:MEASure Subsystem
Use the Measure (:MEASure) subsystem to make parametric measurements on displayed waveforms. Once a valid waveform is displayed, select the command in this subsystem that corresponds to the measurement that you wish to make including results for histograms, marker, eye masks, and limit lines.
In Eye and Jitter modes, measurements are made using statistics on a waveform database. In Eye mode, you can change the peak number-of-hits required in the color grade database before a measurement is made using the :MEASure:EYE:COMPlete command.
- To return reliable scalar measurements.
- To return measurement results shown in the tables.
- If a measurement cannot be made.
Displaying a Valid Waveform
To make a measurement, the portion of the waveform required for that measurement must be displayed on FlexDCA. For example,
- For a period or frequency measurement, at least 1.5 complete cycles must be displayed.
- For a pulse width measurement, the entire pulse must be displayed.
- For a rise time measurement, the leading (positive-going) edge of the waveform must be displayed.
- For a fall time measurement, the trailing (negative-going) edge of the waveform must be displayed.
Making Measurements
If more than one period, edge, or pulse is displayed, time measurements are made on the first, left-most portion of the displayed waveform. When any of the defined measurements are requested, FlexDCA first determines the top (100%) and base (0%) voltages of the waveform. From this information, FlexDCA determines the other important voltage values (10%, 90%, and 50% voltage values) for making measurements. The 10% and 90% voltage values are used in the rise-time and fall-time measurements when standard measurements are selected. The 50% voltage value is used for measuring frequency, period, pulse width, and duty cycle with standard measurements selected. You can also make measurements using user-defined parameters, instead of the standard measurement values as explained later in this topic.
When the command form of a measurement is used, the measurement result is displayed in the results panel:
:MEASure:EYE:EWIDth
When the query form of the measurement is used, the measurement is made one time and the measurement result is returned.
:MEASure:EYE:EWIDth?
Also,
- If the current acquisition is complete, the current acquisition is measured and the result is returned.
- If the current acquisition is incomplete and FlexDCA is running, acquisitions will continue to occur until the acquisition is complete. The acquisition will then be measured and the result returned.
- If the current acquisition is incomplete and FlexDCA is stopped, the measurement result will be "9.91E+37 which represents Not a Number (NaN)".
You can also return the measurement results of every measurement that is listed in all displayed measurement results panes that are displayed below the graticule. Use the :MEASure:RESults? query. The following is an example of three measurements returned in Eye mode. Line breaks have been added to make the string easier to read:
Name=Eye Width[Time],Source=1A,Current=9.458E-11,Min=9.436E-11,Max=9.458E-11,Count=1.9E+1, Name=Fall Time,Source=1A,Current=2.366E-11,Min=2.366E-11,Max=2.366E-11,Count=3.9E+1, Name=Rise Time,Source=1A,Current=2.366E-11,Min=2.366E-11,Max=2.366E-11,Count=4.4E+1
All measurements are made using the entire display, except for vRMS which allows measurements on a single cycle, and eye measurements in the defined eye window. Therefore, if you want to make measurements on a particular cycle, display only that cycle on the screen.
Measurements are made on the displayed waveform specified by the measurement's child :SOURce command. For example, to make a risetime measurement on channel 1B use the following commands:
:MEASure:OSCilloscope:RISetime:SOURce CHAN1B :MEASure:OSCilloscope:RISetime?
Most measurements are only made on a single source. Some measurements are more complicated, such as the delta time, and can be made on one or two sources with additional waveform parameters specified.
:CHAN1A:DISPlay ON :MEASure:OSCilloscope:DELTatime:ENUMber1 1 :MEASure:OSCilloscope:DELTatime:ENUMber2 2 :MEASure:OSCilloscope:DELTatime:EDIRection1 RISing :MEASure:OSCilloscope:DELTatime:ETHReshold1 MIDDle :MEASure:OSCilloscope:DELTatime:EDIRection2 RISing :MEASure:OSCilloscope:DELTatime:ETHReshold2 MIDDle :MEASure:OSCilloscope:DELTatime