Magnetic Instrumentation 2130, Инструкция по эксплуатации

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CHAPTER 4 MEASUREMENT CONSIDERATIONS
4-4
4.5.2 Maxwells
The Maxwells unit is identical to Maxwell-Turns, with the exception that the measurement
result is already divided by the number of turns entered in the Model 2130’s coil parameter
menu.
4.5.3 Gauss
The Gauss is the cgs unit for of flux density. It is defined as 1 Maxwell per cm
2
. To use this
measurement unit, both the number of turns, and the coil area must be entered into the Model
2130’s coil parameter menu. The shape and area of the sample must be very close to those
of the search coil.
4.5.4 Tesla
The Tesla is the SI unit for flux density. It is defined as 1 Weber per m
2
(1 Weber = 10
8
Maxwells, 1 Tesla = 10
4
Gauss).
4.5.5 Bdi-Gauss
The Bdi-Gauss is a measure of the intrinsic remanent induction in a magnet sample. This unit
should only be selected when the Model 2130 is used in conjunction with a Helmholtz coil.
The Helmholtz constant for the coil and the volume of the magnet sample must be known, and
entered into the coil parameter menu.
4.5.6 Bdi-Tesla
The Bdi-Tesla unit is similar to the Bdi-Gauss unit except that the unit for induction is in Tesla
instead of Gauss.
4.6 Selecting a Search Coil
One of the real advantages of a fluxmeter is its ability to use almost any coil of wire as a
sensor. However, the user should consider several parameters when deciding on the search
coil for a particular application.
4.6.1 Number of Turns
The output voltage from a search coil for a given change in flux is directly proportional to the
number of turns it contains. Since the Model 2130 readout is usually more stable as the range
is increased, there is a definite advantage to having a large number of turns in the search coil
when measuring a small change in flux, and a smaller number of turns when measuring a
large change in flux.
4.6.2 Coil Resistance
Unfortunately, as the number of turns in a coil increases, so does its resistance. As the coil
resistance increases, the signal strength seen by the Model 2130 decreases. As long as the
coil resistance is known, the user may enter this value using the Model 2130’s menu system.
In this case, the fluxmeter will automatically compensate for the loss in sensitivity. As a
general rule, though, the coil resistance should not exceed approximately 10% of the Model
2130’s input impedance for a given range. This is due primarily to the temperature coefficient
of the coil resistance. In other words, the Model 2130 can compensate for a large coil
resistance, however if the resistance changes, the compensation the fluxmeter applies will no
longer be correct. The following table indicates the Model 2130 input impedance for each
range, and the maximum recommended coil resistance.