A Guide to Selecting Isolation Systems for Measurement and Analysis Instruments

In physical science, isolation is defined as the process of preventing the transmission of unwanted noise into a system. Isolation can be applied to different types of environmental noise which can interfere with processes and measurements.

Simple vibration isolation systems include a damper, a spring and mass. Electromagnetic isolation systems, however, features field generation devices and highly sophisticated sensors to prevent electromagnetic interference (EMI).

When selecting an isolation system, it is important to take into account certain physical processes such as transmissibility, damping and resonance. A resonance occurs when the displacement of a structure is greater than the input displacement during oscillation. Damping takes place at the reduction of resonance amplitude. Transmissibility is a quantity of response of an isolator.

Characteristics of Isolator Systems

Isolators are manufactured in a wide range of weights, sizes and shapes. Firstly, the weight of the instrument to be isolated should be determined. Based on this, the isolation system with sufficient load capacity to withstand this weight can be selected. It is also essential to measure the dimensions of the instrument such that it fits correctly into the isolation system during isolation.

Isolation systems with wider bases should be used if the centre of mass is located above the instrument structure, in order to ensure stability. The performance of the isolator can be easily regulated for a smaller area and mass.

Positioning of the sensitive elements of isolation system near a large or complex component reduces the introduction of noise and resonances. Another important consideration is the access points that avoid the interference with service access or sample loading.

Sensitivity of Isolator Systems

The sensing mechanism of each instrument is subjected to specific noise levels. In addition, each instrument consists of a mechanical structure and inherent resources that affect the noise transmission. The sensitivity of the instrument can be determined by consulting the allowable noise specifications developed by the manufacturer, using the installation requirements document or the instrument manual, or directly consulting the manufacturer.

Most of the sensitivity information can be obtained with respect to the precision level at which the instrument is operating. For instance, imaging instruments operating at nano level are highly sensitive to environmental noise. Instruments operating at its maximum precision level will be sensitive than one operating within its range of capability.

Trial-and-error test method is the only way to determine the frequency of vibration measurement equipment when lacking input from the instrument manufacturer.

Challenges Involved in Selecting Isolator Systems

Each environment has different mechanical characteristics and noise sources. The operational sensing mechanisms, in addition, will exhibit own sensitivities to certain vibration levels. In general, noise levels and instrument sensitivity are the two major factors to be considered in characterizing an isolation requirement. These parameters are hard to determine with great accuracy.

In some cases, despite of great care considered in selecting the isolation system, it is difficult to determine the way in which the given set-up is affected. Besides all this, choosing an instrument which best suits the application is a critical step, which can be carried out by testing the isolation system in the appropriate facility, with the instrument-to-be isolated.

Passive Vibration Isolation Systems

Passive vibration isolation systemsare designed with a spring placed between the sensitive piece of equipment and incoming vibrations. These systems are insensitive to noise levels and provide isolation with respect to their mechanical characteristics.

In most cases, isolators are soft materials such as rubber or sorbothane sandwiched between two rigid surfaces. This design combines both isolation and damping properties. Metal spring is another simple isolator which does not exhibit damping characteristic, but is effective at shifting resonances of machinery to avoid negative influences on nearby equipment. Bungees, however, provide isolation by shifting the resonances to frequencies having less effect on the instrument.

The air-based isolation system is one of the most common isolation systems that are used along with precision instruments that operate by supporting a mass. Figure 1 shows a typical example of passive vibration isolation system.

Laser Particle Analyzer installed on DT Air-based Isolation

Figure 1. Laser Particle Analyzer installed on DT Air-based Isolation

Active Vibration Control Systems

Active vibration control systems, also known as active vibration cancellation or active vibration isolation are isolation systems which react to incoming vibrations. They are of two types: feedback and feed-forward systems. Feed-forward systems are programmed to compensate for regular periodic vibrations. Feedback systems, however, continuously sense and react to incoming vibrations. Figure 2 shows a typical model of an active vibration control system.

Desktop Ultramicrotome with TS Compact Desktop Active Vibration Control System

Figure 2. Desktop Ultramicrotome with TS Compact Desktop Active Vibration Control System

About Herzan

Herzan provides high performance environmental solutions for precision research instruments. They include acoustic enclosures, vibration isolation systems, Faraday cages, and site survey tools. Herzan specializes in supporting nanotechnology research, but also offers solutions for product testing, in-vitro fertilization, and many other applications.

Herzan understands that every application and environment is different, so it collaborates with customers to create comprehensive integrated solutions that satisfy their unique demands.

Herzan was founded in 1992 by Ann Scanlan in Orange County, California. Originally, Herzan was established as an American subsidiary of Herz Company Ltd., a Japanese company specializing in vibration control. The name Herzan comes from the amalgamation of 'Herz' and 'Ann'.

This information has been sourced, reviewed and adapted from materials provided by Herzan.

For more information on this source, please visit Herzan.

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