Hitachi S-4800 manual Stray Magnetic Field

1.1.6Stray Magnetic Field

You should measure the stray magnetic field at the place for installing the Model S-4700 in advance. When the requirements given in Table 1-1 are satisfied, no image trouble will occur. Avoid locations at which abrupt electric current change or magnetic field change might occur due to the presence of a large-sized magnetic clutch or power cable for other equipment.

Table 1-1 Stray Magnetic Field (at image recording)

				Frequency	Frequency
				Component	Component
	Acceleratin	Working		Synchronous	Asynchronous	Change with
			Magnification	with Power	with Power
	g Voltage	Distance				Time (drift)
				Supply AC	Supply DC
				Magnetic Field	Magnetic Field
				(effective value)	Fluctuation
				290 nT	320 nT	600 nT/min
Allowable						(horizontal)
	15 kV	4 mm	220,000×	(horizontal)	(horizontal)
value						450 nT/min
				220 nT (vertical)	240 nT (vertical)
						(vertical)
				150 nT	170 nT	310 nT/min
						(horizontal)
	1 kV	1.5 mm	120,000×	(horizontal)	(horizontal)
						280 nT/min
				130 nT (vertical)	150 nT (vertical)
						(vertical)
					nT:	Nanotesla

NOTICE: 1. The frequency component synchronous with power supply (AC magnetic field) is an effective value. Therefore, its allowable value should be increased to 2.8 times for evaluation in terms of p-p (peak to peak) value.

2.The DC magnetic field fluctuation stands for a rapid change of stray magnetic field with time lapse. A gradual and moderate change with time lapse is handled as a temporal variation (drift).

3.The temporal variation (drift) of stray magnetic field signifies a difference (maximum drift) between the maximum and minimum levels within the specified time (1 minute).

4.The allowable value of AC magnetic field is determined so that image distortion (elongation, contraction or curving) at the specified magnification will not exceed

0.5mm.

5.The allowable value of DC magnetic field fluctuation is determined so that image disturbance (image shift or spike noise) at the specified magnification will not exceed 0.2 mm on a micrograph.

6.The allowable value of temporal variation (drift) in stray magnetic field is determined so that image sway due to that temporal variation will not exceed

0.5mm on a micrograph taken at the specified magnification.

7.Fluctuation-free DC component (excluding terrestrial magnetic field) of stray magnetic field will not cause the electron beam to sway. Therefore, image

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