SLX Noise Suppressor II User manual

Copyright © 2006 SLX, Inc. All rights reserved.

"A Smart PreAmp"
"I Never Knew my UT
Instrument could
Perform So Well!"
Interfaces to any Flaw Detector, new or old,
analog or digital, in both Pulse-Echo and
Pitch-Catch modes
Flaw Detector Settings for Interface to NSII
•Mode = Dual (even for Pulse-Echo)
•Damping = 50 or 150 ohms
•Gain (w/out NSII) = 30 to 50db min
•Gain (w/ NSII) = Reduce by amount
added up front by NSII
Total Gain = PreAmp (30db) + Filter A (15db) + Filter B (15db) = 60db
N
No os se e S Su up pp pr re es ss so or r I I™
™
i
iI I
Set either Filter = NULL to
suppress an undesired signal
(i.e., noise)
Set both Filters = NULL to
"double up" suppressing an
undesired signal
Set either Filter = MAX to boost a
weak signal
Set both Filters = MAX to "double
up" boosting a weak signal
Tuning selects any Frequency
within model's range
Five ranges: 50 - 240 KHz
150 - 700 KHz
0.5 - 2.4 MHz
1.5 - 7 MHz
8 - 25 MHz
The Filters are sharply peaked &
shaped like a Gaussian distribution
BandWidth controls the Filter's
width and is a % of center
frequency: Low=20%
Mid=30%
Wide=60%
Always use at the highest
setting, without clipping, for
both boosting a weak signal and
suppressing noise
Three Functions – PreAmp + Two Tunable
Filters used to:
• Increase S/N
• Suppress Noise
• Channel Gain into a Narrow Band
to create a "Smart PreAmp"
512 Ashford Road Silver Spring, MD 20910 (p) 301-589-2265 (f) 301-587-3228 [email protected] www.SLX-inc.com
Copyright © 2006 SLX, Inc. All Rights

SLX , Inc.
512 Ashford Road
Silver Spring, MD 20910
Phone: [phone]
Fax: [phone]
E-mail: [email protected]
Web: www.SLX-inc.com
Smart PreAmp / Noise Suppressor II
The NSII is produced in five models. Each model functions identically except for its own
operating frequency range:
NSII-H
8 to 25 MHz (Model NSII-H has one filter, Filter A)
NSII 1.5 to 7 MHz
NSII-L 0.5 to 2.4 MHz
NSII-XL 0.15 to 0.7 MHz (150 to 700 KHz)
NSII-XXL 0.05 to 0.24 MHz ( 50 to 240 KHz)
The
NSII-H ("H" = high) is used for high resolution, high frequency applications including
thin-walled tubes where IRIS-type systems are employed. The
NSII is used for general
NDT inspection work. The
NSII-L ("L" = low) extends down into the KHz range and is used
for lower frequency applications. The
NSII-XL ("XL" = extra low) is for very low
frequency NDT work, such as thick sections, where transducers in the KHz range are
commonly used. The
NSII-XXL ("XXL" = "extra extra low") is for extremely low
frequency applications.
The
NSII can be interfaced to any type of UT instrument, analog or digital, new or old. It
operates in both the single transducer pulse-echo and dual transducer pitch-
catch/through-transmission modes. It is an add-on unit and it is connected between the
transducer(s) and the UT instrument's receiver. It does not affect any of the UT
instrument's operations, including its vertical linearity calibration.
The
NSII is small [7inL x 4inW x 1.5inH (18cm x 10cm x 4cm)], lightweight [14oz (0.4kg)],
and ruggedized for field operation. It runs on either 9v dc power or ac power.
When used as a Smart PreAmp,the
NSII provides selective amplification , which means it
boosts the desired signal only . The Smart PreAmp feature can also suppress noise . Gain
is adjustable in steps of 10, 20, 30, 45, and 60 dB.
Adding the
NSII to your NDT toolbox is an inexpensive way of obtaining a very significant
performance enhancement from your UT instrument for either selectively amplifying
signals, boosting weak signals, or suppressing noise and other undesired signals.
It is easy to use and, best of all, it really works!
Copyright © 2006 SLX, Inc. All Rights

Noise Suppressor II – "Here's how it works"
SLX , Inc.
512 Ashford Road
Silver Spring, MD 20910
Phone: [phone]
Fax: [phone]
E-mail: [email protected]
Web: www.SLX-inc.com
The main point that is stressed continually in the documentation is to use as much PreAmp gain as
possible (up to 30 dB in 10 dB steps) for BOTH the "Max" (i.e., enhancing weak signals) and "Null" (i.e.,
suppressing noise signals) as long as you don't observe clipping (same as signal "flat topping") on your UT
instrument's display. This will give you the very best signal/noise response.
The BandWidth (BW) switch (for each Filter) has 3 positions -- Low, Mid, Wide. You will normally find
that Low, or sometimes Mid, to be best for "Gain"ing weak signals and Wide to be best for "Null"ing
noise signals. Play around and see for yourself.
Keep in mind that "noise" is defined as any undesired signal. It can truly be a noise spike or grain back-
scatter, but it can also be any legitimate signal -- such as a geometrical reflector -- that is undesired.
There are two ways to improve the S/N ratio -- either by boosting a weak signal via the Max setting or
by suppressing an undesirable signal via the Null setting. Here's how each approach works:
(1) Set one of the Filters for "Max" (and leave the other Filter Off for the time being) and dial the
FREQuency switch until you observe the weak signal of interest to increase in amplitude. Dither the
FREQ switch until you achieve the max response (remember that the PreAmp will have been set as high
as possible and the Filter's "Max" setting provides an additional 15 dB of Gain just in that band). Try
both the Low and Mid BW settings to find the optimum response. Then turn on the other Filter ("Max"
setting) and set its three switches to the identical settings thereby adding another 15 dB in just that
band (and nowhere else). You now have created 60 dB of gain (PreAmp = 30dB; Filter A = 15dB; Filter B =
15dB) in
one specific frequency band prior to your UT unit seeing the signal. Cut down the gain in your UT
instrument until the desired signal comes down out of saturation and you should see a dramatic
improvement in the S/N ratio.
(2) Set one of the Filters for "Null" (and leave the other Filter Off for the time being) and dial the
FREQuency switch until you observe the "grass" surrounding the desired weak signal decrease in
amplitude. Dither the FREQ switch until you achieve the greatest decrease (again using the PreAmp). You
should find the BW setting of Wide gives the best result. You have now created a notch filter with a 20
dB attenuation in just that specific frequency band. Now turn on the other Filter ("Null" setting) and set
its three switches to the identical settings, thereby producing another 20 dB drop in just that band (and
nowhere else). You now have created a 30 dB signal amplitude increase (via the PreAmp) and a 40 dB
attenuation in just
one specific band . Therefore, your desired signal (and everything in the sweep
including the grass) enjoys a 30 dB enhancement while the undesired signal in the band suffers a 40dB
attenuation. The net gain is now 30 dB for everything outside the specific notch band and a -10 dB "gain"
(30 dB gain - 40 dB attenuation) for everything inside the specific band. Again, you should see a dramatic
improvement in the S/N ratio.
One final tip involves the use of both Filters in the "doubling up" mode (as described above) when
suppressing noise in the "Null" mode. Try setting the FREQ switch for the 2nd filter about twice as high
as the optimum setting found in the first filter. Sometimes you can pick up a harmonic of the noise signal
and cause even more of a reduction.
Copyright © 2006 SLX, Inc. All Rights

SLX , Inc.
512 Ashford Road
Silver Spring, MD 20910
Phone: [phone]
Fax: [phone]
E-mail: [email protected]
Web: www.slx-inc.com
Interfacing
The
Noise Suppressor II to a UT Instrument
NSII Settings
•PreAmp set as high as possible without clipping signal for both signal
enhancement and noise suppression
UT Instrument Settings
•Dual mode setting – even for pulse-echo inspection
•Input Impedance – set either at 50 ohms, 100 ohms, or 150 ohms, whichever
produces the best signal
•Gain – set to at least 30dB to 50dB while NSII is in Bypass mode so that it can
be reduced after the NSII is functioning
•Filter –do not use any filtering in the UT instrument; set UT instrument to
either "wideband" or "no filter"
Troubleshooting Tips
•Clipped Signal is usually due to a large amplitude input signal that is
saturating the NSII's amplifiers; try reducing the PreAmp level and/or placing
a 10dB or 20dB in-line barrel attenuator connected to the IN port of the NSII
•High Baseline Noise is usually caused by setting the PreAmp too low;
increase the PreAmp to maximum and reduce the UT Instrument gain
Copyright © 2006 SLX, Inc. All Rights

Noise Suppressor II – Summary User's Guide
SLX , Inc.
512 Ashford Road
Silver Spring, MD 20910
Phone: [phone]
Fax: [phone]
E-mail: [email protected]
Web: www.slx-inc.com
Interfacing
NSII to UT Instrument
1. Put Flaw Detector (FD) into dual-transducer mode
2. Refer to back cover of NSII for hookup for pulse-echo or pitch-catch/thru-transmission
3. Remember to take out the gain in the FD that's been added by the front-end NSII
Suppress Noise
1. Set the PreAmp to at least +10 dB - higher is usually better, as long as saturation does not occur
2. Reduce the FD's gain by approximately the amount added in the PreAmp
3. Start with Filter A only and turn Off Filter B (Model NSII-H has one filter, Filter A)
4. Set up Filter A as: GAIN=Null BW=Wide
5. Tune FREQ knob until noise signal amplitude decreases; then fine tune to get minimum amp
6. "Double Up" to get further noise reduction by setting Filter B to same settings (not for NSII-H)
7. Try tuning Filter B to a different FREQ to see if additional harmonics of the noise signal can be
suppressed
Enhance Signal
1. Set the PreAmp to at least +10dB - higher is better, as long as saturation does not occur
2. Reduce the FD's gain by approximately the amount added in the PreAmp
3. Start with Filter A only and turn Off Filter B (Model NSII-H has one filter, Filter A)
4. Set up Filter A as: GAIN=Max BW=Low
5. Tune FREQ knob until weak, desired signal amp increases, then fine tune to get max amp
6. Reduce the FD's gain by the amount added by Filter A (approximately +15 dB)
7. "Double Up" to get further signal enhancement by setting Filter B to same settings (not for NSII-H)
8. Reduce the FD's gain by the amount added by Filter B (approximately +15 dB)
9. Try turning BW knob to Mid or Wide settings to see if s/n improves; if not, return to Low setting
Note on Saturation/Clipping
The NSII will saturate if the INput signal exceeds 3V. If you see saturation/clipping on the FD's display
(such as the signal level not increasing with PreAmp gain), reduce the INput signal by either decreasing the
pulser voltage and/or adding an attenuator at the NSII's INput bnc connector.
Copyright © 2006 SLX, Inc. All Rights