Lake Shore Model 421 Gaussmeter User’s Manual
Accessories and Probes
5-3
5.2 LAKE SHORE STANDARD PROBES
In addition to the probe included with the purchase, additional probes are available for use with the
Model 421 Gaussmeter. Examples include Axial, Flexible Axial, Transverse, Flexible Transverse,
Robust Transverse, Tangential, and the Gamma Probe. Because the Model 421 covers such a wide
magnetic field range (0.01 mG to 300 kG), three probe ranges are available: High Stability (HST), High
Sensitivity (HSE), and Ultra-High Sensitivity (UHS). Please consult the factory for availability of probe
types not detailed in these figures. Information on Hall generators is presented in Appendix C.
5.2.1 Probe Selection Criteria
Some guidelines are provided below to aid in the selection of a probe for you application.
1. Choose a probe to match the application. Do not buy more accuracy, field range, or fragility than
is actually necessary.
2. The thinner a probe, the more fragile it is. Try to avoid the temptation to select an easily damaged
probe based on a possible, but not probable, future application. For instance, avoid using an
exposed-device probe such as a Model MFT-3E03 or MNA-1904 type for general field
measurements.
Once a stem or sensor has been damaged, the probe is not repairable.
3. Metal enclosed probes, such as the Model MMT-6J08 and MMA-2508 types, offer the greatest
amount of protection to the Hall sensor, and therefore are the most rugged types.
4. Be cautious about using aluminum stemmed, transverse probes, such as the Model MMT-6J08
type, where AC magnetic fields are to be measured. Eddy currents in the stem material can affect
reading accuracy. A superior choice for AC measurements would b the Model MNT-4E04 type
fiberglass-epoxy stem probes.
5. Several stem lengths are offered for each probe type. User preferences or test set-up dimensions
usually determine the final selection. Longer stems are more susceptible to accidental bending
(in many cases not catastrophic, but bothersome). Stem length does not affect performance.
6. Be aware of the differences in the probe “active areas” shown on the data sheet. A Hall effect
probe will indicate the average field value sensed over that total active area. Thus, when
measuring magnetic fields with a high gradient across the sensor width, choose the smallest
active area practical (keeping in mind, however, the fragility rule in number 2 above).
7. Lake Shore gaussmeter probes exhibit different ranges of magnetic fields over which they will
provide valid readings. Check the specification sheet for these usable ranges. High Stability
probes, such as those whose model numbers end in -VG, are usable on full scale ranges of
300 gauss (30 millitesla) to 30 kilogauss (3 tesla). The High Sensitivity family of probes
(i.e., -VH models) can be used on 30 G (3 mT) to 30 kG (3 T) full scale ranges. High field probes
are specially calibrated to provide use above 30 kG (3 T), and the Gamma Probe operates on the
300 mG (30 µT) and 3 G (300 µT) ranges.
8. If none of the standard probe configurations seem to fit your needs, always remember that Lake
Shore can provide custom probes to meet your physical, temperature, and accuracy
requirements. Contact Lake Shore with details of your special requirements.
5.2.2 Radiation Effects on Gaussmeter Probes
The HST and HSE probes use a highly doped indium arsenide active material. The HST material is
the more highly doped of the two and therefore will be less affected by radiation. Some general
information relating to highly doped indium arsenide Hall generators is as follows:
• Gamma radiation seems to have little effect on the Hall generators.
• Proton radiation up to 10 Mrad causes sensitivity changes <0.5%.
• Neutron cumulative radiation (>0.1 MeV, 10
15
/sq. cm.) can cause a 3 to 5% decrease in sensitivity.
• In all cases the radiation effects seem to saturate and diminish with length of time exposed.
