Echometer Ultrasonic Bolt load measurement System By BOLTIGHT

Echometer – Ultrasonic Bolt load measurement System

ByBOLTIGHT

www.coretechindustrial.inAn ISO 9001:2015 Certified company

http://www.coretechindustrial.in/


Echometer –Ultrasonic Bolt load measurement System

By



Where it’s used

Most commonly used as load validation method.

When torqueing a joint the coefficient of friction

cannot be accurately known.

Echometer acts as an independent check on

correct joint tightening.

In service monitoring – commonly with wind

turbines.

When the original bolt load is unknown – the

Echometer can be used “backwards” to

determine the load that was removed from the

bolt.



Benefits

• Compared to other methods of measuring

elongation the Echometer is incredibly

fast.

• Can be used to create a permanent

electronic record for bolts and joints –

especially useful for in service monitoring.

• Only minor access is required – useful for

difficult to access bolts.

• In unit measurement conversion (stress,

strain etc.) gives quick overview of what

is happening in the joint.



• It is impossible to give an absolute accuracy value for ultrasonic elongation

measurement.

• This is due to the method having many variables from joint condition to operator

experience.

• From experience with good condition bolts an accuracy with 5% can easily be

achieved.

• This can be improved even further in lab conditions and operator experience and

care.

Accuracy



How itworks

• The Echometer is Boltight’s ultrasonic

elongation measurement system.

• It transmits an ultrasonic pulse into a bolt and

then times how long it takes for that pulse to

reflect back to the transducer.

• The bolt is then stretched and another time

reading is taken.

• This process is shown by the animation to the

right.



How itworks

• The change in time equates directly to the bolt

elongation after tightening.

• This can be combined with the ultrasonic

velocity and stress factor for the material to

convert this change in time into an elongation

measurement.

• This measurement can be directly converted

further into stress, strain or load using

application specific information.



What are thelimitations• Firstly the material must conduct ultrasound – this is

not usually an issue with

bolting steels, but worth noting for exotic applications.

• Only operates at ambient temperature range (-10°C to

80°C) – Measurements at these limits should also try

to be avoided where possible.

• Must be able to take a loaded and an unloaded reading

– it doesn’t matter if the bolt is loaded to begin with,

however if the bolt cannot be loosened then it will be

impossible to get a reading different from the reference

reading.

• Thick coatings or rust create air gaps between

the measuring surface and transducer which

prevents good energy transmission of the

ultrasonic pulse preventing readings.

• Ideally the bolts should have machined ends with a

surface finish of at least 1.6 microns.



• The following few slides refer to the effects of bolt end condition – many of these

will make reference to the reflected pulse creating noise in the bolt.

• Noise refers to random, unpredictable and undesired signals that mask

desired information content.

• With the Echometer noise affects the interpretation of the return pulse as it

causes lower amplitude signals to be received into the transducer at the

same time as the desired pulse reading.

• As shown previously when waves interact they superimpose each other which

can drastically change the shape of the return wave making it difficult to

interpret.

• Because of this noise generation should try to be avoided where possible.

Noise



Transducers and TemperatureProbes

The size and frequency of the transducer is important.

Transducer sizes are specified based on the crystal

diameter.

Choice of frequency will vary depending on material

and bolt length.

Lower frequencies travel further whereas higher

frequencies give a better resolution.

Temperature changes both the physical length and the

ultrasonic length of a bolt.

These change at different rates to each other.

The variation in rate change is what limits the operating

temperature to ambient.

Temperature probes are recommended when

considering in-service monitoring.



Calibration bars are used to perform a zero point

calibration.

Zero point calibration is important if multiple

Echometers are to be used to measure the same

data.

Also if in-service monitoring will last so long as to

require replacement of any of the equipment.

The zero point calibration ensures that each

Echometer, cable and transducer combination are

measuring from the same start point.

Calibration Bars



Basic Principles -Waveform

• The image to the side shows a fundamental sinewave.

• The terminology however refers to all waveforms; simple or complex.

• The amplitude of the wave can also bedescribed as the volume of the wave or sound.

• The period can also be described as pitch,wavelength or frequency.

• With ultrasonics we are actually creating a longitudinal wave in the material as shown in the animation.

• This will be represented as a transversewave (the above picture) for clarity.

• The high density sections are the positive amplitude and the low density are the negativeamplitude.



Basic Principles -Ultrasound

• Ultrasound is the label given to any sounds with a frequency higher

than the upper audible limit of human hearing.

• Frequency of a wave (can also be described as pitch) is measured in

Hertz (Hz).

• Hz is simply defined as number of cycles per second.

• Upper limit of human hearing is 20 kHz (20’000 Hz).

• Ultrasonic elongation measurement takes place above 2 MHz

(2’000’000 Hz).



• A pulse (and a wave) transfers energy through a material of a

consistent density.

• The animation above depicts a pulse travelling down a dense

medium (a bolt) and transferring into a less dense medium (air).

• Note that when the pulse reaches the boundary between then air

and the bolt the energy is divided into a reflected pulse (which

remains in the bolt) and a transmitted pulse (which transfers into the

air).

• The reflected pulse has a smaller amplitude – due to the transfer of

some of the energy into the air.

Basic Principles – SoundsWave Reflection



• The closer the densities of the materials the more energy is

transferred into the second the material and therefore the less is

reflected back up the bolt.

• Note the speed and frequency of the reflected pulse remain the

same – this is due to no change in the material density.

• The speed of the transmitted pulse increases due to the reduced

density of the air however the frequency will remain the same.

Basic Principles – SoundsWave Reflection



Basic Principles –WaveInteraction

• Wave interaction is important to understanding

the performance of an ultrasonic transducer.

• The sound that emanates from an ultrasonic

transduce does not originate from a single

point but instead many points along the

surface of the piezoelectric crystal.

• This results in a sound field with many waves

interacting / interfering with each other.

• When waves interact they superimpose each

other as is shown in the animation to the side.

• The amplitude of the wave at any point is the

sum of the amplitudes of the individual waves.



• Ultrasonic velocity of a material refers to the speed at which an

ultrasonic pulse will travel through the material in question.

• The ultrasonic velocity of a material is affected by interactions of a

materials microstructures – also known as the grain structure in

steels.

• As the grain structures in steels vary slightly from sample to sample

so too does the ultrasonic velocity.

• Measuring ultrasonic velocity is as simple as measuring the time it

takes for a pulse of ultrasound to travel from a known length of

material and back again.

• This technique is known as pulse echo and is suitable for

estimating acoustic velocity to 1% accuracy.

Basic Principles – UltrasonicVelocity



Ultrasonic Length vs PhysicalLength

• When the initial reference time for a bolt is taken it is usually displayed as a

reference length.

• Note that this length is an ultrasonic length rather than a physical length and

will most likely vary slightly from the physical length of the bolt.

• The materials programmed into the Echometer initially are based on large

sample material testing to generate an average value for each material.

• In reality each sample will have a slightly different ultrasonic velocity.

• This is due to variations in the grain structure from sample to sample

mentioned previously.



• An ideal bolt will transfer as much sonic energy as

possible from the transducer into the bolt. The

energy will be sent directly down the centre of the

bolt and back into the transducer.

• Avoid rough or irregular surface finish. While this

can be filled with couplant it still results in reduced

energy transmission and signal dispersion.

• Avoid non-perpendicular ends. If the bolt end is

not perpendicular to the bolt axis then the energy

will be transmitted toward the side wall. This will

result in the signal reflecting along the bolt and

yield poor signal quality and measurement errors.

Bolt End Condition –Transducer Placement



Bolt End Condition –Transducer Placement

• Avoid bolt ends with raised grade marks or

indentations with a raise edge. These can cause

the transducer to be seated at an angle preventing

adequate contact.

• Avoid bolt ends with numerous or large

indentations. Small indentations can be filled with

couplant, this reduces signal strength slightly but

normal measurement should still be possible.

Many or large indentations cause too much of a

reduction in signal strength to allow accurate

results.



Bolt End Condition –Reflection End

• Avoid rough reflecting bolt ends. Similarly to the

transducer placement if the reflecting end of the

bolt is rough or curved, most of the reflected

energy will be dispersed and a weak or distorted

echo will be received.

• Avoid reflecting bolt ends not perpendicular to the

axis of the bolt. Sonic energy will be reflected

toward the sidewall of the bolt.

• Avoid non parallel reflecting bolts ends due to

bending of the bolt.



Transducer BeamSpread• The energy beam produced by a transducer

spreads out as it propagates through the material

– this phenomenon is referred to as beam spread

or ultrasonic diffraction.

• Beam spread occurs because as the wave

travels through the material the energy transfer is

from particle to particle – if the particles are not

directly aligned in the direction of the wave

propagation then a portion of the energy is

transferred at an angle.

• Beam spread is largely determined by the

frequency and diameter of the transducer.

2 MHz Frequency

5 MHz Frequency

9 MHz Frequency



Transducer BeamSpread

• Spread is greater in lower frequencies than

higher frequencies.

• Additionally as the diameter of the transducer

increases beam spread is reduced.

• Beam spread is an important consideration for a

couple of reasons – firstly spread lowers the

amplitude of reflections thereby making the

return signal weaker.

• Secondly beam spread may result in difficulty

interpreting the return wave due to reflections

from the bolt sides causing noise.

2 MHz Frequency

5 MHz Frequency

9 MHz Frequency



Transducer Selection

• Correct transducer selection is important because as we

have just covered the lower the frequency of the pulse the

greater the beam spread.

• However as sound waves travel through a medium they lose

energy to the medium and are damped.

• This is due to the molecules generating heat as they are

forced to vibrate back and forth to transmit the wave.

• Therefore a sound wave can only propagate through a

limited distance.

• Based on this lower frequency waves will travel further

because less energy is transferred to the medium.

• Note that although damped waves have decreasing

amplitudes, their frequency is unaffected.



Temperature Compensation

• As the temperature in a material increases two things happen to that material.

• Firstly there is a physical increase in length.

• Secondly the particles within the material start to vibrate more.

• This vibration makes it harder for the ultrasonic pulse to penetrate the material – meaning the

pulse travels slower - effectively increasing the ultrasonic length.

• The increase in ultrasonic length happens at a greater rate than the physical change in

length.

• For the purposes of the Echometer these two factors are combined into a single value known

as the Temperature Coefficient.

• If the Echometer is to be used as a one time validation check then temperature compensation

does not need to be considered – this is more critical to in service monitoring.



Thank You We look forward to further discussions on our portfolio and to serve you in

the near future.

Warm regardsMurali Narasimhan (Managing Partner)[email protected] : +91-9902783547Coretech Industrial Solutions#202A, Brigade MM Annex Block, K.R Road,7th Block Jayangar, Bengaluru -560070Website : www.coretechindustrial.in


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Echometer Ultrasonic Bolt load measurement System By BOLTIGHT

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