examples: Speed up voltage_acq_clk_plot_wfm.py and handle multiple channels correctly

[bkeryan]

• This contribution adheres to CONTRIBUTING.md.
• I've updated CHANGELOG.md if applicable.
• I've added tests applicable for this pull request

What does this Pull Request accomplish?

Speed up voltage_acq_clk_plot_wfm.py by calculating the time data using np.linspace instead of waveform.timing.get_timestamps(). get_timestamps() currently creates a list of datetime objects, which is very slow for large sample counts.

Update voltage_acq_clk_plot_wfm.py to support multiple channels correctly:

• Use the minimum start time to get the time offset for each channel. This compensates for the skew introduced by the AI Convert Clock on multiplexed devices.
• Display the channel names in the plot legend rather than the plot title.

Why should this Pull Request be merged?

Closes #936

Demonstrates how to plot multiple waveforms.

What testing has been done?

Manual testing

Measured performance using PowerShell Measure-Command

[bkeryan]

Example output with a floating signal:

[github-actions]

Test Results

    48 files  ±0      48 suites  ±0   1h 16m 40s ⏱️ -30s
 3 209 tests ±0   2 556 ✅ ±0     653 💤 ±0  0 ❌ ±0 
62 228 runs  ±0  49 398 ✅ ±0  12 830 💤 ±0  0 ❌ ±0 

Results for commit 5244f7a. ± Comparison against base commit 960e35b.

♻️ This comment has been updated with latest results.

[bkeryan]

Example output with AO loopback channels, 250 kS/s, 250k samples

[bkeryan]

Example of calculated time_offset:

0.0
7.629394531e-06
2.2888183594e-05
3.8146972656e-05

Note that it currently calculates time_offset=0.0 for high AI Convert Clock rates. There is already an internal bug for this, but I also filed #941 for visibility.

[bkeryan]

I ran PowerShell Measure-Command with the following changes, like in #936

diff --git a/examples/analog_in/voltage_acq_int_clk_plot_wfm.py b/examples/analog_in/voltage_acq_int_clk_plot_wfm.py
index bf59a795..9ff8dd90 100644
--- a/examples/analog_in/voltage_acq_int_clk_plot_wfm.py
+++ b/examples/analog_in/voltage_acq_int_clk_plot_wfm.py
@@ -29,7 +29,7 @@ def plot_analog_waveform(

 with nidaqmx.Task() as task:
     task.ai_channels.add_ai_voltage_chan("Dev1/ai0")
-    task.timing.cfg_samp_clk_timing(1000.0, sample_mode=AcquisitionType.FINITE, samps_per_chan=50)
+    task.timing.cfg_samp_clk_timing(1e6, sample_mode=AcquisitionType.FINITE, samps_per_chan=100_000)

     waveforms = task.read_waveform(READ_ALL_AVAILABLE)
     if not isinstance(waveforms, list):
@@ -44,4 +44,4 @@ with nidaqmx.Task() as task:
     plot.legend()
     plot.grid(True)

-    plot.show()
+    plot.show(block=False)

PS D:\dev\nidaqmx-python\examples\analog_in> Measure-Command { poetry run python voltage_acq_int_clk_plot_wfm.py }


Days              : 0
Hours             : 0
Minutes           : 0
Seconds           : 2
Milliseconds      : 523
Ticks             : 25239501
TotalDays         : 2.92123854166667E-05
TotalHours        : 0.00070109725
TotalMinutes      : 0.042065835
TotalSeconds      : 2.5239501
TotalMilliseconds : 2523.9501

This is about the same as voltage_acq_int_clk_plot_data.py.

[bkeryan]

Example output with a floating signal:

With endpoint=False, the Y-axis shows "0.05" but the data ends at 0.049.