Harmonic line noise correction for electron energy loss spectrometer
AssigneeGatan, Inc.
InventorColin Trevor
Life of this patent
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Abstract
Electron Energy Loss Spectrometer including a correction circuit for fundamental and third harmonic line noise is described. Various circuits for creating the correction signals are also described. A method of correcting for fundamental and third harmonic line noise is also described.
Claims20
An electron energy loss spectrometer (EELS) operating from an alternating current (AC) power line voltage having an AC power line fundamental frequency comprising:
- a bending magnet for producing a spectrum of electron energy levels;
- a direct current bending magnet field excitation source;
- and
- a power line noise correction circuit configured to produce a first correction signal at the fundamental AC power line frequency and a second correction signal at a harmonic of the fundamental AC power line frequency.
An alternating current (AC) power line noise correction circuit for producing a correction signal comprising a fundamental AC power line frequency signal and a harmonic of the fundamental AC power line frequency signal, comprising:
- a line voltage sensor configured to produce a line voltage signal;
- an analog to digital (A/D) signal converter;
- a microcontroller having a program memory and a read/write buffer memory;
- and
- a digital to analog (D/A) signal converter;
- wherein said microcontroller is configured to
- sample said line voltage signal at a sample rate,
- store samples of said line voltage signal in said read/write buffer memory,
- read out said samples of said line voltage signal from said read/write buffer memory to create a first read out at said AC power line frequency and a second read out a harmonic of said AC power line frequency,
- combine said first and second readouts to produce a combined output value, and
- output said combined output value to said D/A converter to produce a combined correction signal.
A method of correcting for AC mains noise in an electron energy loss spectrometer (EELS) comprising the steps of:
- sampling an AC power line voltage,
- adjusting amplitude and phase of the AC power line voltage to create a fundamental frequency correction signal,
- generating a signal at a harmonic of the AC powerline voltage,
- adjusting amplitude and phase of said signal at the harmonic of the AC powerline voltage to create a harmonic correction signal and
- applying said fundamental and said harmonic correction signal to a bending magnet in the EELS).
Dependencies are inferred from the claim text.