Cursors are used to measure time, frequency, voltage and level
The screenshot above shows the analog waveform display with all cursors enabled.
Other display formats vary but cursor operation is the same from an operational point of view.
Cursor Types and Movement
For each display there are up to two movable and one fixed cursor per axis:
The origin cursors (ORIGIN) always appear on the display and indicate the ground (zero) reference voltage and trigger point. On spectrum magnitude displays they indicate DC (zero frequency) and nominal (reference) levels. In all cases they effectively mark the axis origin.
The other cursors (POINT and MARK) are displayed only when enabled via their respective tool buttons (X-AXIS and Y-AXIS). These cursors can be located anywhere by clicking and dragging with the mouse. If the cursors are located one on top of the other the POINT cursor is moved first.
Cursor Measurement Values
As the cursors are moved, the measurement variables below the main display update to report their value. In this way any voltage, time, period, frequency or level can be accurately measured.
The reported cursor measurement variables in DSO 2.2 are:
The cursor values are recorded and reported to at least 6 decimal digits resolution.
Off Screen Cursor Location
If a cursor's value is such that it would be positioned "off screen" it will instead be shown "pinned" to the left or right (or top or bottom) of the display.
Consequently it is possible to see which way to adjust the horizontal or vertical offset to locate the cursor onto the display. It also means the cursor is always available to be "picked up" with the mouse (ie, you can't "lose" cursors).
Note "can't lose cursors" does not mean they are not sometimes hard to see.
The display GRID can obscure cursors somewhat (we recommend you turn off the GRID if using cursors) as can the waveform or spectrum itself, or another cursor. In the latter case, a quick drag of the mouse will determine whether one cursor is sitting atop another.
Measurements Shared between Virtual Instruments
While the DSO implements multiple virtual instruments there is only one set of cursors for each type of measurement (ie, time, frequency, voltage and level) regardless of the selected instrument.
This means one can set up cursors and compare values between different virtual instruments.
For example, cursor positions referenced to a logic transition in the LOGIC instrument can be seen on an analog waveform in the SCOPE instrument (assuming one uses the same trigger condition).
Of course MIXED mode provides similar capabilities all on the one display but one may prefer the SCOPE's more powerful waveform analysis tools or to use it to establish a "zoomed in" view.
In all cases the cursor positions are reported the same way making measurements on waveforms captured with in different instruments possible.
Time and Frequency Cursors
The DSO supports TIME and FREQUENCY cursors for precise measurement of time periods, pulse width, delays, frequencies and bandwidths.
These cursors are also useful to indicate fixed time and frequency points when adjusting waveform or frequency offsets, applying a post-trigger delay or adjusting timebases or timescales.
Below is a screenshot showing both cursors on features of the SYDNEY Bitscope waveforms.
In this example, the time cursors are positioned to report the waveform period on channel A (TP=154 uS) and the associated frequency (FP=6.5 kHz).
The frequency cursors are positioned on the first harmonic (fundamental) of the waveform on channel B (FM=13 kHz) and the third harmonic (39 kHz). The frequency difference between the first and third harmonics is 26 kHz (FP=26 kHz).
These measurements in both time and frequency domains are consistent (the waveform on channel B is precisely twice the frequency of that on channel A).
Some other statistics to note are the display sample rate (FS=500 kHz), the total spectrum bandwidth (FN=250 kHz) and the time span of the waveform display (TN=500 uS). Also, the left edge of the time display is TD=178 uS after the trigger point.
In normal usage, to measure a single time or frequency value (referenced to 0 Hz or the trigger point respectively) simply move the Point Cursor (RED) to the position you wish to measure. If you want to measure the difference between two times or frequencies, move the Point Cursor to the right point (first) and the Mark Cursor (WHITE) to the left point (second).
Once located to a point in time or a frequency, each cursor will remain there regardless of the timebase, time scale or DSO operating mode. This can be very useful if, for example, you locate to a particular position in a logic sequence (in LOGIC mode) and switch to the scope (ALT or CHOP mode) to see the analog signal in fine detail.
Voltage and Level Cursors
The DSO also provides VOLTAGE (waveform displays) and LEVEL (spectrum displays) cursors for precise measurement of voltages, voltage differences and spectrum levels. As with the <=X=> cursors, there are two <=Y=> cursors POINT and MARK which are manipulated in the same way.
The following screen shot shows the waveform <=Y=> cursors in use:
In this example (also from SYDNEY) the analog waveform on Channel A is 4.09V peak-to-peak starting from a negative voltage of -1.85V. The grey line in the middle is zero volts (ground).
It is important to understand that the <=Y=> cursors are associated with a channel and not the display itself. This is indicated with an underline below the channel's name.
By default the selected channel is CH A, but simply clicking on another channel name (eg, CH B) selects that channel instead.
The cursors move relative to the display. When a different channel is selected, the cursors may move to another position on the display if the newly selected channel's vertical scaling (V/Div) or offset is different from the previously selected channel. That is, the cursors retain the same voltage (or level) but the position on the display at which this voltage or level is located may be different.
Because the cursors report measured voltage on a channel, it is possible to make measurements on one channel and switch to the other channel to make measurements relative to the first channel.
Similarly, voltage difference measurements can be made very precisely by increasing the vertical sensitivity and adjusting the offset (if necessary) to place the MARK cursor and then again adjusting these controls appropriately to place the POINT cursor even if it is not possible to see both on the display at the same time for a given vertical scaling.
Slew Rate Example
A common use for combined cursor measurements is rise time or slew rate measurements.
Using the DSO's cursors together, such measurements are made easy:
In this example the waveform on channel A rises from -2.33V to 2.78V (a total of 5.11V) with the edge starting 29.5 uS after the trigger point rising for 296nS, giving a slew rate of 17.3 V per millsecond.
Mixed Signal Timing Example
Time cursors are extensively used with the mixed mode and logic analyser displays.
The trigger is shown in the center of the display.
The MARK cursor is placed at the start of the burst of edges on Bit 7 before the trigger.
The POINT cursor placed on the start of the next burst after the trigger, also on Bit 7.
Timing cursors are locked together between the analog and logic displays, so timing measurements may be made between analog and related logic events. In this case, Bit 7 is the most significant bit of a complex analog waveform which is the product of D/A convertion of the 8 logic signals.
The first burst (at the MARK) appears 11 uS before the trigger and the second appears 24 uS after the MARK (13 uS after the trigger). The frequency implied by the MARK to POINT period is 41.7kHz.