AnsweredAssumed Answered

Automatic cycle time calculation

Question asked by afcec on May 7, 2018
Latest reply on Jul 5, 2018 by DavidVW

Hi,

 

I am using an external application to make automatic antenna measurements using SCPI commands. The software controls both, the VNA and a movement controller which manages several different axes (azimuth, roll, polarisation, etc...). The synchronization between the movement controller and the VNA is done with external triggers using the rear input from the analiser. Everything works as expected but now I need to take the system to a higher level in terms of speed. Therefore, during the mesaurement definition I need to calculate the maximum velocity for the axis and that maximum velocity is limited by the cycle time expected with a specific configuration.

 

As a first approach, after the user provides all the required parameters (frequency segments, IF bandwidth, power, etc...) I connect to the VNA to get the sweep time. Taking that sweep time as a reference I thought I could then calculate how fast my triggers could arrive ( I know the sweep time does not take into account important delays like retracing, display update, band crossing, etc...) but unfortunately this was not a good approach as I found great differences during my first experiments.

 

For example, with a specific configuration, the analiser indicates a sweep time of 12.45 ms but my experiments show that I can not send triggers faster than 40 ms, which obviously is a big difference. Therefore, this obtained 'sweep time' as it is is not valid for my calculations.

 

So the question is, given a specific IF bandwidth, frequency sweep configuration (tipically 1 or several segments with N points from A to B), how can I calculate the TOTAL time to complete the sweep and make sure the analiser is ready to receive more triggers? Some comments: I can not use the TRIG READY signal for the synchronization as I need to calculate the axis velocity before starting the measurement. The screen is kept always off to avoid the delay caused by the update.

 

This is a first step and then I need to somehow addapt this method to calculate the same when using Fast-CW mode.

 

Thanks in advance

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