Manual adjustment significantly reduces skew between instruments and enhances synchronization repeatability, which results in greater coherence of multi-instrument measurements.
For background on manual adjustment, refer to
Manual Adjustment of
NI-TClk
Synchronization
.
Before beginning this procedure, complete the following:
-
Self-calibrate all instruments in your test system.
-
Obtain a reference signal with as low skew and jitter as possible.
Tip
The lower the skew and jitter of your reference signal, the better the synchronization you can achieve between instruments using manual adjustment.
This procedure applies to:
-
Manual adjustment of NI oscilloscopes that support
NI-TClk
synchronization
-
Synchronizing multiple NI oscilloscopes of a single bus type and model number (for example, all
PXI-5922
modules, but not
PXI-5922
and
PCI-5922
modules)
Complete the following steps to perform manual adjustment for your oscilloscopes.
Set Up
-
Connect the reference signal to all instruments you are synchronizing.
Tip
For best results, use cables of the same model and of identical length for each connection.
-
Configure an acquisition as appropriate for your reference signal.
-
Synchronize the instruments in your session using the
NI-TClk
API.
-
(LabVIEW,
LabVIEW NXG
only) Call
NI-SCOPE
Get Session Reference
to generate a reference from
NI-SCOPE
that
NI-TClk
can use.
-
Call
NI-TClk
Configure for Homogeneous Triggers.
-
Call
NI-TClk
Synchronize.
-
Call
NI-TClk
Initiate.
Calculate Adjustment
-
Fetch data from the instruments and measure the skew and jitter between the waveforms each instrument is acquiring, for example, by performing a point-by-point average.
-
Use any of the adjustment techniques applicable to your instrument to reduce the skew and jitter you measured:
Instrument |
Adjustment Technique |
Description |
When to Use |
-
PXIe/PXI/PCI-5105
-
PXIe/PXI/PCI-5114
-
PXIe/PXI/PCI-5122
-
PXI/PCI-5124
-
PXI/PCI-5142
-
PXI/PCI-5152
-
PXI/PCI-5153
-
PXI/PCI-5154
-
PXIe-5622
-
PXI/PCI-5922
|
NI-SCOPE
Adjust Sample Clock Relative Delay
function
|
Offsets the sample clock from the reference clock by the specified amount.
Reduces skew between instruments.
|
-
Adjustment range: ±1
Sample Clock Period
-
Adjustment unit: seconds
Tip
You can call this function multiple times to implement cumulative delay.
|
Primary technique for reducing skew and jitter for supported instruments.
[1]
|
-
PXIe-5110
-
PXIe-5111
-
PXIe-5113
-
PXIe-5163
-
PXIe-5164
-
PXIe-5170
-
PXIe-5171
-
PXIe-5172
|
NI-SCOPE
Absolute Sample Clock Offset
property
|
Offsets the sample clock from the reference clock by the specified amount.
Reduces skew between instruments and improves synchronization repeatability.
|
-
Adjustment range: ±0.5
Sample Clock Period
-
Adjustment unit: seconds
|
Primary technique for reducing skew and jitter for supported instruments.
|
All oscilloscopes that support
NI-TClk
synchronization except the following:
|
NI-TClk
Sample Clock Delay
property
|
Offsets the sample clock of an
NI-TClk
session relative to the other synchronized
NI-TClk
sessions.
Reduces skew between instruments.
-
Adjustment range: ±∞
-
Adjustment unit: seconds
|
To apply offset when adjustment beyond the range of other techniques is needed.
Sole technique for reducing skew for the
PXIe-5160
and
PXIe-5162.
|
-
Repeat
steps
4
and
5
until the measured skew and/or jitter are as low as possible.
Apply Adjustment
-
Depending on your adjustment technique(s) from
step
5
, save the adjustment you used to minimize skew and/or jitter.
Adjustment Technique |
Description |
NI-SCOPE
Adjust Sample Clock Relative Delay
|
The
NI-SCOPE
Oscillator Phase DAC Value
property converts the time offset you applied with
NI-SCOPE
Adjust Sample Clock Relative Delay
into a value that can apply the manual adjustment across sessions and improve synchronization repeatability.
-
Add the
NI-SCOPE
Oscillator Phase DAC Value
property to your program and read its value.
-
Save the
Oscillator Phase DAC Value
you read.
Note
You do not need to include the
NI-SCOPE
Adjust Sample Clock Relative Delay
function in your program after you have applied the adjustment with the
NI-SCOPE
Oscillator Phase DAC Value
property.
|
All other adjustment techniques
|
Save the value of each property. |
-
Write the saved value(s) of the property or properties you used prior to calling the
NI-TClk
Synchronize
function in other sessions when using the test system in an identical physical configuration.
Writing the manual adjustment property or properties to a session applies the improved synchronization to the session, regardless of the signals the test system is acquiring.
Reperform manual adjustment for all supported instruments in the following situations:
-
If any chassis, instruments, cables, or other physical components of your test system are moved, replaced, or removed
-
If the onboard temperature of any module in the test system changes by
±1° C
since the last self-calibration
-
If the trigger type, filtering characteristics, or any clocking parameters of your application are changed
Reperform manual adjustment for specific instruments in these additional situations:
-
PXIe-5185
and
PXIe-5186
only:
-
If any instrument is reset
-
If any instrument is self-calibrated
-
If the host computer or a chassis within the test system is rebooted
-
PXI-5922
and
PCI-5922
only: If any channel-based properties are changed