• A current transformer (CT) to sense the signal.
• Appropriate signal conditioner for subsequent signal analysis.
• Analysis of the signal via an FFT digital signal processor to present the "Current Spectrum"
• Presentation of current signature patterns indicative of faults and identification of the problem.

Current Transformer	Spectrum Analyser	Current Signature

• The current signal to the motor is analysed to produce a current spectrum - normally referred to as a Current Signature.
• The objective is to produce a current signature to identify the magnitude and frequency of each individual component that constitutes the current signal to the motor.
• Current signature patterns can be identified for healthy and unhealthy motors and to detect specific faults.
• In the current spectrum a wide dynamic range in dB (for current scale) is used since components indicative of faults can be much smaller than the main supply frequency component of current.

Time Domain Current Signal	Time Domain Current Signal
Current Spectrum - dB (amps) v. Frequency	Current Spectrum - dB (amps) v. Frequency

Question: If the time domain current signal has a fundamental of 60Hz and also includes 5th, 7th, 11th and 13th harmonics sketch the Current Spectrum:

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EM Diagnostics Ltd,
20 Greystone Road,
Alford, Aberdeenshire, AB33 8TY
Scotland, UK