LIQUID INSTRUMENTS Moku Pro Frequency Response Analyzer User Manual
- October 30, 2023
- Liquid instruments
Table of Contents
Frequency Response Analyzer
Mukul: Pro User Manual
Moku Pro Frequency Response Analyzer
The Moku: Pro Frequency Response Analyzer can be used to measure a system’s
frequency response from 10 mHz to 300 MHz
Frequency response analyzers are commonly used to measure the transfer
functions of electrical, mechanical, or optical systems by injecting a swept
sine wave into the system and then comparing the output voltage to the input
voltage. The resulting measurements of the system’s magnitude and phase
response can be used to optimize the closed-loop response of control systems,
characterize resonant behavior in nonlinear systems, design filters, and
measure the bandwidth of different electronic or optical components. Frequency
response analyzers are an indispensable tool in any electronics and optics
lab.
Ensure Moku:Pro is fully updated. For the latest information, visit: liquidinstruments.com
User interface
| ID | Description | ID | Description |
|---|---|---|---|
| 1 | Main menu | 8 | Normalization tool |
| 2 | Back to instrument selection screen | 9 | Sweep mode |
| 3 | Export data | 10 | Start / pause sweep |
| 4 | Instrument configuration menu | 11 | Cursors |
| 5 | Channel settings | 12 | Phase plot |
| 6 | Swept sine output settings | 13 | Magnitude plot |
| 7 | Advanced demodulation settings |
Main menu
The main menu can be accessed by pressing the icon, allowing you to:
Preferences
You can access the preferences pane via the main menu. Here, you can reassign the color representations for each channel, connect to Dropbox, and more. Throughout the manual, the default colors (shown in the figure below) are used to present instrument features.
| ID | Description |
|---|---|
| 1 | Tap to change the color associated with Input Channels. |
| 2 | Tap to change the color associated with Output Channels. |
| 3 | Tap to change the color associated with Math Channel. |
| 4 | Indicate touch points on the screen with circles. This can be useful for |
demonstrations.
5| Change the currently linked Dropbox account to which data can be uploaded.
6| Notify when a new version of the app is available.
7| Moku: Pro automatically saves instrument settings when exiting the app, and
restores them again at launch. When disabled, all settings will be reset to
defaults on launch.
8| Moku: Pro can remember the last used instrument and automatically reconnect
to it at launch.
When disabled, you will need to manually connect every time.
9| Reset all instruments to their default state.
10| Save and apply settings.
Instrument configuration
The instrument configuration menu allows you to configure the Frequency
Response Analyzer for your measurement, which will vary depending on the
characteristics of the system under test.
Access the instrument configuration menu by pressing the icon.
Channels
Additional settings can be accessed by scrolling up and down.
| ID | Description | ID | Description |
|---|---|---|---|
| 1 | Select the measurement mode | 7 | Swept sine amplitude |
| 2 | Toggle channel on/off | 8 | Swept sine offset |
| 3 | Select AC or DC coupling | 9 | Turn on/off amplitude and/or offset |
| 4 | Select 1 MW or 50 W input impedance | 10 | Access additional settings |
| 5 | Select input range 400 mV, 4 V or 40 V peak-to-peak | 11 | Enable/disable |
Math Channel
6| Select 1 MW or 50 W output load| | Unwrap/wrap phase
Measurement mode
The frequency response can be displayed in Input (dBm, dBVpp, dBV ms), In ÷
Out (dB), and In ÷ In1 (dB) mode. In the Input mode, the amplitude response is
displayed as the measured power,
irrespective of the output amplitude. The In ÷ Out (dB) displays the response
as the input power ÷ output power in db. The In ÷ In1 (dB) allows the user to
dynamic measure the amplitude of swept sine wave via Input 1 and calculate the
relative amplitude response with respect to the measured amplitude from Input
Math channel
-
Select between addition, subtraction, multiplication, and division of two channels.
Additionally, you can create arbitrary complex-valued equations of the four channels. -
Compare transfer functions of channel 1, 2, 3, and 4 by configuring them identically.
Unwrap phase
- Phase is measured as a modulo of 2p. Enable unwrapping to display an estimate of the total accumulated phase of the system.
Swept sine
| ID | Description | ID | Description |
|---|---|---|---|
| 1 | Lock frequency axis | 7 | Configure minimum averaging time |
| 2 | Configure sweep start frequency | 8 | Configure minimum averaging cycles |
| 3 | Configure sweep stop frequency | 9 | Configure minimum settling time |
| 4 | Sel Select Linear or Log scale | 10 | Configure minimum setting cycles |
| 5 | Select number of sweep points | 11 | Total sweep time based upon selected |
parameters
6| Reverse direction of sweep| |
Sweep points
- Increasing the number of points in the sweep increases frequency resolution of the measurement, allowing narrower features to be detected over a wider frequency range, but will increase the total measurement duration.
Sweep scale
- Select whether or not the discrete points in the swept sine output are spaced linearly or logarithmically. Logarithmic sweeps provide greater measurement resolution at lower frequencies.
Averaging
- Measurements at each point in the frequency sweep are averaged to improve accuracy and precision. You can configure the period over which each measurement is averaged in order to control signal-to-noise ratio. Longer averaging times result in higher SNRs, allowing small features to be detected with greater precision. Shorter averaging times result in lower SNR measurements but the reduce total sweep time.
- The total averaging time is determined based on the minimum duration and minimum number of cycles over which each point in the sweep is averaged. The Moku: Pro Frequency Response Analyzer averages for the greater of the two values rounded up to the nearest number of integer cycles in order to avoid spectral leakage.
Settling time
- The settling time determines how long the Frequency Response Analyzer waits before performing measurements at each frequency in the sweep. Settling time is important when characterizing resonant systems with high Q-factors in order to allow excitations to settle between measurements. It can also be used to account for transmission delays in cables. When interrogating a non-resonant system, the settling time should be set to equal the total propagation delay through the system.
- The total settling time is determined based on the minimum duration and minimum number of cycles over which the instrument will wait before beginning a measurement at each frequency in the sweep. The Frequency Response Analyzer will wait for the greater effective duration of the two settings before beginning a measurement at each point in the sweep.
Advanced
| ID | Description |
|---|---|
| 1 | Enable/disable dynamic amplitude scaling |
| 2 | Adjust output phase for each channel |
| 3 | Select a harmonic to measure the frequency response of the swept sine |
Dynamic amplitude
Enabling dynamic amplitude maximizes the dynamic range of the measurement by
automatically reducing the output signal amplitude when saturation is detected
on the corresponding input channel. This can be very useful when measuring
devices whose amplitude response varies strongly with frequency, making it
difficult to measure the frequency response with high dynamic range using a
constant driving source.
Additionally, the user interface provides a momentary pop-up message warning
when input saturation is detected.
Clicking the orange exclamation icon on the right-hand side of the graph will provide additional information regarding which frequencies are saturated and possible solutions, including enabling dynamic amplitude mode.
Cursors
Magnitude and phase cursors can be added to the Frequency Response plot by pressing the button.
Tip: Magnitude and phase cursors can be moved between the two plots by dragging them vertically across the horizontal divider.
| ID | Cursor item | Description |
|---|---|---|
| 1 | Frequency cursor | Drag to adjust frequency, tap and hold to hide channel. |
| 2 | Amplitude cursor | Drag to adjust tap to set magnitude manually and other |
options.
3| Create cursor| Tap to create, or drag up or drag right for
magnitude/frequency cursor.
4| Phase cursor| Drag to adjust, tap to set phase manually and other options.
5| Cursor label| Label depicting frequency, amplitude, and phase of cursor.
Drag to adjust. Tap to manually adjust or remove.
| ID | Description | ID | Description |
|---|---|---|---|
| 1 | Cursor action buttons | 4 | Add phase cursor |
| 2 | Remove all cursors | 5 | Add magnitude cursor |
| 3 | Add frequency cursor |
Magnitude cursors
Magnitude cursors can be added to the magnitude plot by tapping the
icon and selecting “Add magnitude
cursor.” A magnitude cursor can also be created by dragging your finger up
from the cursor icon and then repositioning it on the magnitude plot.
Phase cursors
Phase cursors can be added to the phase plot by tapping the
icon and selecting “Add phase
cursor.” A phase cursor can also be created by dragging your finger up from
the cursor icon and then repositioning it on the phase plot.
Frequency cursors
Up to five frequency cursors can be added to the frequency plot by tapping the
icon and selecting “Add frequency
cursor.” Frequency cursors can also be created by dragging your finger to the
right from the cursor icon.
Removing cursors
All active cursors can be removed from the frequency and phase plots by
tapping the 
icon and
selecting “Remove all cursors.” Individual cursors can be removed by tapping
their label and pressing “Remove.”
Sweep modes
Single
Tapping the icon will enable single sweep mode, which will pause the swept
sine source at the end of the next full sweep. The swept sine signal will be
turned off after the sweep completes and displayed data will not be updated.
Continuous
Tapping the icon will enable continuous sweep mode, which will perform a new
measurement as soon as the previous one has finished. This mode is commonly
used to monitor systems with transfer functions that may change over time
(e.g., control loops).
Pause / Restart
Tapping the icon will immediately pause the current sweep. While paused, you
can zoom in on features for more details, but no new data will be captured.
Pressing the icon will also pause capture.
Tapping the or icons will restart the sweep.
| ID | Description | ID | Description |
|---|---|---|---|
| 1 | Start single sweep | 2 | Stop sweep |
Normalization
The Moku: Pro Frequency Response Analyzer features a normalization tool that can be used to normalize subsequent measurements. Normalization is useful when compensating for cable delays and comparing different devices under test.
| ID | Description | ID | Description |
|---|---|---|---|
| 1 | Normalize menu | 3 | Remove normalization |
| 2 | Re-normalize |
Tapping the icon will bring up the normalization menu. Re-normalize will replace the current normalization trace with a new one. Remove normalization will erase all stored normalization settings and cannot be undone.
Exporting data
Measurement traces and screenshots can be uploaded to My Files (iOS 11 or
later), Dropbox, email, iCloud, or Clipboard (screenshot is not copied to the
clipboard).
The Frequency Response Analyzer instrument settings can also be exported for
future reference.
To export a measurement trace, press the icon at the top of the frequency
response plot.
| ID | Button | Description |
|---|---|---|
| 1 | Traces data | Select to enable saving of trace data |
| 2 | Traces format | Tap to select CSV or MATLAB format |
| 3 | Settings data | Select to save instrument settings |
| 4 | Screenshot capture | Select to capture screenshot |
| 5 | Screenshot format | Tap to select JPG or PNG screenshot format |
| 6 | Saved data destination | Select data destination |
Ensure Moku: Pro is fully updated. For the latest information, visit: liquidinstruments.com
Moku: Pro Frequency Response Analyzer User Manual
© 2023 Liquid Instruments. All rights reserved.
Documents / Resources
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LIQUID INSTRUMENTS Moku Pro Frequency Response
Analyzer
[pdf] User Manual
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References
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