| 
Interfacing to a UT Instrument
PreAmp
Noise Suppression
Signal Enhancement
General
Interfacing to a UT Instrument
Can the NSII be used with both analog and digital UT instruments?
Yes. The NSII is located between the transducer and your UT instrument and the signal is always analog at the transducer end.
Does the NSII operate in pitch-catch/thru-transmission mode as well as pulse-echo?
Yes. The NSII operates in both modes. Just check out the hook-up diagram on the back face.
What is the purpose of the Bypass switch?
It enables you to see the effect of the NSII’s filtering action, basically a “before” and “after” comparison. When the POWER switch is set to Bypass, the Input is routed directly to the Output port without passing through any of the NSII’s circuitry.
Does the NSII filter operate only in a gate or across the entire sweep?
Across the entire sweep. Once you set up either a noise suppression or signal enhancement band, or both, it is applied to the entire sweep. This means that a noise signal, for instance, will be suppressed even if it occurs multiple times across the sweep.
What if the input signal is too strong?
Any input signal exceeding about 3 volts will cause the amplifiers to saturate. This will be evident on your UT display screen as a clipped signal. Any attempt to apply additional gain, such as from the PreAmp or either of the Filters, will continue to show a clipped signal. In this case, decrease the input signal’s amplitude by either decreasing the pulser voltage and/or using an external in-line attenuator to decrease the input signal’s amplitude.
Where do I connect an external attenuator?
The best place is at the NSII’s INput connector. Then connect the bnc “tee” to the attenuator (for pulse-echo) or the pulser cable directly to the attenuator (for pitch-catch/thru-transmission).
Why does my UT instrument sometimes goes into saturation when I turn on the NSII?
The most likely reason is that your UT instrument is set to the pulse-echo mode, labeled “single” or “pulse-echo”, etc. You must always use the dual transducer mode when the NSII is connected to your UT instrument, even if you’re operating in pulse-echo mode. So change the setting to dual transducer mode and everything should function properly.
Why does the signal sometimes disappear on my UT screen when I turn on the NSII?
Actually it’s still there but the combined gain of the NSII and your UT instrument is so high that the signal is completely saturated and “pinned” to the top of your screen. Keep decreasing the instrument’s gain until the signal “falls down” and returns to its normal screen position.
Can the NSII be used to improve the performance of “older” UT instruments?
Yes. The NSII provides a front-end noise suppression and/or signal enhancement capability that can significantly improve the performance of older UT instruments and, in some cases, cause them to operate like newer instruments possessing considerably more features.
What is the operating frequency range of the NSII?
The five NSII models cover the range from 50 KHz to 25 MHz. Model NSII-XXL generates between 50 to 240 KHz,Model NSII-XL operates between 0.15 to 0.7 MHz (150 to 700 KHz), Model NSII-L operates between 0.5 to 2.4 MHz, Model NSII operates between 1.5 to 7 MHz, and Model NSII-H operates between 8 to 25 MHz.
Back to Top
PreAmp
Is the PreAmp adjustable?
Yes. The PreAmp provides a total of +30 dB of gain in +10 dB steps. The PreAmp knob has four settings: Off, +10 dB, +20 dB, +30 dB.
How can I use the NSII as an “Smart” PreAmp?
All PreAmps, including the PreAmp function of the NSII, provide additional gain. However, the NSII also permits the output signal to be “shaped” as well as boosted in amplitude. One or both of the filters can be used to either accentuate one portion of the frequency band (the higher frequencies, for instance) or to de-emphasize one portion of the frequency band. So the NSII can provide signal shaping as well as additional, adjustable gain. The capabilities of the NSII in the Smart PreAmp mode are: (1) selective amplification, (2) boost desired signal only, (3) suppress noise, (4) total gain of 60 dB in a specific tunable band, and (5) adjustable in steps of 10, 20, 30, 45, and 60 dB.
Why do I sometimes I see an increase in baseline noise when I turn on the NSII and the PreAmp is off?
The PreAmp should always be set to at least +10 dB. The PreAmp is not only there to boost weak signals, but also to reduce the noise floor of the overall filter unit. The band-pass filter circuits need gain ahead of them to reduce the overall noise of the circuit. The best settings for low circuit noise use as much PreAmp gain as possible without causing the largest input signals to over-range the amplifier. Turn down the levels on your UT instrument to bring the signal back onto the screen. The PreAmp should never be set to 0 dB unless you have extremely large input signals, at which point the circuit noise will be negligible.
Back to Top
Noise Suppression
What types of noise are suppressed?
“Noise” means any unwanted signal. Usually this takes two forms: (1) random spikes (due to motors, welders, cranes, etc.) and, (2) material back scatter (due to grain structure). The NSII can be used to suppress either or both types of “noise”. However, using the more general definition of noise as “any unwanted signal” broadens the use of the NSII in your inspection process. For instance, a geometrical reflector – such as from weld geometry – or the surface wave of a time-of-flight-diffraction setup can also be considered as “unwanted signals”. The NSII can also be used to suppress these signal types.
What frequency range is covered by each of the two tunable filters?
Each filter has 16 discrete steps within the frequency range appropriate to the particular NSII model being used. There is a rotary knob that has clicked detents at each of the 16 positions. For example, the 16 steps for Model NSII are: 0.25 MHz between 1.5 and 3 MHz; 0.33 MHz between 3 and 4 MHz; and, 0.5 MHz between 4 and 7 MHz.
How can I tell which frequency I’m selecting?
The rotary switch for each of the 16 selectable frequencies has detented stops at each position so that the knob is solidly positioned unless moved (“clicked”) to the next position. Each position is also clearly labeled.
How can I find the optimum frequency band for an unwanted “noise” signal?
Follow these simple steps: (1) select one of the two Filters, say Filter A; (2) set the GAIN switch to the “Null” position (this sets up a-20 dB attenuator); (3) rotate the FREQUENCY switch while looking at your UT instrument’s display until the noise signal drops in amplitude (you are now close to its center frequency); (4) rotate the FREQUENCY knob a few steps on either side of this position until you find the largest drop in amplitude (you have now found the center frequency of the noise); (5) lastly, adjust the width of the band by rotating the BW switch through each of its three positions (Low, Mid, Wide) and select the BW position that gives the largest decrease in the noise signal. You will generally find the Wide BW setting works best for noise suppression. Congratulations, you have now found the optimum frequency band and bandwidth to suppress the noise signal.
How can I “double up” on either noise suppression or signal enhancement?
Great question. This feature really shows off the power of the Noise Suppressor II. Let’s start with doubling up on signal enhancement. Once you’ve found the optimum band, say with Filter A, you have applied a gain of +15 dB in this band. You now turn on the other filter, Filter B, and set the three knobs (FREQUENCY, BW, GAIN) to the same settings as Filter A to provide a second +15 dB of gain. You have now applied a total of +30 dB of gain in this band. You can also use the PreAmp to provide an additional “boost” to this signal. Turning on the PreAmp to, say +20 dB, provides a gain of +20 dB across the entire frequency band so that both the signal(s) in your optimum band as well as signals outside of it are all boosted by the same +20 dB. Keep in mind that you now have a total of +50 dB (in this example) in your optimum band. Now if you take out-20 dB at your receiver, the signal/noise is significantly enhanced. Doubling up for noise suppression is done the same, except both GAIN switches are set to "Null" to provide 40 dB total attenuation in the selected band.
Does it matter in which order I use the two filters?
No. The signal flow is Input  Fixed Filter PreAmp Filter A Filter B Output. The signal flow always passes through each of the three subcircuits (PreAmp, Filter A, Filter B), unless it is turned off, so the order is irrelevant irrespective of whether one or both filters are being used.
Back to Top
Signal Enhancement
How can I find the optimum frequency band for a desired signal?
Follow these simple steps: (1) select one of the two Filters, say Filter A; (2) set the GAIN switch to the "Max" position (this sets up a +15 dB gain); (3) set the BW switch to Low; (4) rotate the FREQUENCY switch while looking at your UT instrument's display until the desired signal increases in amplitude (you are now close to its center frequency); (5) rotate the FREQUENCY knob a few steps on either side of this position until you find the largest increase in amplitude (you have now found the center frequency of the desired signal); (6) lastly, adjust the width of the band by rotating the BW switch through each of its three positions (Low, Mid, Wide) and select the BW position that gives the largest increase in the desired signal. Congratulations, you have now found the optimum frequency band and bandwidth to boost the desired signal.
How can I “double up” on either noise suppression or signal enhancement?
Great question. This feature really shows off the power of the Noise Suppressor II. Let’s start with doubling up on signal enhancement. Once you’ve found the optimum band, say with Filter A, you have applied a gain of +15 dB in this band. You now turn on the other filter, Filter B, and set the three knobs (FREQUENCY, BW, GAIN) to the same settings as Filter A to provide a second +15 dB of gain. You have now applied a total of +30 dB of gain in this band. You can also use the PreAmp to provide an additional “boost” to this signal. Turning on the PreAmp to, say +20 dB, provides a gain of +20 dB across the entire frequency band so that both the signal(s) in your optimum band as well as signals outside of it are all boosted by the same +20 dB. Keep in mind that you now have a total of +50 dB (in this example) in your optimum band. Now if you take out-20 dB at your receiver, the signal/noise is significantly enhanced.
Does it matter in which order I use the two filters?
No. The signal flow is Input Fixed Filter PreAmp Filter A Filter B Output. The signal flow always passes through each of the three subcircuits, unless it is turned off, so the order is irrelevant irrespective of whether one or both filters are being used.
Can the NSII be used to “shape” a transducer’s frequency spectrum?
Yes. Either or both filters can be used to either emphasize or de-emphasize a portion of the transducer’s frequency spectrum.
Back to Top
General
Is the NSII an analog or digital device?
Analog. There is no analog/digital conversion taking place so the NSII operates in real-time with no time lag.
Why is there a front-end fixed filter that limits the input signal to the particular NSII model's operating frequency range?
The circuits for the two manually tunable filters (A and B) are optimized for the frequency range of the particular NSII model being used. Any signal outside of this range is considered noise and is severely attenuated by the front-end fixed bandpass filter.
What happens if the signal is outside of the operating frequency range?
The front-end fixed filter begins to roll off at the extremes of the operating frequency range and then rolls off at a rapid rate outside of these values. You will notice a significant decrease in amplitude of the signal when the NSII is in the On mode and the signal is outside of the range.
Are the filters band-pass types?
Yes. The NSII implements band-pass and band-reject filters as opposed to combinations of low-and high-pass filters to create a band-pass shape.
What is the vertical linearity capability of the NSII?
Vertical linearity applies primarily to the UT instrument that takes in a signal, manipulates it internally via one or more circuits and then displays on its screen. Using the double-signal ASTM protocol (one high, one low), the UT instrument’s vertical linearity threshold is determined by how well the smaller signal amplitude linearly tracks the larger signal amplitude as the gain is increased. Any device external to the UT instrument rarely affects its vertical linearity. As with most amplifiers, the NSII is extremely linear up until the point of saturation of the output. Saturation occurs when signals drive the output above approximately 3V peak-to-peak. As long as the UT instrument is set to a range where 3V peak-to-peak is off screen, you will rarely see vertical linearity problems using the add-on NSII unit.
Why does the Model NSII-H have one turnable filter?
The filter design for the High frequency model is different from the other four models because of special electronic design factors that must be employed when dealing with high gain and high frequency simultaneously. This model provides a total gain of 45db in adjustable steps of 10, 20, 30, and 45db when used in either the Smart Pre Amp on Signal Enhancing modes.
Can the NSII be used with EMAT Systems?
No. The NSII is designed to be used with a UT instrument that supplies a broadband pulse to a standard UT transducer.
How can the NSII be used with a Multiplexer?
Generally, the output of a multi-channel multiplexer is a single channel. This single channel Mux output is connected to the NSII's input connector and the output is connected tot he UT instrument. Each of the transducers connected to the Mux must be the same frequency.
How is the NSII powered?
Either by a 9 volt battery or an ac/dc wall plug transformer. Both the battery and transformer are supplied.
How long does the battery last?
The battery lasts from approximately three to nine hours depending on how many of the three independent functions – PreAmp and the two Filters – are being used simultaneously. If a Filter is not being used, it should be turned off, otherwise it will add to battery drainage. Using all three functions should provide approximately three hours of usage. Using only one or two functions will extend the battery life up to around nine hours.
How do you know when it’s time for a new battery?
The red LED display is very bright with a fresh battery (operating at 9 volts) and becomes dimmer as the battery output voltage decreases. The LED turns off when the battery voltage drops below 7.2 volts. The battery should be replaced as the display becomes very dim and certainly when it no longer lights.
What components are supplied with a purchase?
Components included with an NSII purchase include: Noise Suppressor II, 9 volt battery, ac/dc wall cube transformer, calibration record, and operating instructions.
What Optional Accessories can be purchased?
A custom carrying/shipping case is available as an inexpensive option.
Back to Top
|
