Scope Module¶
The Scope Module corresponds to the functionality available in the Scope tab in the LabOne User Interface and provides API users with an interface to acquire assembled and scaled scope data from the instrument programmatically.
Introduction to Scope Data Transfer¶
In general, an instrument's scope can generate a large amount of data which requires special treatment by the instrument's firmware, the Data Server, LabOne API and API client in order to process it correctly and efficiently. The Scope Module was introduced in LabOne 16.12 to simplify scope data acquisition for the user. This section provides a top-level overview of how scope data can be acquired and define the terminology used in subsequent sections before looking at the special and more simplified case when the Scope Module is used.
There are three methods of obtaining scope data from the device:
- By subscribing directly to the instrument node
/DEV..../SCOPES/n/WAVEand using thepoll()command. This refers to the lower-level interface provided by theziDAQServerclasssubscribe()andpoll()commands. - By subscribing to the instrument node
/DEV..../SCOPES/n/WAVEin the Scope Module and using the Scope Module'sread()command. - By subscribing to the instrument's scope streaming node
/DEV..../SCOPES/n/STREAM/SAMPLEwhich continuously streams scope data as a block stream. This is only available on MF and UHF instruments with the DIG Option enabled. The Scope Module does not support acquisition from the scope streaming node.
Segmented Mode
Additionally, MF and UHF instruments which have the DIG option enabled
can optionally record data in "segmented" mode which allows back-to-back
measurements with very small hold-off times between measurements.
Segmented mode enables the user to make a fixed number of measurements
(the segments), which are stored completely in the memory of the
instrument, before they are transferred to the Data Server (this
overcomes the data transfer rate limitation of the device's connected
physical interface, e.g., USB or 1GbE for a fixed number of
measurements). The advantage to this mode is precisely that the hold-off
time, i.e. the delay between two measurements, can be very low. Data
recorded in segmented mode is still available from the instrument node
/DEV..../SCOPES/n/WAVE as for non-segmented data, but requires an
additional reshaping described in
Segmented Recording.
Scope Data Nomenclature¶
We'll use the following terminology to describe the scope data streamed from the device:
Wave
The name of the leaf (/DEV..../SCOPES/n/WAVE) in the device node tree
that contains scope data pushed from the instrument's firmware to the
Data Server. The data structure returned by this node is defined by
the API Level of the connected session. It is also the name of the
structure member in scope data structures that holds the actual scope
data samples.
Record
Refers to one complete scope data element returned by the Scope Module. It may consist of one or multiple segments.
Segment
A segment is a completely assembled and scaled wave. If the instrument's scope is used in segmented mode, each record will consist of multiple segments. If not used in segmented mode, each record comprises of a single segment and the terms record and segment can be used interchangeably.
Block
When the length of data (/DEV..../SCOPES/n/LENGTH) in a scope segment
is very large the segment returned by the device node
(/DEV..../SCOPES/n/WAVE) is split into multiple blocks. When using the
poll/subscribe method the user must assemble these blocks; the Scope
Module assembles them for the user into complete segments.
Shot
The term shot is often used when discussing data acquired from laboratory oscilloscopes, we try to avoid it in the following in order to more easily distinguish between records and segments when recording in segmented mode.
Advantages of the Scope Module¶
Although it is possible to acquire scope data using the lower-level subscribe/poll method, the Scope Module provides API users with several advantages. Specifically, the Scope Module:
- Provides a uniform interface to acquire scope data from all instrument classes (HF2 scope usage differs from and MF and UHF devices, especially with regards to scaling).
- Scales and offsets the scope wave data to get physically meaningful values. If data is polled from the device node using subscribe/poll the scaling and offset must be applied manually.
- Assembles large multi-block transferred scope data into single complete records. When the scope is configured to record large scope lengths and data is directly polled from the device node
/DEV.../SCOPES/n/WAVEthe data is split into multiple blocks for efficient transfer of data from the Data Server to the API; these must then be programmatically reassembled. The Scope Module performs this assembly and returns complete scope records (unless used in pass-through mode,mode=0). - Can be configured to return the FFT of the acquired scope records (with
mode=3) as provided by the Scope Tab in the LabOne UI. FFT data is not available from the device nodes in the/DEV/..../SCOPES/branch using subscribe/poll. - Can be configured to average the acquired scope records using the
averager/parameters. - Can be configured to return a specific number of scope records using the
historylengthparameter.
Working with Scope Module¶
It is important to note that the instrument's scope is implemented in
the firmware of the instrument itself and most of the parameters
relevant to scope data recording are configured as device nodes under
the /DEV.../SCOPES/ branch. Please refer to the instrument-specific User
Manual for a description of the Scope functionality and a list of the
available nodes.
The Scope Module does not modify the instrument's scope configuration
and, as such, processes the data arriving from the instrument in a
somewhat passive manner. The Scope Module simply reassembles data
transferred in multiple blocks into complete segments (so that they
consist of the configured /DEV..../SCOPES/n/LENGTH) and applies the
offset and scaling required to get physically meaningful values to the
(integer) data sent by the instrument.
The following steps should be used as a guideline for a Scope Module work-flow:
-
Create an instance of the Scope Module. This instance may be re-used for recording data with different instrument settings or Scope Module configurations.
-
Subscribe in the Scope Module to the scope's streaming block node (
/DEV..../SCOPES/n/WAVE) to specify which device and scope to acquire data from. Data will only be acquired after enabling the scope and calling Scope Moduleexecute(). -
Configure the instrument ready for the experiment. When acquiring data from the signal inputs it is important to specify an appropriate value for the input range (
/DEV..../SIGINS/n/RANGE) to obtain the best bit resolution in the scope. The signal input range on MF and UHF instruments can be adjusted automatically, see the/DEV..../SIGINS/n/AUTORANGEnode and API utility functions demonstrating its use (e.g.,zhinst.utils.sigin_autorange()in the LabOne Python API). Configure the instrument's scope as required for the measurement. If recording signals other than hardware channel signals (such as a PID's error or a demodulator R output), be sure to configure the nodes/DEV..../SCOPES/n/CHANNELS/n/LIMITLOWERand/DEV..../SCOPES/n/CHANNELS/n/LIMITUPPERaccordingly to obtain the best bit resolution in the scope. -
Configure the Scope Module's parameters as required, in particular: (a) Set
modein order to specify whether to return time or frequency domain data. See Scope Module Modes for more information on the Scope Module's modes. (b) Set thehistorylengthparameter to tell the Scope Module to only return a certain number of records. Note, as the Scope Module is acquiring data therecordsoutput parameter may grow larger thanhistorylength; the Scope Module will return the last number of records acquired. (c) Set theaveragerparameters to select the averaging method and enable averaging of scope records, see Averaging. -
Enable the scope (if not previously enabled) and call Scope Module
execute()to start acquiring data. -
Wait for the Scope Module to acquire the specified number of records. Note, if certain scope parameters are modified during recording, the history of the Scope Module will be cleared; see Scope Parameters that reset the Scope Module for the list of parameters that trigger a Scope Module reset.
-
Call Scope Module
read()to transfer data from the Module to the client. Data may be read out usingread()before acquisition is complete (advanced use). Note, an intermediate read will create a copy in the client of the incomplete record which could be critical for memory consumption in the case of very long scope lengths or high segment counts. The data structure returned byread()is of typeZIScopeWaveEx. -
Check the flags of each record indicating whether any problems occurred during acquisition.
-
Extract the data for each recorded scope channel and, if recording data in segmented mode, reshape the wave data to allow easier access to multi-segment records (see Segmented Recording) Note, the scope data structure only returns data for enabled scope channels.
Data Acquisition and Transfer Speed
It is important to note that the time to transfer long scope segments from the device to the Data Server can be much longer than the duration of the scope record itself. This is not due to the Scope Module but rather due to the limitation of the physical interface that the device is connected on (USB, 1GbE). Please ensure that the PC being used has adequate memory to hold the scope records.
Scope Module Modes¶
The mode is applied for all scope channels returned by the Scope
Module. Although it is not possible to return both time and frequency
domain data in one instance of the Scope Module, multiple instances may
be used to obtain both.
The Scope Module does not return an array consisting of the points in
time (time mode) or frequencies (FFT mode) corresponding to the samples in
ZIScopeWaveEx. These can be constructed as
arrays of N points, where N is the scope length configured through the node /DEV.../SCOPES/n/LENGTH spanning the intervals:
Time mode
[0, dt*totalsamples], where dt and totalsamples are numeric fields in ZIScopeWaveEx.
In order to get a time array relative to the trigger position, (timestamp - triggertimestamp)/float(clockbase) must be subtracted from the times
in the interval, where timestamp and triggerstamp are fields inZIScopeWaveEx
FFT mode
[0, (clockbase/2^scope_time)/2], where scope_time is the value of the device node /DEV..../SCOPES/n/TIME and clockbase is the value of /DEV..../CLOCKBASE.
Averaging¶
The Scope Module of LabOne offers an averaging feature to improve the signal-to-noise ratio (SNR) of the acquired signals by reducing the noise through averaging over multiple scope segments. The averaging engine starts by setting the module node averager/enable to 1. The module offers two averaging methods, namely Uniform and Exponential, which can be selected through averager/method. The uniform averaging implements the following recursive expression:
where \(x[n]\) is the \(n\)-th acquired scope segment, and \(y[n]\) is the averaged signal after \(n\) scope segments. The exponential averaging is based on the following recursive equation:
in which \(w\) is the weight of exponential averaging and can be adjusted through the node averager/weight. The weight corresponds to the number of segments to achieve 63% settling; doubling the value of weight achieves 86% settling.
If the scope is in single acquisition mode, no averaging is performed. To obtain the number of segments that have been averaged, one can query the read-only node averager/count. The average calculation can be restarted by setting averager/restart to 1. This node will be automatically set to 0 when averaging starts.
It is important to note that the averaging functionality is performed by the Scope Module on the PC where the API client runs, not on the device. Enabling averaging does not mean that less data is sent from the instrument to the Data Server.
Segmented Recording¶
When the instrument's scope runs segmented mode the wave structure
member in the ZIScopeWaveEx is an array
consisting of length*segment_count where length is the value of
/DEV..../SCOPES/0/LENGTH and num_segments is
/DEV..../SCOPES/n/SEGMENTS/COUNT. This is equal to the value of the
totalsamples structure member.
The Scope Module's progress() method can be used to check the progress
of the acquisition of a single segmented recording. It is possible to
read out intermediate data before the segmented recording has finished.
This will however, perform a copy of the data; the user should ensure
that adequate memory is available.
If the segment count in the instrument's scope is changed, the Scope Module must be re-executed. It is not possible to read multiple records consisting of different numbers of segments within one Scope Module execution.
Scope Parameters that reset the Scope Module¶
The Scope Module parameter records and progress() are reset and all
records are cleared from the Scope Module's history when the following
critical instrument scope settings are changed:
/DEV.../SCOPES/n/LENGTH/DEV.../SCOPES/n/RATE/DEV.../SCOPES/n/CHANNEL/DEV..../SCOPES/n/SEGMENTS/COUNT/DEV..../SCOPES/n/SEGMENTS/ENABLE
Scope Module Use on HF2 Instruments¶
The HF2 scope is supported by the Scope Module, in which case the API
connects to the HF2 Data Server using API Level 1
(the HF2 Data Server does not support higher levels). When using the
Scope Module with HF2 Instruments the parameter externalscaling must
be additionally configured based on the currently configured scope
signal's input/output hardware range, see the /externalscaling node for more details.
This is not necessary for other instrument classes.
Node Documentation¶
This section describes all the nodes in the Scope Module node tree organized by branch.
averager¶
/averager/count ¶
| Properties: | Read |
| Type: | Integer (64 bit) |
| Unit: | None |
Indicates the number of scope shots that have been averaged.
/averager/enable ¶
| Properties: | Read, Write |
| Type: | Integer (64 bit) |
| Unit: | None |
Enable averaging. = 0: Averaging disabled. 1: Averaging enabled, updating last history entry, using the method set by averager/method.
/averager/method ¶
| Properties: | Read, Write |
| Type: | Integer (enumerated) |
| Unit: | None |
Specify the averaging method.
| Value | Description |
|---|---|
| 0 | "exponential": Exponential moving average |
| 1 | "uniform": Uniform averaging |
/averager/resamplingmode ¶
| Properties: | Read, Write |
| Type: | Integer (enumerated) |
| Unit: | None |
Specify the resampling mode. When averaging scope data recorded at a low sampling rate that is aligned by a high resolution trigger, scope data must be resampled to keep the corresponding samples between averaged recordings aligned correctly in time relative to the trigger time.
| Value | Description |
|---|---|
| 0 | "linear": Linear interpolation |
| 1 | "pchip": PCHIP interpolation |
/averager/restart ¶
| Properties: | Read, Write |
| Type: | Integer (64 bit) |
| Unit: | None |
Set to 1 to reset the averager. The module sets averager/restart back to 0 automatically.
/averager/weight ¶
| Properties: | Read, Write |
| Type: | Integer (64 bit) |
| Unit: | None |
Specify the averaging weight of the exponential averaging method. It is not used by the uniform averaging method. Weight values 0 and 1 correspond to no averaging.
clearhistory¶
/clearhistory ¶
| Properties: | Read, Write |
| Type: | Integer (64 bit) |
| Unit: | None |
Remove all records from the history list.
error¶
/error ¶
| Properties: | Read |
| Type: | Integer (64 bit) |
| Unit: | None |
Indicates whether an error occurred whilst processing the current scope record; set to non-zero when a scope flag indicates an error. The value indicates the accumulated error for all the processed segments in the current record and is reset for every new incoming scope record. It corresponds to the status LED in the LabOne User Interface's Scope tab - API users are recommended to use the flags structure member in ZIScopeWaveEx instead of this output parameter.
externalscaling¶
/externalscaling ¶
| Properties: | Read, Write |
| Type: | Double |
| Unit: | None |
Scaling to apply to the scope data transferred over API level 1 connection. Only relevant for HF2 Instruments.
fft¶
/fft/power ¶
| Properties: | Read, Write |
| Type: | Integer (64 bit) |
| Unit: | None |
Enable calculation of the power value.
/fft/powercompensation ¶
| Properties: | Read, Write |
| Type: | Integer (64 bit) |
| Unit: | None |
Apply power correction to the spectrum to compensate for the shift that the window function causes.
/fft/spectraldensity ¶
| Properties: | Read, Write |
| Type: | Integer (64 bit) |
| Unit: | None |
Enable calculation of the spectral density value.
/fft/window ¶
| Properties: | Read, Write |
| Type: | Integer (enumerated) |
| Unit: | None |
FFT Window
| Value | Description |
|---|---|
| 0 | "rectangular": Rectangular |
| 1 | "hann": Hann (default) |
| 2 | "hamming": Hamming |
| 3 | "blackman_harris": Blackman Harris |
| 16 | "exponential": Exponential (ring-down) |
| 17 | "cos": Cosine (ring-down) |
| 18 | "cos_squared": Cosine squared (ring-down) |
historylength¶
/historylength ¶
| Properties: | Read, Write |
| Type: | Integer (64 bit) |
| Unit: | None |
Maximum number of entries stored in the measurement history.
lastreplace¶
/lastreplace ¶
| Properties: | Read, Write |
| Type: | Integer (64 bit) |
| Unit: | None |
Reserved for LabOne User Interface use.
mode¶
/mode ¶
| Properties: | Read, Write |
| Type: | Integer (enumerated) |
| Unit: | None |
The Scope Module's data processing mode.
| Value | Description |
|---|---|
| 0 | "passthrough": Passthrough: scope segments assembled and returned unprocessed, non-interleaved. |
| 1 | "exp_moving_average": Cumulative averaging: entire scope recording assembled, scaling applied, averaging if enabled (see averager/enable) using method set by averager/method, data returned in float non-interleaved format. |
| 2 | Reserved for future use (average n segments). |
| 3 | "fft": FFT, same as mode 1, except an FFT is applied to every segment of the scope recording before averaging. See the fft/* parameters for FFT parameters. |
records¶
/records ¶
| Properties: | Read |
| Type: | Integer (64 bit) |
| Unit: | None |
The number of scope records that have been processed by the Scope Module since execute() was called or a critical scope setting has been modified (see manual for a list of scope settings that trigger a reset).
save¶
/save/csvlocale ¶
| Properties: | Read, Write |
| Type: | String |
| Unit: | None |
The locale to use for the decimal point character and digit grouping character for numerical values in CSV files: "C": Dot for the decimal point and no digit grouping (default); "" (empty string): Use the symbols set in the language and region settings of the computer.
/save/csvseparator ¶
| Properties: | Read, Write |
| Type: | String |
| Unit: | None |
The character to use as CSV separator when saving files in this format.
/save/directory ¶
| Properties: | Read, Write |
| Type: | String |
| Unit: | None |
The base directory where files are saved.
/save/fileformat ¶
| Properties: | Read, Write |
| Type: | Integer (enumerated) |
| Unit: | None |
The format of the file for saving data.
| Value | Description |
|---|---|
| 0 | "mat": MATLAB |
| 1 | "csv": CSV |
| 2 | "zview": ZView (Impedance data only) |
| 3 | "sxm": SXM (Image format) |
| 4 | "hdf5": HDF5 |
/save/filename ¶
| Properties: | Read, Write |
| Type: | String |
| Unit: | None |
Defines the sub-directory where files are saved. The actual sub-directory has this name with a sequence count (per save) appended, e.g. daq_000.
/save/save ¶
| Properties: | Read, Write |
| Type: | Integer (64 bit) |
| Unit: | None |
Initiate the saving of data to file. The saving is done in the background. When the save has finished, the module resets this parameter to 0.
/save/saveonread ¶
| Properties: | Read, Write |
| Type: | Integer (64 bit) |
| Unit: | None |
Automatically save the data to file immediately before reading out the data from the module using the read() command. Set this parameter to 1 if you want to save data to file when running the module continuously and performing intermediate reads.