User`s manual

7800 Series Hysteresisgraph System User's Manual
Obtaining Measurement Repeatability C-3
Sample (Continued)
(2) To eliminate this effect, it is advisable to center the sensor vertically in the electromagnet airgap.
(a) This always results in the center-plane of the magnet being tested, reducing bias in the test due
to manufacturing density/gradient effects.
(b) Although repeatable, a bias may still be introduced in the measurement.
(c) This may not result in an average of hot and cold flux densities, but merely in a repeatable value
somewhere in-between.
5. Sample position in airgap.
a. Samples should be inserted into the center of the poletip (except side-by-side and embedded coils).
b. Orient sample identically each time.
(1) Circular sample should have an angular reference mark and be placed in the coil set at the same
angle each time.
(2) Rectangular samples should also be placed in with a known cross-sectional orientation.
(3) Samples should not be placed into the coil set randomly. Top, bottom, sides, angle should all be
known and replicated with each measurement.
C5.0 STANDARDS
High-Purity Nickel Reference Standards are used for their magnetic and geometric similarities to the samples to be
tested.
1. Temperature should be monitored and a temperature-compensated value of saturation induction should be
entered into the system for calibration.
2. All issues related to sample/coilset relationships also apply for the standard/coilset relationship.
3. The geometry of the standard should closely approximate the geometry of the samples to be tested.
a. Standard cross-section should be ±20% of sample cross-section.
b. Standard magnetic length should be within ±30% of sample magnetic length.
c. For shorter samples, it is more important to use similar heights as the standard’s self-demagnetizing
field’s will become a more significant effect.
4. Care must be taken not to damage the mechanically soft Nickel standard.
a. Check Standard dimensions with a micrometer before and after each use to verify they are identical to
historical data.
b. If the dimensions have changed significantly, the standard should be returned to the factory for re-work.
C6.0 POLE-TIP GEOMETRY AND CONDITION
1. Poletips should be inspected for condition before each calibration.
a. Check for debris.
b. Check for impacted areas and poleface surface imperfections.
(1) Surface imperfections will increase the reluctances between the sample and the polefacecs which
leads to error in the measurement.
c. Check for non-parallelism between the two polefaces.
(1) Non-parallelism results in variable H field distribution.
d. Check for residue form the cleaning/resurfacing process.
2. Poletips should be cleaned as necessary.
a. Immediately after a sample has broken in the airgap.
b. Whenever there is a chance of contamination of the face of the pole tip.
c. Samples placed on the poletip should also be cleaned before measurement to ensure no sample chips or
fragments are present during the test.
(1) These fragments may embed into the poleface and contaminate it permanently until the poleface is
resurfaced.