Lake Shore Model 421 Gaussmeter User’s Manual
Operation
3-13
3.16 PROBE CONSIDERATIONS
To avoid damage and for best results during use, the probes have a number of handling and accuracy
requirements that must be observed. Changing probes is discussed in Paragraph 3.16.1. Probe
handling is discussed in Paragraph 3.16.2. Probe operation is discussed in Paragraph 3.16.3. Finally,
accuracy considerations are provided in Paragraph 3.16.4.
3.16.1 Changing Probes
A 512-byte Electrically Erasable Programmable Read Only Memory (EEPROM) is included in each
probe. The EEPROM stores specific information that the gaussmeter requires for operation. The
information includes serial number, probe sensitivity, and field compensation data.
CAUTION:
The probe must be connected to the rear of the instrument before applying power
to the gaussmeter. Probe memory may be erased if connected with power on.
When the instrument is powered up, the probe memory is downloaded to the gaussmeter. This is how
the gaussmeter knows which ranges are available and which error correction to apply. To change
probes, first turn power off, remove the existing probe, and then plug in the new probe. When power
is restored, the characteristics of the new probe are downloaded to the gaussmeter memory. Normal
operation may continue after the new probe offset is nulled using the Zero Probe operation.
If the instrument is powered up with no probe attached, the following message is displayed.
* * NO PROBE * *
Power off,attach
3.16.2 Probe Handling
Although every attempt has been made to make the probes as sturdy as possible, the probes are still
fragile. This is especially true for the exposed sensor tip of some transverse probes. Care should be
taken during measurements that no pressure is placed on the tip of the probe. The probe should only
be held in place by securing at the handle. The probe stem should never have force applied. Any
strain on the sensor may alter the probe calibration, and excessive force may destroy the Hall
generator.
CAUTION:
Care must be exercised when handling the probe. The tip of the probe is very
fragile. Stressing the Hall sensor can alter its calibration. Any excess force can
easily break the sensor. Broken sensors are not repairable.
Avoid repeated flexing of the stem of a flexible probe. As a rule, the stem should not be bent more
than 45° from the base. See Figure 3-4. Force should never be applied to the tip of the probe. On all
probes, do not pinch or allow cables to be struck by any heavy or sharp objects. Although damaged
or severed cables should be returned to Lake Shore for repair, please understand that probes are not
always repairable.
When probes are installed on the gaussmeter but not in use, the protective tubes provided with many
probes should be placed over the probe handle and stem in order to protect the tip. When the
gaussmeter is not in use, the probes should be stored separately in some type of rigid container. The
cardboard and foam container that Lake Shore probes are shipped in may be retained for probe
storage. For further details on available accessories and probes, refer to Chapter 5.
