NVGate Output Signals

This module generates multiple signals such as fixed sinus, random noises, and swept sinus.

Sine

Used to generate and configure up to 6 fixed sinus. A sinusoidal signal is generated with the frequency specified in the sine Frequency field. The frequency corresponds to one of the analysis bands. This type of signal is used for measuring the amount of distortion in a system, for example. The amplitude of the signal can be changed using the Level settings.

Frequency: sine frequency can be 0 for DC generation.

• Peak level: the peak level
• RMS level: sine RMS level. This setting can be displayed in dB.

Note: Amplitude and frequency modifications are applied immediately without any transition.

Multi-sine

Multisine is computed by adding sine signals whose frequencies are power of two sub-modules of sampling frequency. This means that multisine output block includes all discrete sine waves of FFT spectrum of corresponding block size and resolution. Multisine has the advantage of showing no leakage effect in FFT as all sine waves are exact periods of the trigger block for FFT computation. The most appropriate FFT weighting window to be used is “uniform” window. Multisine generators work on a sample block basis, it means signal blocks are repeated identically over time.

Used to generate and configure up to 2 multi-sines. The multi-sine is computed by adding sine signals whose frequencies are power of two sub-modules of sampling frequency. So with the FFT analyzer, each sine signal can be exactly at an analysis frequency line and there is no leakage due to analysis window. Due to its specific structure, using a rectangular analysis window for FFT analysis on a multi-sine excitation is recommended.

The phase between sine signals can be controlled in order to get a low crest factor or randomized, but with a higher crest factor.

Multi-sine is periodic with a period equal to the opposite of its frequency resolution.

• Lower frequency: the lower frequency of the multi-sine frequency range. Its minimum value is the resolution.
• Upper frequency: the upper frequency of the multi-sine frequency range. Its maximum value is SF / 2.56, where SF is the sampling frequency.
• RMS level: multi-sine RMS level. This setting can be displayed in dB.
• Resolution: the resolution of the multi-sine. Its minimum value is SF / 16384, where SF is the sampling frequency. Its maximum value is SF / 256.
• Phase: Computational mode of the original sinusoid phases.

Phase	Description
Random	The original phase of each sinusoid is selected randomly after each multi sine deactivation/activation. First activation: After reactivation: Phase relationship between sine waves is selected at selection of setting and will not change unless “random” setting is changed back and forward. After “random” is selected phase relationship is defined (randomly for the first block) and repeated identically for each signal block of N lines. Phase relationship for all multisine generators will be different as random setting activation is made at different moment in time and applied for different generator objects. Two blocks of multisine random phase of the same generator are 100% correlated. Two mulitsine random phase generators are not correlated.
Fixed	Each sinusoid has the same original phase even after multi sine deactivation/activation. Multisine phase relation if fixed and will be the same each time setting “fixed” is selected. Phase relationship is the same for all multisine generators meaning that signal blocks will be the identical between any multisine generators of the same setting. Multisine fixed phase generators are 100% correlated.

Burst setting in Multisine generators will shorten time during which output signal is active despite signal block being of the same length. All bandwidth frequencies are present in each burst but may not be complete cycles as block period is truncated. Two bursts being identical (respectively fixed or random phase) they are 100% correlated. Two burst random from two separate generators will not be correlated signals.

Random noise

Used to generate and configure up to 2 white or pink random noise types.

Signal block is recalculated each time. All frequencies of generator bandwidth are taken into account with a resolution of Fs/16384 (Fs being front end sampling frequency), this resolution is independent from FFT resolution. Consequently signal content of each FFT trigger block is not the same meaning that signals between two trigger blocks are not correlated. Similarly random noise signal between two separate generators are also not correlated.

Random noise is generated using algorithms that guarantee no short or long-term periodicity.

• Lower frequency: the lower frequency of the Random noise frequency range. Its minimum value is equal to SF / (2.56 * 6400), where SF is the sampling frequency and 6400 + 1 is the resolution.
• Upper frequency: the upper frequency of the Random noise frequency range. Its maximum value is SF / 2.56, where SF is the sampling frequency.
• RMS level: the Random noise RMS level. This setting can be displayed in dB.
• Period: The period selected for the Random noise. It used to define a Random Block. Its maximum value is 100ms.
• Burst: This setting lets the user specify the percentage of non-null signal in a random block.

• Type:

Type	Description
White	White noise has the same distribution of power for all frequencies, so there is the same amount of power between 0 and 500 Hz, 500 and 1,000 Hz or 20,000 and 20,500 Hz.
Pink	Pink noise has the same distribution of power for each octave, so the power between 0.5 Hz and 1 Hz is the same as between 5,000 Hz and 10,000 Hz. Since power is proportional to amplitude squared, the energy per Hz will decline at higher frequencies at the rate of -10dB/decade.

Chirp

Used to generate and configure up to 6 chirps. A sine signal, of which the frequency varies from Lower Frequency to Upper Frequency, is generated in the delay corresponding to the size of a generator block.

• Lower frequency: the lower frequency of the Random noise frequency range. Its minimum value is equal to SF / (2.56 * 6400), where SF is the sampling frequency and 6400 + 1 is the resolution.
• Upper frequency: the upper frequency of the chirp frequency range. Its maximum value is SF / 2.56, where SF is the sampling frequency.
• RMS level: the chirp RMS level. This setting can be displayed in dB.
• Size: This setting specifies the number of samples required for the generator to go from the lower frequency to the upper one.

Block size	FFT lines number
256	101
512	201
1024	401
2048	801
4096	1601
8192	3201
16384	6401

• Burst: This setting lets the user specify the percentage of non-null signal greater than the size of a generator block. For instance, for a burst value of 25% and a block size of 1024, the generator delivers blocks of 256 samples of chirp separated by blocks of 768 null samples.

Size = 256 Burst = 70

Advanced sine

Used to generate and configure up to 6 advanced sines, allowing the user to generate a swept sine, a pure tone, or to sweep step-by-step.

• Gain: Each advanced sine has a gain setting with a 0dB reference that is the value of the Advanced sine settings/ Peak level setting
• Phase offset: All the advanced sine have the same phase reference. This setting is used to set a phase offset between them.

Advanced sine settings

This sub-module contains the settings related to the main advanced sine generator, including the advanced sine mode setting, stabilization time, amplitude variation...

• Mode:

Mode	Description
Sweep:	The advanced sine performs a continuous sweep of the frequencies between Start Frequency and Stop Frequency
Step:	The advanced sine performs a sweep of the frequencies between Start Frequency and Stop Frequency, it stops at each step, waits during stabilization time, and waits for the new step event before going on.
Pure tone:	The advanced sine generates a pure sine with the frequency of the Advanced sine settings/ Target Frequency value

• Synchronization: "linked to run" or "Free run". The Advanced sine generator will not be stopped by a stop event, if the setting is on ’Free run’. The default value is ’Linked to run’.

If you change the amplitude or the frequency of the generated signal, there will be a stabilization time, and you will have to generate an event when the signal is stabilized.

In those 3 modes, each time the generator stops on a frequency;

1. at the beginning (amplitude increase until the first frequency),

2. at a new step (at the end of stabilization time), or in ’pure tone’ or ’swept sine’ pause mode when it reaches the target frequency; the generator send a stabilized event, after being stabilized (amplitude and frequency).

3. In ’Free run’, if the generator is already stabilized at the run event, then a stabilized event is generated at this moment.

If the output is on ’Advanced sine’ source, the setting of ’Synchronization’ of the advanced sine will recopied to the ’synchronization’ of the output (which one become fixed).

Hidden/fixed:

Mode	Sweep	Step	Pure tone
Synchronization	Fixed to ’Linked to run’	Visible	Visible

• Pause: On / Off. When Pause is active, the frequency sweeping is halted then there is only one frequency generated. This frequency is now called "Target frequency". You can modify this frequency value to another target to be reached so the frequency will sweep to this new target.

Hidden/fixed:

Mode	Sweep	Step	Pure tone
Pause	visible	hidden	hidden

• Peak level: the advanced sine peak level (between 0 and 10 V).
• Start frequency: The start frequency of the sweep.

Hidden/fixed:

Mode	Sweep	Step	Pure tone
Start frequency	visible	visible	hidden

• Stop frequency: The stop frequency of the sweep.

Hidden/fixed:

Mode	Sweep	Step	Pure tone
Stop frequency	visible	visible	hidden

• Target frequency: The value of this setting is the frequency currently generated when the value of the Pause setting is "On" or if the Mode is set to "Pure Tone"

Hidden/fixed:

Mode	Sweep	Step	Pure tone
Target frequency	visible if Pause = On	visible if Pause = On	visible

• Sweep variation: Two different types of sweep are available: a linear sweeping or a logarithmic sweep:

Sweep variation	Description
Lin	The Sweep speed is constant
Log	The Sweep speed increases exponentially when the frequency increase is linear

Hidden/fixed:

Mode	Sweep	Step	Pure tone
Sweep variation	visible	fixed to Lin	hidden

• Sweep speed: It is expressed in Hz/s in a linear sweep variation, and in dec/s in a logarithmic sweep variation.

Hidden/fixed:

Mode	Sweep	Step	Pure tone
Sweep speed	visible	hidden	hidden

• Sweep type:

Sweep type	Description
One shot	The advanced sine sweeps the frequencies from Start Frequency to Stop Frequency and stops.
One cycle	The advanced sine sweeps the frequencies from Start Frequency to Stop Frequency, then back to Start Frequency and stops.
Continuous	The advanced sine sweeps the frequencies between Start Frequency to Stop Frequency without stopping.

Hidden/fixed:

Mode	Sweep	Step	Pure tone
Sweep type	visible	visible	hidden

• Stabilization time: Sweep mode: Selects wait time for the advanced sine at the start frequency and at the right level before starting the sweep. Step mode: Selects wait time for the advanced sine at each step before waiting for the new step event.
• Amplitude 'variation': Maximum length of time for the advanced sine to reach a new level.
• Phase speed: Speed of phase variation when setting a new value for Advanced sine x/ Phase offset setting
• Step: Frequency gap between two steps

Hidden/fixed:

Mode	Sweep	Step	Pure tone
Sweep type	visible	visible	hidden

• New step: The event that triggers the sweep of the advanced sine to the next step

Hidden/fixed:

Mode	Sweep	Step	Pure tone
Sweep type	hidden	visible	hidden

Synchro

This special output signal is used to synchronize raw data recorded on multiple OR3X units (even OR2X). This synch signal must be connected on ext. synch trigger input of each recording unit (see below)

• Active: On/Off Set the synch signal available in sources list, no signal is generated on outputs at this stage
• Generator Mode: Controls synch signal behavior.
• On: start the synch clock generation (0 / +2 V square @ 50 Hz)
• Off: stop the synch clock generation followed by a -2V step during 1 sec.

Track assembly procedure.

1. Activate the synch signal

2. Select Front-end / Output 1 / source = Synchro

3. Set Front-end / ext synch / coupling = DC on each recording unit

4. Set Front-end / ext synch / threshold = 1 V on each recording unit

5. Set Recorder/trigger/start = ext synch on each recording unit

6. Add ext. sync track to the recorder on each unit

7. Set same recording duration on each unit

8. Run each unit

9. Set generator mode = on to start record

10. Download all recorded files on one PC

11. Launch ’Track Assembler’

The concatenation synopsis is shown on the following scheme:

More information on the Track Assembler in ’Operation on multiples Hardware’.

Playing recorded channel on output

Back to the roots of vibration analysis: Everybody knows that our ears and brain is the best instrument to feel and interpret vibration signals. This is also why we take so much care in removing these NVH signals from our machines, vehicles and appliances. The audio playback of vibration (or any other) signal allows the user to "listen in" on what your OROS analyzer is "hearing".

Extending the existing input replication on generators outputs, NVGate V8.30 uses the monitor hot swap capability to allow changing the replicated signal during acquisition/recording.

The NVGate synopsis is as follows:

To activate it, simply connect one of the monitor Channels to the desired output from the Acquisition/Outputs/Signal dialog.

Then you can add any front-end input to the monitor channel. The selected input signal will replicate (play) on the output. You can swap form one input to another at any time including during the run and signal recording

NB: Remember to switch the output impedance to 600 Ω for better listening quality.