Eddy Current's Report

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31/05/2010

Objectives

The objectives are to identify Materials, to detect surface defects on a collection of samples and the thickness of the coating of paint on a bracket using the Eddy Current and a Magnetic coating thickness gauge.

Abstract

First is to categorize the different metals being tested by using eddy current method. A collection of metals are to be tested.

The second was Flaw detection testing by using eddy current method using two types of probe. The first Probe to be used is a Needle absolute indicator, the second a Probe Reflection.

The sample under examination is constructed with different imperfections on its surface. The output signals from the two probes are to be compared.

The last one is the testing of thickness of paint on iron by using eddy current method. In this testing the thickness of the coat varied between 59-94 microns.

In all testing, differences of the signal testing are compared to analyze.

Introduction

Eddy currents are created through a process called electromagnetic induction. The Eddy-current instrument uses this process to detect flaws in conductive materials.

Eddy currents are fields of alternating magnetic current. When the probe is linked with the sample under inspection, the alternating magnetic field induces eddy currents in the test part.

These eddy currents can be monitored. The property variations and any flaws will cause a change in eddy current flow in the sample. The defects will be detected by the probe and read by the meter.

One of the major advantages of eddy current is the variety of inspections and measurements that can be performed. Eddy currents can be used for Crack detection, material thickness measurements, coating thickness measurements and material identification. [pic]

Procedures

[pic]

fig.1.

HOCKING LOCATOR 2

Using eddy current an optimal frequency for the metal testing instrument is to be found. The testing instrument consists of a range of frequencies between of 6-100 kHz, and a 50 ohms sensor circuit in the Probes we connected to the meter.

Connect Probe to Eddy-current meter. Turn power on, adjust to desired settings. Clean contact surfaces and place probe on to the known stamped samples to determine if the Eddy-current is correct in its readings. Now that the Eddy current is proved to be an accurate instrument progressing with further testing may go ahead. The probe is to be placed on the unidentified samples. The readings are fed back to the meter to identify materials. Document the results.

To detect defects on the surface of our sample we will use two different probes. First we connect the needle absolute indicator to the Hocking Locator (fig.1.). Gently glide the probe across the test piece. The readings are sent back to the meter. The findings are to be recorded. Connect the probe reflection to the meter. Again slowly move the probe along the sample. Take note of the results.

[pic]

fig.2.

Rollback dial Magnetic Thickness gauge

A magnet is attached to one end of a pivoting balanced arm and connected to a calibrated hairspring. By rotating the dial with a finger, the spring increases the force on the magnet and pulls it from the surface. These gauges are easy to use and have a balanced arm that allows them to work in any position, independent of gravity. Typical tolerance is ±5%.

Place the magnetic thickness gauge (fig.2.) on each of the seven points along the brackets surface and zero the gauge. Gently roll back the dial until the magnet is pulled from the surface. Read the gauge and document each measurement before moving on to the next...
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