Sound is created by vibrations and it can be something we want such as music, which means it's intentional. But sound can also be noise, or something that needs to be reduced or eliminated. This is often the case in the manufacturing industry where vibration analysis often signifies imbalance in a machine's moving parts or uneven friction and can imply wasted energy, leading to the machine's breakdown. There are generally two types of measuring instruments that can quantify vibration. Specific designs of these instruments would vary depending on the field of study and application.
The following will show you how to measure vibration:
1. Measuring with velocity pickups.
Velocity pickups give out an electrical signal that is relative to the speed of the vibration occurring in the machine being tested. The speed is cyclic because it repeats within a given period of time. Velocity pickups therefore express the measurement in milli-volts per centimeter per second. An increasing voltage that shows up on the velocity pickups display panel indicates an increasing speed of vibration in the machine under evaluation.
Velocity pickups are designed to measure vibration frequencies that are higher than their own natural frequency. They are mounted on the machine to be tested by simply attaching it to the surface. Several methods for attaching these monitoring instruments are used. Silicon grease is often used and reliable. Magnets are also utilized, but this way of attaching the instrument has the disadvantage of having a small usable frequency range. Magnetic mounts have their own significant mass and spring-like qualities, and are positioned between the velocity pickup and the vibrating surface. These naturally affect the accuracy of the measurements.
The positive characteristics of velocity pickups as a vibration measuring instrument are its sensitivity and ability to withstand most harsh industrial environments. Speed is a dependable determining factor of the severity of an occurring vibration. The downside with these instruments is that it can be affected by magnetic fields, which are often generated by large machines powered by alternating current electricity.
2. Measuring with accelerometers.
An accelerometer's output electrical signal indicates the acceleration of the vibration on the tested machine. The basic design of this measuring instrument involves a damped mass loaded on springs. When vibration is carried over to the accelerometer instrument, the damped mass is displaced until the springs compensate for the force of the vibration. The amount of displacement determines the amount of acceleration.
Its advantage over velocity pickups are its lighter weight, smaller size, and wider range of frequency sensitivity. Furthermore it can measure vibration at a specific point without the instrument being directly attached to the surface. Although it is primarily designed to measure acceleration, the vibration measurement instrument can be easily configured to also measure speed.
Velocity pickups and accelerometers are classified as transducers. Transducers are a type of machine that can convert mechanical energy to electrical energy. The mechanical energy is supplied by the vibration, and the resulting proportional electrical energy is the measuring standard.