Lake Shore Model 420 Gaussmeter User’s Manual
Operation
3-5
3.10 LOCKING AND UNLOCKING THE KEYPAD
The Model 420 front panel keypad may be locked, preventing
unauthorized changes to the settings. To lock the keypad,
press and hold
Max Hold
(about 10 seconds) until the
display to the right appears.
To unlock the keypad, press and hold
Max Hold
(about 10
seconds) until the display to the right appears. The keypad
unlocks and the display reverts to the normal display.
3.11 FACTORY DEFAULT SETTINGS
To return the instrument to factory default settings, press and hold
Max Reset
for about 20 seconds:
Max Hold:
Off
Auto Range:
Off
Relative:
Off
Interface:
300
Range:
Highest range for probe
AC/DC:
DC
Gauss/Tesla:
Gauss
Keypad:
Unlocked
Other gaussmeter calibration information and probe data are not affected by this reset. Zero the probe after
completing this operation.
3.12 PROBE CONSIDERATIONS
This section covers several probe concerns to avoid damage and yield the best results: Changing Probes
(Paragraph 3.15.1), Probe Handling (Paragraph 3.15.2), Probe Operation (Paragraph 3.15.3), and Accuracy
Considerations (Paragraph 3.15.4). For details of available Lake Shore Probes, see Paragraph 6.2.
3.12.1 Changing
Probes
CAUTION: Connect the probe to the unit rear before applying power to the gaussmeter. Probe
memory may be erased if connected with power on.
Each probe includes a 512-byte Electrically Erasable Programmable Read Only Memory (EEPROM). The
EEPROM stores specific information the gaussmeter requires for operation. The information includes serial
number and probe sensitivity, and may also include field and temperature compensation data.
Upon power up, probe memory downloads to the gaussmeter. Probe memory includes available ranges and
which error correction to apply. To change probes, first turn power off, remove existing probe, then plug in the
new probe. When power is restored, the new probe
characteristics download to the gaussmeter and normal
operation may continue. If the unit powers up with no probe
attached, the message to the right displays.
3.12.2 Probe
Handling
CAUTION: Take care when handling the probe; the tip is very fragile. Stressing the Hall sensor can
alter its calibration. Any excess force can easily break the sensor. Broken sensors are irrepairable.
Although probes are designed as sturdily as possible, they are still fragile. This is especially true for the
exposed ceramic tip of transverse probes. Take care to place no pressure on the ceramic tip during
measurements. Secure the probe in place only at the handle. Never apply force to the probe stem. Any strain
on the ceramic substrate may alter the probe calibration, and excessive force may destroy the Hall sensor.
Avoid repeated flexing of the sensor mounted at the end of a flexible stem. As a rule, do not bend the stem
more than 45° from the base (see Figure 3-3). Never apply force to the tip of the probe. On all probes, do not
pinch or allow cables to be struck by heavy or sharp objects. Although Lake Shore repairs damaged or
severed cables that are returned, probes are not always repairable.
When probes are installed on the gaussmeter but not in use, place the protective tube provided with many
probes over the probe handle and stem to protect the tip. When the gaussmeter is not in use, store probes
separately in some type of rigid container, preferably the cardboard and foam container in which Lake Shore
probes ship. For details on available accessories and probes, see Chapter 6.
L o c k K e y p a d
U n lo c k K e y p a d
* * N O P R O B E * *
P o w e r o f f ,a t t a c h
Summary of Contents for 420
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