Condition monitoring

Rishi Sharma 09408EN003

INTRODUCTION• Condition monitoring (CM) is a process of monitoring a

parameter of condition in machinery eg . Vibration , temprature etc

• In order to identify a significant change which is indicative of developing a fault .

• Condition monitoring is a process which is used to monitor the condition of the machine which ultimately reduces the time required to identify and rectify the fault which further increases the efficiency of the machine.

• Condition monitoring provides us the real time information about the condition of the machine which gives us the ability to minimize or to eliminate the factors responsible for occurrence of faults .

Types of condition monitoring

• Vibration condition monitoring • Lubricant analysis • Acoustic emission• Infrared thermography • Ultrasound emission

Vibration condition monitoring• Machine vibrations, also called chatter, correspond to the relative

movement between the work piece and the cutting tool. The vibrations result in waves on the machine surface. This affects typical machining processes, such as turning , milling , drilling, and grinding.

VIBRATION SENSORAccelerometers are transducers for measuring the dynamic acceleration of a physical device. The most common accelerometer measures acceleration only along a single axis. This type is often used to measure mechanical vibration levels. The second type is the triaxial accelerometer. This accelerometer is used to determine the type of vibration or the direction of acceleration.

Accelerometers designed to measure vibration are based on the piezoelectric effect. In a piezoelectric accelerometer, a mass applies force to a crystal creating a high-impedance charge, which results in a voltage across the crystal.

Piezoelectric accelerometers require an external amplifier to amplify the charge easier to use accelerometers recommended for typical measurements include an integrated amplifier. These sensors are referred to as integrated electronic piezoelectric (IEPE) sensors.

Lubricant analysis 

• Oil analysis (OA) is the laboratory analysis of a lubricant's properties, suspended contaminants, and wear debris. OA is performed during routine preventive maintenance to provide meaningful and accurate information on lubricant and machine condition. By tracking oil analysis sample results over the life of a particular machine, trends can be established which can help eliminate costly repairs.

OA can be divided into three categories:• analysis of oil properties including those of the base oil and its

additives,• analysis of contaminants,• analysis of wear debris from machinery,

Acoustic emission• Acoustic emission (AE) is the phenomenon of radiation of acoustic

(elastic) waves in solids that occurs when a material undergoes irreversible changes in its internal structure, for example as a result of crack formation or plastic deformation due to aging, temperature gradients or external mechanical forces.

• In particular, AE is occurring during the processes of mechanical loading of materials and structures accompanied by structural changes that generate local sources of elastic waves. This results in small surface displacements of a material produced by elastic or stress waves generated when the accumulated elastic energy in a material or on its surface is released rapidly.

• The waves generated by sources of AE are of practical interest in methods used to capture AE in a controlled fashion, for study and/or use for inspection of structural integrity, quality control, system feedback, process monitoring, and others.

How to use AE• The application of acoustic emission to non-destructive testing of materials,

typically takes place between 100 kHz and 1 MHz Unlike conventional ultrasonic testing, AE tools are designed for monitoring acoustic emissions produced within the material during failure or stress.

USES• To study the formation of cracks during the welding process, as opposed to

locating them after the weld has been formed.• In a material under active stress, such as some components of an airplane during

flight, transducers mounted in an area can detect the formation of a crack at the moment it begins propagating.

• A group of transducers can be used to record signals, then locate the precise area of their origin by measuring the time for the sound to reach different transducers.

• The technique is also valuable for detecting cracks forming in pressure vessels and pipelines transporting liquids under high pressures. Also, this technique is used for estimation of corrosion in reinforced concrete structures

Infrared thermography

Thermal images, are actually visual displays of the amount of infrared energy emitted, transmitted, and reflected by an object.The image shows the viewer an approximation of the temperature at which the object is operating, the camera is actually using multiple sources of data based on the areas surrounding the object to determine that value rather than detecting the actual temperature.This phenomenon may become clearer upon consideration of the formula

Incident Energy = Emitted Energy + Transmitted Energy + Reflected Energy

• Incident Energy is the energy profile when viewed through a thermal imaging camera.

• Emitted Energy is generally what is intended to be measured.• Transmitted Energy is the energy that passes through the

subject from a remote thermal source.• Reflected Energy is the amount of energy that reflects off the

surface of the object from a remote thermal source.• If the object is radiating at a higher temperature than its

surroundings, then power transfer will be taking place and power will be radiating from warm to cold.

• We can use thermal imaging camera to take the picture of the object and it will build a picture in the viewer and record a visible picture, usually in a JPG format.

Thermal imaging of electrical fuse block

• This functionality makes the thermal imaging camera an excellent tool for the maintenance of electrical and mechanical systems in industry and commerce. By using the proper camera settings and by being careful when capturing the image, electrical systems can be scanned and problems can be found

Ultra Sound EmissionUltrasound transducers are used to convert an electrical signal into ultrasonic energy that can be transmitted into the object to be monitored, and to convert ultrasonic energy reflected back from the object into an electrical signal.

The general composition of an ultrasound transducer is shown below• the most important component is a thin piezoelectric (crystal)

element located near the face of the transducer• the front and back face of the element is coated with a thin

conducting film to ensure good contact with the two electrodes• the outside electrode is grounded to protect the patient from

electrical shock• an insulated cover is used to make the device watertight• an acoustic insulator made of cork or rubber is used to prevent the

passing of sound into the housing (i.e. reduces transducer vibrations).

• the inside electrode is against a thick backing block that absorbs sound waves transmitted back into the transducer

How to create an ultrasound wave using Piezoelectric crystal

• When a positive voltage is applied across the surface of the crystal, it creates an electric field across the crystal surface which cause the molecules (dipoles) in the crystal to realign and thus changing the shape (width) of the crystal.

• When the voltage polarity is changed from positive to negative, there is a point in time when the electric field across the crystal is zero (at voltage equal to zero) and the crystal relaxes . When the voltage polarity is reversed (i.e.: negative) the crystal realigns once again and changes its width once again .

• The net effect the alternating voltage pulse has on the crystal is to make it oscillate back and forth about its width. This change in shape of the crystal increases and decreases the pressure in front of the transducer, thus producing ultrasound waves.