• What does MTI Instruments manufacture? See answer

  MTI Instruments designs, manufactures and markets precision noncontact gaging sensors based on laser, fiber-optic and capacitance technologies for displacement, vibration, position and thickness measurement applications.

• What standard outputs are included in the MTI products? See answer

  All MTI Instruments products provide a -5 to +5, or 0-10 V dc analog output. The Microtrak 7000 laser also includes, as standard, an RS-232 output.

• Which of the MTI products has the highest frequency response? See answer

  The MTI-2000 with MTI-2125R, or H style probes can operate with a frequency response as high as 500 kHz. Our capacitance and laser products can go as high as 20 kHz.

• What is MTI's typical product warranty period? See answer

  One (1) year parts and labor. A copy of MTI's warranty is available upon request.

• Does MTI Instruments have OEM non-contact measurement sensors? See answer

  Yes we do offer OEM versions of all of our products for specific customers. Minimum quantities are required.

• Does MTI Instruments offer demonstration equipment or do sample testing? See answer

  Yes, MTI has a full line of Demo equipment for potential customers to determine how the equipment will work in their specific application.

  MTI will also perform in-house sample testing to verify if our measurement tools are a viable solution.

• What is Noise? See answer
  1. An unwanted random variation of the output voltage in an electronic system,
  2. Electromagnetic radiation that is composed of several frequencies and that involves random changes in frequency or amplitude.
• What is "standoff"? See answer

  Standoff is the nominal distance from the sensor to the target and is typically at the center of the measurement range.

• What is the longest cable length available on MTI products? See answer

  Microtrak II Laser	100 feet
  Microtrak 7000 Laser	27 feet
  MTI-2000 Fotonic Sensor	20 feet (Depending on size of probe 40-50 feet is possible)
  Accumeasure Capacitance Sensors	30 feet

  Longer cables have been successfully used in special applications.

• What are the advantages of the Accumeasure Capacitive Sensor vs Eddy Current? See answer

  Eddy Current	Capacitive Sensor
  Calibration is influenced by target material properties	Calibration NOT influenced by target material properties
  Typically output is noisier than capacitive sensor	Lower noise than eddy current
  Susceptible to drift	Very stable and repeatable output
  Calibration influenced by temperature of target material	Calibration NOT influenced by temperature of target material
  Calibration influenced by magnetic fields near sensor	Calibration NOT influenced by magnetic fields near sensor

• Minimal Phase Delay with Accumeasure 5000 amplifiers. See answer

  The Accumeasure 5000 Capacitance Displacement Amplifier has a high carrier frequency of 100kHz and is ideally suited for displacement measurements from DC to greater than 20kHz. For most applications its phase delay is adequate, but when it is necessary to get very low delay in the displacement signal (e.g.: a servo control), an optional Bessel filter can be ordered. Ordinarily the Accumeasure 5000 amplifier is provided with a five-pole Butterworth filter that has a well defined -3dB cutoff frequency and phase shift.

  Fig 1: Bessel Filter Response
  

  The Bessel filter has a less distinct cutoff and linear phase shift that is very small at frequencies well below the cutoff frequency. The 5 pole 20kHz Bessel filter modification contributes little over 100 microsecond (1x10-6 second) time delay to the input signal when tested with a step-input signal.

  Figure 1 (above) shows the Bessel filter response to a step input change. The gray trace is the displacement input the red response is the amplifier output.

  Figure 2 (below) shows the original five-pole Butterworth response. Note the signal instability at the top of the waveform where the target would be closest to the probe.

  Fig 2: Five-Pole Butterworth Response
  

  Although the ringing noted in the response is seemingly small it would be detrimental to a high accuracy closed loop servo system.

  For more information on the custom Bessel filter option contact MTI Instruments' application engineering at 518-218-2550.

• I want to use the Accumeasure capacitance products to measure a conductive or semiconductor target. However, I cannot guarantee a DC ground return. How can I accomplish this? See answer

  An AC ground return is sufficient. Another alternative would be MTI's push-pull probe. This sensor has a dual element design with one of the sensors being used as a signal return path. See application note.

• What is the longest cable length available on MTI products? See answer

  Microtrak II Laser	100 feet
  Microtrak 7000 Laser	27 feet
  MTI-2000 Fotonic Sensor	20 feet (Depending on size of probe 40-50 feet is possible)
  Accumeasure Capacitance Sensors	30 feet

  Longer cables have been successfully used in special applications.

• My Accumeasure amplifier reads 13 V dc output, even when I move the probe gap to minimum standoff. What may be wrong? See answer

  Most likely there is an open circuit between the probe and the BNC connector on the amp. Make sure that the probe cable is properly connected and not damaged. Ensure that a ground return wire is connected from the target to the ground input of the amplifier.

• What is the frequency response for the Accumeasure capacitance amplifiers? See answer

  The Accumeasure 9000 and 1500 provide a 5 kHz maximum response, while the Accumeasure 5000 provides a response up to 20 kHz.

• With reference to the Accumeasure amplifiers, what does "Range Extension" or "Push" refer to? See answer

  Each probe type has a standard measurement range as determined by the probe's center or measuring electrode dimensions. MTI amplifiers can be set up with an electronic multiplier to electronically increase this range. For example: a 0.010" range probe can be used with an amplifier with X3 "push". This makes the final system range 0.030", or 3 times the basis probe range.

  There are certain limits to how far this range extender can be increased. Consult MTI for more details.

• How do I determine the sensitivity of a capacitance probe? See answer

  The range of the probe divided by the full-scale voltage output determines the sensitivity of a capacitance probe. The full-scale output is 10 volts on all of our AS-9000, AS-5000, and AS-1500 capacitance systems.

  Ex. ASP-10-CTA Probe

  The range is 0.010 in (0.254mm (254 microns))
  Full Scale Output (FSO) is 10.000 volts or 10,000 mV.

  Sensitivity	= Range/ FSO	=Range/FSO
  	=0.010in/10V	=254/10000 mV
  	=0.001 in/V or 1uin/mV	=0.0254 um/mV

• What is the noise value for the AS-9000, AS-5000, and AS-1500? See answer

  The Capacitance amplifiers noise specification is determined by what frequency response filter is being used in the amplifier.

  The AS-9000 and AS-5000 will have the same noise value at the same frequencies.

  AS-9000 and AS-5000

  Frequency Response filter	Noise in mV p-p
  10Hz	0.15
  500Hz	1.0
  1kHz	1.4
  5kHz	3.2
  10kHz*	4.5
  20kHz*	6.3

  The AS-1500 noise will be approximately 5 times greater than the AS-9000 and AS-5000.

  * Only the AS-5000 can have these frequency response filters greater than 5kHz.

• How do I determine the resolution of an AS-9000, AS-5000 or AS-1500 capacitance sensor? See answer

  To determine the resolution of a capacitance system you will need to know the noise of amplifier and the sensitivity of the probe that you would like use.

  Resolution = Noise X Sensitivity.

  Example:
  AS-5000 with a 500Hz frequency response filter ASP-2-ILA probe. Range of probe is 0.002 in (50.8 um)

  AS-9000 and AS-5000

  Sensitivity of the ASP-2-ILA is Range/Full Scale Voltage

  Sens.	= 2 mils/10V
  	= 0.2mils/V
  	= 0.2uin/mV

  Noise of the AS-5000 with a 500Hz filter is 1.0mV.

  Resolution	= Sensitivity*Noise	= Sensitivity*Noise
  	= (0.20 uin/mV)*(1.0mV)	= (0.0051um/mV)*(1.0mV)
  	= 0.20 uin	= 0.005um or 5 nm

• How do I check my MTI-2100 Edge Probe for proper operation in High Resolution Mode? See answer

  If an edge probe becomes damaged or the lamp begins to wear out it is very possible you will read lower Total Indicated Runout (TIR) signal in high resolution mode. Here is what has happened:

  Assume a chipped prism or severely scuffed prism face. The user initiates calibration mode and the MTI-2000 scales the probe up to 10 volts output in Normal (X1 gain). The user then positions the probe at the 50% occlusion over the disk edge and selects High resolution probe sensitivity. Here is where the sensitivity problem occurs. The Probe may only increase X4 or X5 not X7.5 as intended. The reason is that out of a total lamp power of 100% the initial cal cycle used up more than 13% of the total light available so perhaps 20% of the total light available. Now when you select high resolution and the lamp servo commands 7.5 times more powerful light the servo is only able to deliver 100% light not 7.5 x 20% or 150% as was desired by the user and required by the instrument calibration. This means damaged probes will always give a lower TIR sensitivity than expected.

  One way to check for this problem is as follows:

  • Select Normal probe gain on the probe module.
  • While off the edge of the disk select cal cycle (MTI-2100 cals to 10.0 volts)
  • Go to 50% gap, rotate disk.
  • Select p-p mode and read the peak to peak displacement right off the MTI-2000 display. Record it.
  • Select displacement mode,
  • Select high gain on probe module and add appropriate DC offset to center reading.
  • Select p-p mode and read the peak to peak displacement right off the MTI-2100 display. It should be the same TIR reading as normal (X1) gain (less than 10 % to accommodate lamp illumination pattern change) . If not within 10% the prisms have been damaged or fibers have broken and the probe should be repaired.

  Probes sent to MTI Instruments Inc. for calibration are checked to make sure the lamp servo can achieve 7.5 gain increase. It is part of the calibration procedure.

  *The target used here is the edge of a hard disk mounted in a disk drive assembly.

• How do I know that the target I am using with my Fotonic Sensor has sufficient reflectivity? See answer

  The MTI-2100 is calibrated, by a push of the button, against the target you plan to measure. If the target does not provide enough reflectance, the MTI-2100 will indicate a "Cal Error" alarm. As a general rule, a target, which has a surface finish of at least 100 microinches or smaller, would be sufficient.

• How do I determine which MTI-2100 probe module is best suited for my application? See answer

  Larger fiber optic probes offer higher frequency response and thus lower noise. Two factors: A) target size; and B) anticipated range of measurement determine appropriate module selection.

  The target size must be larger than the active area of the fiber optic bundle. For example, if the target size is 0.050", then the smallest useable probe is an MTI-2062R or H, which has an active bundle diameter of 0.047".

  The desired measuring range also will determine which probe to use. Each Fotonic probe has two measurement ranges. Range 1 is the smaller, more sensitive range; while Range 2 offers longer ranges.

  The MTI-2062R is the most common, general-purpose probe module, with excellent response and low noise.

  For High-Resolution applications requiring 0.001" or less range, the MTI-2032RX High-Resolution probe module is a good choice. Consult MTI's Applications Department for further details.

• How can I obtain longer ranges than what is shown on the MTI-2000 brochure? See answer

  MTI can supply "Retro-Reflective" tape, which when used on the target can greatly extend the measuring range to 1" or 2". The longer range results in a decrease in resolution.

• The target which I plan to measure with the MTI-2100 Fotonic Sensor has a voltage potential on it. What can be done when making this type of measurement? See answer

  MTI offers non-metallic tips in cases where there are large voltages present on the target. The rugged non-metallic tip is typically 3" long and offers excellent voltage isolation for the sensor probe and electronics.

• I want to use the more sensitive front slope of the MTI-2100, but would like additional standoff from the target. What can I do? See answer

  MTI offers a model KD-LS-1A optical extender that provides additional standoff of up to 0.375" from the target being measured. The KD-LS-1A easily attaches to the tip of the Fotonic probe and does not affect the system sensitivity.

• I see that MTI offers optional bent tip probes on the Fotonic Sensor. How can I determine the minimum bend radius available and suggested probe tip length? See answer

  Request the bent tip probe worksheet from MTI. MTI can also offer suggestions on the recommended bent tip configuration.

• What is the difference between "specular" and "diffuse" targets? See answer

  The MT100 series 1" standoff heads are specular heads, i.e.; they can only be used when measuring to a specular or mirror-like surface. These heads offer the highest resolution, but the shortest measurement range. In many cases, a target can be made specular by the addition of a small first-surface mirror attached to the surface to be measured.

  Diffuse heads, which have either a 2.5" or 6" standoff, are used on targets which are not shiny and are rougher. Examples of these targets would be dull, painted surfaces, opaque plastics, and many rough machined or grainy metals. A specular surface can be made into a diffuse surface by attaching a small "Kodak" white paper target to the area to be measured. MTI can make recommendation with regards to surface finishes.

• What is the longest cable length available on MTI products? See answer

  Microtrak II Laser	100 feet
  Microtrak 7000 Laser	27 feet
  MTI-2000 Fotonic Sensor	20 feet (Depending on size of probe 40-50 feet is possible)
  Accumeasure Capacitance Sensors	30 feet

  Longer cables have been successfully used in special applications.

• How should the Microtrak laser heads be orientated? See answer

  When you plan to measure a step or groove, position the laser sensor head so the receive optics view the groove. Position the long axis of the laser head so it is parallel to the groove.

  

  When measuring rotating targets the long axis of the laser head should be mounted parallel to the rotating axis as shown below.

  

• What is the difference between a Class II and a Class IIIA Laser? See answer

  The difference between the two classes of laser relates to the output power. The class II laser output is <1mW. The class IIIA laser output is between 1 and 5 mW.

• What is the Microtrak II RS-485 comm port resolution (bit size of a single sample)? See answer

  A sample size is 16 bits, but it requires 5 overhead bytes for data sequencing/formatting . Assuming the controller is set up for the most fast transmission scheme which is "timed telemetry transmit" then the maximum read rate is 2057 samples second. We are assuming the host computer can handle this speed with no delays.

• What is the Microtrak II maximum sample rate from a single node (samples/time)? See answer

  2057 RS-485 samples second. This is baud rate limited to 115kbs. The controller is sampling the laser spot 40,000 times a second and the analog output bandwidth is 20kHz.

• Does every Microtrak II node sample contain a header? How long it is? Can it be disabled? See answer

  The digital output telemetry package is 7 bytes. It cannot easily be made shorter. However, we would consider reducing the data stream length if many units were to be purchased.

• What is the minimum delay through a Microtrak 7000? See answer

  We calculated the time delay of a 18kHz sine wave through a Microtrak 7000 to be 1 complete sample cycle plus one additional half cycle due to digital processing plus the analog output filter delay. One sample cycle is 55.5 µs. This adds up to 82 µs (digital) + 12 µs (analog) for a total delay of 94 µs. Jitter between different Microtraks is -0 µs +27 µs due to startup variation.

• What is the phase delay of a Microtrak 7000 at low frequencies? See answer

  With no smoothing enabled it is -2 degree at 50Hz with a linear drop off of 6 degree per 200Hz. So the phase at 250Hz is -8 degree.

• What is the longest cable length available on MTI products? See answer

  Microtrak II Laser	100 feet
  Microtrak 7000 Laser	27 feet
  MTI-2000 Fotonic Sensor	20 feet (Depending on size of probe 40-50 feet is possible)
  Accumeasure Capacitance Sensors	30 feet

  Longer cables have been successfully used in special applications.

There are currently no questions in this category.

• What is the PBS-4100 system, and what does it do? See answer

  The PBS-4100 system is an engine vibration diagnostics tool, which can be used to:

  • Quickly measure engine vibration levels
  • Quickly identify sources of vibration
  • Accurately guide repair decisions
  • Quickly calculate trim balancing solutions
  • Store engine vibration data

  The PBS-4100 portable trim balancing system is designed to save engine maintenance teams time and money. The PBS-4100 will quickly measure engine vibration levels to determine if the readings are within desired limits. Next, the PBS-4100 system will identify if the vibrations are caused by the engine's fan or turbine, or from other sources. When the source of vibration is identified to be the fan or the low-rotor, the PBS-4100 system determines the optimum set of trim balancing weights required to reduce the vibrations (trim balancing). The PBS-4100 equipment also stores engine vibration data to permit printing, data reviews and continuous tracking of engine performance.

  By quickly solving vibration problems, the PBS-4100 saves maintenance crews valuable time, and also helps operators control costs by minimizing fuel consumption and repair activities.

• The PBS-4100 sounds complicated. Is it hard to operate? See answer

  The PBS-4100 is actually very easy to operate. The PBS-4100 system is able to do so many things because it actually combines four different tools into one system:

  • Vibration survey analyzer/tracking filter
  • Frequency spectrum analyzer
  • Digital oscilloscope/voltmeter
  • Balance analyzer

  The vibration survey feature displays engine vibration across any selected speed range. Both broadband and Nl synchronous vibrations are displayed, providing users with valuable information regarding how much of the total vibration is due to engine unbalance, and indicates the speeds at which the highest vibrations occur.

  The frequency spectrum feature provides a high-resolution, real-time 400 or 800 line spectrum of engine vibration amplitude versus frequency. Users can use the spectrum to quickly determine how much vibration each engine rotor and each engine accessory is causing. This information helps diagnose a wide assortment of engine problems. Many times this information saves users significant amounts of time and money by helping to avoid unnecessary engine removals by.

  The oscilloscope feature provides a real-time display of electrical signals, which can be used to check sensor signals and detect faulty sensors, bad wiring, and solve other test equipment problems. This helps avoid wasting time working with bad data or trying to solve instrumentation problems via trial and error.

  The vibration survey and frequency spectrum both provide information needed to make a quick assessment of an engine's health. If trim balancing is required, the PBS-4100 provides the user with the most sophisticated balancing techniques available.

  The PBS-4100 Balancing Wizard calculates a balancing solution for engines that have excessive vibration due to imbalance. The Balancing Wizard guides users through the process of balancing and gives users a graphical solution that is easy to understand and implement. The PBS-4100 Balancing Wizard will solve complex balancing problems using one or two vibration sensors, and from one to 20 individual operating speeds. The Balancing Wizard even provides a prediction of the resulting engine vibration levels even before the weights are installed!

• What makes-up a PBS-4100 system? See answer

  The two primary components of the PBS-4100 system are a "laptop" computer and a Data Acquisition Unit (DAU). The laptop computer is a ruggedized state-of-the-art "IBM-PC compatible" equipped with a fast Pentium class processor, large color display, plenty of memory, and a high speed CAT5 Ethernet interface for high speed communications.

  The DAU contains the data acquisition circuits that receive tachometer and vibration signals from the engine and convert these signals into a digital form suitable for computer analysis. The DAU transmits these digital signals to the laptop computer via a reliable high speed Ethernet interface. The DAU is housed in a rugged aluminum case and both the laptop computer and DAU can be powered from a wide variety of AC sources (115/230 VAC, 50/60/400 Hz).

  In addition to these two key system components, cables and accessories are required to connect the system to the engine under test.

• Where can I use a PBS-4100 system? See answer

  You can use a PBS-4100 system anywhere you are operating an aircraft engine.

  The portable version of the system is specifically designed to be used on-wing. It is easy to carry, can operate using aircraft power, fits easily into all aircraft, can be used on all types of engines, and has accessory cabling systems for all aircraft types.

  Although the portable version of the PBS-4100 can also be used in engine test cells, we offer a version specifically designed for test cell applications (PBS-4100R). The PBS-4100R is designed to be mounted in a rack of test equipment, and also has some extra features to meet the special testing needs of test cell operators.

• Is the PBS-4100 easy to use? See answer

  The PBS-4100 is very easy to use. The PBS-4100 computer give the user a "Windows" style set of displays and buttons that are easy to control using either the built-in touch pad or the full-color touch-screen display. For balancing activities, the PBS Balancing Wizard guides the user every step of the way to ensure success.

• What engines can be tested using the PBS-4100? See answer

  The PBS-4100 works on any engine model from any manufacturer. Engine parameter diskettes are available for almost any engine type and each one consists of nearly 200 engine-specific parameters. If you are operating an engine model that we don't have parameters for … we will gladly prepare one for you.

• I have an older PBS-4100 system, can I upgrade it? See answer

  Yes. Many of our customers have been upgrading their old systems to the current production configuration. Upgrading is relatively inexpensive, yet results in a much faster system, new features, and a new state-of the art computer.

• How long does it take to set up the PBS-4100 system? See answer

  Setup of the PBS-4100 is very easy. The system only requires an engine speed signal and one or two vibration signals. On newer aircraft, these signal are all available at the AVM maintenance connector and connection time is typically less than 15 minutes. On aircraft without AVMs, users connect directly to the engine to get these signals. Because this involves opening the engine cowls and running cables up to the cockpit area, connection time will average about 30 minutes.

• Can it be used on-wing? See answer

  Yes. The PBS-4100 system was designed for use on-wing either on the flight line or at remote maintenance stations. It is portable, and it operates from aircraft power (115VAC/400 Hz) or normal 115/230 VAC, 50/60 Hz power, and is autosensing, autoswitching. The PBS-4100 can also be used in-flight to acquire data during normal engine operating conditions.

• How do I hook up to the aircraft wiring? See answer

  The PBS-4100 system utilizes several ways of connecting to the aircraft wiring to obtain the necessary speed and vibration signals. On many aircraft, the signals you need are all available at the AVM or Signal Conditioning Unit output. To access these signals, you need to use an interface cable to run these signals to the PBS-4100 and aircraft instrumentation simultaneously. If you do not want to use the normal aircraft instrumentation during tests, you may connect the PBS-4100 directly to the engine using an alternate set of cables and accessories. No matter which method you utilize, we suggest locating the PBS-4100 near the aircraft cockpit to ease communication with the engine operator. The signal connections would then be run from the PBS-4100 to the avionics bay for hook-up to the aircraft's systems, or back to the engine.

• How long does it take to balance an engine? See answer

  The time required to balance an engine generally depends on the time required to install the weights on the engine. If it takes 20 minutes for an operator to install the weights, the average engine can be balanced in less than one hour. From setup to pack-up, it has been done in as little as 40 minutes.

• What is given as a balancing solution? See answer

  When the PBS-4100 calculates a balancing solution, it is provided in two different formats - numerical and graphical. The graphical solution is provided with large easy to follow representations of the balance weight flange where holes requiring weights are distinctively noted. Next to the diagram is a table listing the specific weights required and the assigned positions.

  The numerical balancing solution is also provided on the same graphical illustration and includes the actual amount of weight calculated along with the specific angular position of the weight.

• I don't have a 1/rev phase reference signal available from my engine. Can I still use the PBS-4100? See answer

  Yes you certainly can use the PBS-4100 on your engine. Without a 1/revolution speed signal you can still perform vibration surveys and frequency spectrum analysis to diagnose your problems. A phase reference signal is only required for balancing.

  Many engine designs actually have what is called an embedded 1/revolution signal source as part of their N1 speed monitoring systems. This is accomplished by having one special tooth included on the Nl speed sensor wheel, which can provide the required phase reference. Internal circuitry in the PBS-4100 detects this different tooth and generates a phase reference signal at that location. For other engines, a 1/rev phase reference can easily be generated by use of several different techniques.

• What kinds of balance weights do I need? See answer

  The PBS-4100 will always specify a solution using the engine manufacturer's standard balance weight classes. The PBS-4100 can also specify a single weight solution for engines that allow a single "custom" ground weight size. All solutions are provided with the smallest number and smallest size of standard weight classes possible. Additionally, the PBS-4100 will never give you a solution that exceeds the manufacturer's maximum weight limit for the particular engine design.

• What happens if I plan to do a five-speed engine balance, but can only reach three of the speeds before the engine exceeds its vibration limits? See answer

  The PBS-4100 allows you to obtain an intermediate balance solution based only on the three speeds you were able to reach. You can complete the final two speeds after installing the intermediate balance solution.

• My problem is often low-turbine vibration, not fan vibration. Can the PBS-4100 help with this problem? See answer

  Yes. The PBS-4100 can correct for both low-turbine unbalance and fan unbalance. If you are using the single plane solution, the PBS-4100 will calculate the effect on the turbine vibration from weights that are placed in the fan. It will then provide a single set of weights that is the best compromise to lower the turbine and fan vibration simultaneously. If you are doing a two-plane solution, the PBS-4100 will calculate the optimum set of weights to be placed in the fan plane and the turbine plane, and account for the interaction between the two planes.

• Explain two-plane simultaneous balancing. What is its purpose from a cost/benefit viewpoint? See answer

  Generally one-plane balancing (usually the fan) will reduce the vibrations in most engines to acceptable levels. However, placing a weight in the fan of newer high performance engines will frequently upset the vibration levels in the turbine. When this happens, two-plane balancing is required.

  Two-plane balancing is the process of calculating a set of weights that can be installed in both the fan and turbine areas of the engine (two planes) to reduce vibration levels. It is an extremely complicated mathematical process that without the assistance of the PBS-4100 would require more than 8 hours of engine running and calculation time. Chances of successfully balancing the engines without the PBS-4100 are much less than 50%.

  Fortunately, with the PBS-4100 Balancing Wizard, the arduous task of calculating a two-plane balancing solution takes only a few seconds, and the complete task can be completed in less than 1 hour.

• Can we do two-plane trim balancing on complete engine assemblies? I thought that the turbine ends were totally inaccessible. See answer

  There generally is no access to add balance weights on the turbine end of older engine designs. However, some newer engine designs are more lightweight and compliant and require two-plane balancing techniques to achieve acceptable vibration levels. Some engine designs do provide access to the turbine and the fan balance planes, and manufacturers are developing procedures to allow two-plane trim balancing in the field. Two examples are the PW2037 and the CFM56 series of engines.

• Can the PBS-4100 be used for shop balancing of engine modules? See answer

  Yes. The PBS-4100 can be used to trim balance completed engine assemblies or to balance individual engine modules in a shop balance machine. When used for shop balance, you retain all the PBS advantages of accurate solutions, easy operation and use of standard weight classes.

• Will the PBS-4100 balance every engine on the very first attempt? See answer

  No instrument can guarantee that it will balance every engine every time. There will always be the odd engine that responds differently than others of its family, and which will require a customized balance attempt or must be rebuilt due to internal mechanical problems. Our experience shows the PBS-4100 can balance 75% of balanceable engines on the first attempt, and the remaining 25% on the second attempt. For unbalanceable engines, the PBS-4100's diagnostic capabilities allow you to avoid wasting time attempting to balance, and help you determine what internal engine problems exist.

• How do I know when to stop balancing? See answer

  The PBS-4100 provides the current vibration levels as the engine is running. When the engine vibration is within manufacturer's limits, most people will stop balancing at that point. You may continue to refine a balance to obtain lower vibration levels, however, after several attempts the PBS will begin to generate the same solution. This indicates that the vibration level cannot be reduced any further.

• How long has the PBS-4100 been in service? See answer

  The PBS-4100 has been sold commercially since 1986.

• Does the PBS-4100 reduce the cost of balancing engines? How long is the 'payback' period? See answer

  The PBS-4100 saves money by reducing the amount of engine running required to do a balance. The total savings depends on how many engines you normally balance, and on the cost of time and fuel to your operation. Our studies show that most purchasers can pay back the system price in six months to a year. More dramatic savings have been achieved in situations where the superior diagnostic capabilities of the PBS-4100 have allowed a troublesome engine to be balanced on-wing, instead of having to be removed and sent to the shop. In such cases, the PBS-4100 has been paid for instantly!

• Who is using the PBS-4100? See answer

  The PBS-4100 is currently in daily use worldwide for line maintenance, test cell use and production engine testing. Although we cannot provide a complete customer list, our customers fall into categories, which cut across the entire airline industry:

  • US Carriers such as Delta, United, Northwest, US Airways, Frontier
  • Freight Carriers such as Federal Express, UPS and Airborne
  • Non-US Carriers such as Air Canada, Malaysia Air Lines, Cathay, Saudia, Air New Zealand
  • Airmotives such as, AeroOutfitters, AeroThrust , Caledonian, and GAMCO, and TIMCO
  • Engine Manufacturers such as GE, Pratt & Whitney, Rolls Royce and CFMI
• Who is MTI Instruments, and what experience do you have with aircraft engines? See answer

  MTI is a 40-year-old company specializing in the design and manufacture a broad line of products for the test/measurement equipment market and for aerospace. Our engineering and manufacturing facilities are located in Albany, New York (approximately 150 miles (240 km) north of New York City).

  Our experience with aircraft gas-turbine engines is long and varied. MTI developed the original rotordynamics and balancing codes for NASA and for the U.S. Air Force in the 1960's and 1970. Under one contract in the early 1980s, we developed, supplied and installed a system for the U.S. Air Force to perform balancing and diagnostics on re-manufactured engines of any type in the Air Force inventory. This system was installed in 22 test cells, and was recently replaced by brand-new state-of-the-art PBS-4100R systems in 1999. The PBS-4100 brings this same level of expertise and experience to a system designed and priced for the commercial airline industry.

• What do the engine manufacturers say about this system? See answer

  Pratt & Whitney, GE, CFMI, and Rolls Royce have all have purchased several PBS-4100s for their field service and customer support organizations, and also have either PBS-4100s or PBS-4100Rs in their manufacturing and development test cells as well. Most of these manufacturers have or are in the process of adding the PBS-4100 to their engine maintenance manuals as recommended test equipment.

• Should we consider purchasing more than one PBS-4100 balancing systems? See answer

  If you are responsible for a large fleet, and/or have several maintenance sites … multiple PBS-4100 systems will improve your reaction time and will save you time and lost revenue by being available immediately. Without multiple systems you will:

  • Wait at least one day for the PBS-4100 system to be delivered on-site
  • Loose the revenue service of the aircraft
  • Create a scheduling problem for the remainder of the fleet

• Does the PBS-4100 require a lot of maintenance? See answer

  No, the PBS-4100 has been built to survive the flightline and the rigors of aircraft maintenance work. The PBS-4100 is designed to require a minimum of preventive maintenance and service. Most hardware problems can be handled by a simple modular circuit board replacement. We maintain a full complement of spare circuit board assemblies for customer support.

  We do recommend that an annual calibration be performed at the factory, where your entire system is checked and receives a complete factory alignment and calibration inspection.

• How rugged is the PBS-4100 system? See answer

  The PBS-4100 survives the punishment of daily use on the flight line as well as shipment around the world! All internal circuit assemblies are fully supported and shock mounted where necessary. The system has been designed and tested for reliable operation in temperatures to 50C, and has provided reliable service in the hot dry climate of the desert, in high-humidity areas, and in the frozen areas of the north.

• Where can we get our systems serviced? See answer

  You should send your PBS-4100 system back to MTI for factory authorized service. There is a complete supply of service parts, and trained technicians capable of quickly repairing your system.

• Are software updates/upgrades included as part of the system? If so, for how long? See answer

  We are proud of that fact that a liberal no-cost software upgrade and update practice is part of the high-quality service we offer our PBS-4100 customers. Unless the software upgrade makes major software architecture changes, we provide our customers with no-cost upgrades. Most of these upgrades can be easily performed by our customers. Additionally, when systems are returned to our factory for calibration and service, part of the calibration procedure is to ensure that the latest software upgrades are installed.

• Is training available? See answer

  Yes. We can provide training at your facility, or at our factory. Classes are custom tailored to your specific needs and generally consist of two full days of activities. The classes include some theory, but focus more on hands-on time with the system.

• How do I know if my engine needs to be balanced? See answer

  You can easily and quickly determine if the engine needs to be balanced by using the vibration survey and frequency spectrum features of the PBS-4100 system. The vibration survey plots the amplitude of the broadband and N1 synchronous vibration as a function of engine speed. If the PBS-4100 indicates that a significant amount of the total vibration is comprised of N1 synchronous vibration, then you have a strong balancing candidate. If the amount of Nl synchronous vibration is low, and it is not a significant portion of the total vibration, the engine probably doesn't need to be balanced.

  The frequency spectrum is also an excellent tool for diagnosing the cause of vibration because it breaks the engine's vibration signal down into its component frequencies. If the vibration level at the Nl frequency is low with respect to that at N2 or at other engine component frequencies, the engine doesn't need to be balanced.

• Can I use the PBS-4100 system to diagnose other engine problems? See answer

  Yes. In the vibration survey, if the broadband or total vibration reading is significantly higher than the Nl synchronous vibration level, you know there are other factors in the engine causing the high vibration level. You can use the frequency spectrum to identify which components in the engine are causing the high levels.

• Is the PBS-4100 used only when engines need balancing? See answer

  No. The PBS-4100 is a tool that can be used to solve many vibration related problems:

  Because all engines vibrate - the PBS-4100 can tell you exactly how much, and what is causing the vibrations. For example the PBS-4100 will discriminate between vibrations coming from the fan and the turbine. It can also tell you if a fuel pump is causing a significant amount of the vibration. This information in invaluable, and can help you avoid unnecessary engine removals and test cell visits.

  When used on-wing, the PBS-4100 quickly indicates if trim balancing the engine(s) will resolve the problem and enable you to keep the aircraft in service. The quicker you know what needs to be done with the aircraft, the sooner the schedulers can make their final plans! When operating the PBS-4100 on-wing, users can perform all the vibration tests that can be perform in a test cell.

  Trim Balancing can take less than 1 hour on-wing thereby permitting fast turn-around of the aircraft and almost immediate return-to-service.

  In the test cell, the PBS-4100 is used to measure the level of engine vibration on every engine that is tested. If an engine exhibits higher than allowable vibrations, the equipment is also used to identify the source of vibrations, and then the equipment is used to balance the rotor to minimize the vibrations. You can also use the PBS-4100 to record (and store) the final vibration levels of each tested and approved engine.

• What is frequency spectrum analysis? How can it help solve engine vibration problems? See answer

  Engine vibrations are caused by a number of influences including fan imbalance, turbine imbalance, shaft misalignment, loose plumbing and ducting, and failing engine components (gearboxes, generators, fuel pumps, lube pumps, etc.).

  Frequency spectrum analysis is a feature of the PBS-4100 that helps to identify the sources of engine vibrations by isolating the various "components" of the vibration signal. Just as a prism breaks sun light into a rainbow revealing the different colors (or frequencies), the PBS-4100 uses its internal Digital Signal Processor to identify the different frequencies that are contained within an engine's vibration signal.

  Because each of the sources of engine vibration has a characteristic frequency (or set of frequencies) that can used like fingerprints to determine the source of engine vibrations, by using Frequency spectrum analysis, the PBS-4100 can be used to quickly and accurately identify the cause or causes of the engine vibrations.

  Frequency spectrum analysis quickly pinpoints the sources of vibration and minimizes diagnostic costs (labor, parts and fuel). This means that less time can be devoted to diagnosing engine faults, with a much higher confidence level of correct diagnosis.

• What type of sensors does the PBS-4100 use? See answer

  The PBS system can be used with any type of vibration sensor. The PBS system is normally used with the vibration sensors that are installed in the engine by the engine manufacturer. These sensors are the best ones to use, because they are positioned to be most responsive to engine vibration and are used to monitor the health of the engine in-flight.

• Our engines don't have any installed vibration sensors. Can we use the PBS-4100? See answer

  Yes. We offer velocity probes and accelerometers that are specified by the engine manufacturers. We also offer charge amplifiers, cables and other accessories required for testing engines.

• Can the PBS-4100 be used on machinery and equipment other than aircraft engines? See answer

  Yes. The PBS-4100 can be used for vibration diagnostics and balancing on any type of rotating machinery, as long as there are locations available to place balance weights.

• Can I get printouts of the vibration data readings and plots that appear on the PBS-4100 screen? See answer

  Yes. All data displays include a PRINT button, which will automatically begin to print the data displayed on the screen. The small portable, lightweight printer, which is offered as an option to the PBS-4100 system, produces excellent graphs very quickly. You can use the printer to produce copies of vibration surveys, frequency spectrums and balancing solutions. You may also use the printer to print data that you saved during other engine tests.

• Does this mean I don't have to carry the printer to the airplane? See answer

  Yes. Although it's convenient to have a print out of vibration surveys and calculated weight placements while you are working on the aircraft, the PBS-4100 system stores all the collected data. You can connect the printer when you return to your office and print everything you need for record keeping or other uses.

• Can't I just buy the software and use my own computer? See answer

  The PBS-4100 system is more than just a nice software package. It is an integrated hardware and software instrument. Custom designed electronics work together with the software package to provide the user with total data acquisition, diagnostics, and balancing capability.

• My operators are unfamiliar with using a keyboard. What if they push the wrong key? See answer

  The PBS-4100 system is easy to use even for inexperienced operators, and we have never had a user permanently damaged the PBS-4100 system because of an errant keystroke! Using the system is very easy. The PBS-4100 requires operator responses that all consist of easy to follow one and two button responses. Most activities require only a single key press to start a vibration survey, or to save a spectrum plot. Even balancing requires only the pressing of one button to prompt the system to go to the NEXT step in the process.

  In the event that an incorrect key is pressed, the PBS-4100 generally informs the user that an invalid response was given, and offers the user another change to respond.

  Best of all, each PBS-4100 system has a Practice Mode of operation. In this mode, users can operate all of the different functions, without the need of a live engine! It's a great way to lean how to use the system, and it's also a great way to practice using the system before having to go out on the flightline.