External timebase with bursts of signals with constant period (cycle) time and with delays between the bursts

To use an external timebase with bursts of signals with constant period time and with delays between the bursts follow the steps below:

1. First the possible time periods of the measurement system must be calculated.

   1. Calculate the smallest time interval t1 between two frames that can occur during the measurement (i.e. the smallest time interval between two pulses from the external timebase source that can occur during the measurement).

   2. Calculate the longest interval between two pulses from the external timebase source that can occur during the measurement, multiply it by 1.5 and call it t2.

   3. Calculate the maximum frequency f as 1/ t1.

      The non-periodic sync cannot be faster than 120 Hz due to network delays of the TCP/IP network.

   4. Calculate the number of pulses n that will be generated during the measurement (i.e. the number of frames that will be captured).

2. Set the Marker capture frequency in QTM to f.
   If the Capture rate is set to a value that is lower than f the cameras will flash for a larger part of the time between two pulses, which might lead to overheating of the cameras. It might also result in that the time to calculate marker positions in each frame is too short. Therefore some markers, those vertically lowest, might be lost.

3. Select External timebase (and Non-periodic for Oqus) on the Synchronization page in the Project options dialog.
   External timebase can be used together with an external trigger. If both are used, the first frame will be captured on the first timebase pulse following the trigger event of the external trigger.

4. Set the Max expected time between two frames option to t2 seconds. If no frame has been received by QTM within t2 seconds, QTM assumes that an error has occurred and aborts the measurement.

5. Start a new measurement. The frequency will be reported as EXT in the main status bar, because it is unknown.

6. Enter the number of frames (n) under the Capture period heading in the Start capture dialog.
   It is important to specify the correct number of frames, so that the last part of the measurement is not excluded. However they should not be too many, if the external timebase source stops firing frames after the measurement that would mean that the measurement is never finished. The best way is to specify a few frames extra and then let the external timebase source fire a little longer than necessary, so that all of the required number of frames will definitely receive a pulse from the external timebase source.