Item Column: calibration item is used to group channels together for calibration, e.g. for channels that will all have the same calibration tone applied simultaneously. For example, all AC Response channels with the same Cal Item can be calibrated simultaneously on the calibration screen. In our example, “ACCEL 1” and “ACCEL 4” may be calibrated together. “ACCEL 3” is on a different calibration item so will be calibrated separately. “ACCEL 2” is on a different calibration method (Sweep), so will also be calibrated separately.
  2. The EU value to be used for calibration. In our example, the calibration signal measured will be worth 10 m/s2 RMS for “ACCEL 1”, and 10 m/s2 PEAK for the 3 other channels.
  3. Calibration item for AC spot calibration.
  4. To launch AC response calibration
  5. To launch AC Sweep calibration
  6. To launch AC Sport calibration

The AC calibration is based on the FFT computed by the calibration service. The size of the FFT is configurable in the Hawk GUI preferences:

Calibration Screen

Upon launching the calibration of choice, the user gets to choose the channels to calibrate. In example below, we have clicked on “AC Resp” button:

  1. Select the calibration item of choice
  2. Displays all the channels within the calibration item selected. Select one or more channels. Multi-select channels by using Ctrl + Click.
  3. Click on “Calibrate” button to launch the calibration, and get to the calibration screen (see below).

  1. For each channel, the thick green bar shows the current amplitude of the highest peak with the FFT computed by the calibration service. The thin bar above shows the amplitude of the last point which was captured at the same frequency. The amplitude measured is shown in the same power factor as the EU power factor selected in the AC cal tab. In our example, RMS for “ACCEL 1” and PEAK for “ACCEL 4”.

    The amplitude bar graph will turn red if the signal is “bad” (unstable). If the user clicks the red bar graph, a popup hint will appear listing the reason why the channel is bad.
  2. For each channel, this shows the current frequency of the highest peak in the FFT. In our example, 1 kHz for both channels.
  3. To show the amplitude in ADC counts or millivolts. Note that during calibration, the user may also look at the raw signals (in millivolts) on the HawkEye real-time screens.
  4. Capture a calibration point (a snap shot of the signals on the calibration channels at this time). Note that for AC sweep, points are automatically captured as the signals change; the capture point button is therefore used once to start the process.
  5. Accept the point just captured. The user may move on to the next frequency and capture the next point. Not available during AC sweep.
  6. Reject the point captured. Not available during AC sweep.
  7. Once all the points have been captured, click on the Finish button to stop the calibration. The next step and final step is to authorise the calibration.
  8. The side panel gives access to the live signal conditioning control panel, allowing the user to change conditioning settings during calibration.

Authorise the Calibration

After finishing a calibration, user may calibrate another set of channels, or authorise the calibrations.

A click in the “Authorise calibration” button brings the user to the authorisation screen:

  1. List of all the channels where there is some pending calibration data to review. Calibration data will be shown for the channel selected in the grid.
  2. Click on the “Auth” cell to change a red cross into a green tick, and vice versa.  
  3. Click on the “Authorise” button to authorise the calibration of every channel flagged with a green tick. As for the channels with red crosses, calibration data will be kept and may be authorised at a later time.
  4. Clicking on the “Cancel” button will discard calibration data for all the channels listed.
  5. For the channel currently selected in the channel list, display the calibration points. The first point (at 0 Hz) is automatically added and has the same amplitude as the captured point with lowest frequency. So is the last point (at acquisition bandwidth), which has the same amplitude as the captured point with highest frequency.
  6. Displays the captured point on a graph amplitude vs frequency. The green line shows the current calibration for the channel (if channel is already calibrated), and the red line is the new calibration, which is being reviewed.
  7. Tick this option to show the captured points on the graph.
  8. To show the amplitude in millivolts or ADC counts.
  9. If calibrations of various types have been performed on a channel, select a calibration type to review the corresponding data.
  10. To delete a captured point.

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