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Lake Shore Model 480 Fluxmeter User’s Manual
5-10 Advanced Operation
5.9 DRIFT ADJUSTMENT
Drift Adjustment is a fact of life when making DC and DC Peak measurements with an analog integrator
like the one in the Model 480. Drift is caused by offsets present in the integrator components and coil
connections. AC and AC Peak measurements do not require drift adjustment because modifications to
the integrator bring the reading to zero when no signal is present.
Drift is related to instrument hardware and often temperature change. The Model 480 has been
designed to minimize drift but there are some important things to do during setup when low drift is
important.
1. Let the instrument warm up before attempting to adjust drift. Allow 30 minutes for normal use and
longer if the instrument is stored in an unheated area.
2. Attach the coil that will be used with the fluxmeter before drift is adjusted.
3. Make sure coil connections are tight.
4. Keep coil leads as short as possible and have as few connections as possible.
5. Shield coil contacts from fast temperature changes.
The Model 480 has replaced the drift adjustment trim-potentiometer present on older fluxmeters with
two internal digital-to-analog converters (DACs) for drift compensation. These converters can be set
from the keypad for very precise manual drift adjustment or controlled by the instrument for hands off
drift adjustment. The paragraphs below describe three ways to adjust drift with the Model 480. All drift
adjustments must be made with no changing field present at the coil.
5.9.1 Automatic Drift Adjustment
The Model 480 can adjust drift by measuring the change in reading over a fixed time interval and
calculating the appropriate coarse drift compensation DAC value. The sequence takes approximately
25 seconds. A well calculated coarse DAC value will give acceptable drift performance for most
applications. The fine drift compensation DAC is set to 0 during the operation. The fine DAC can be
set manually or by the DriftTrak algorithm for improved drift performance. An error message will
appear on the instrument display if automatic drift adjustment failed. If the message appears, check
all coil connections, allow the instrument more time to warm up, and try again.
After the coil is connected and the instrument has warmed up, initiate automatic drift adjustment by
pressing the
Drift Adjust key. The message
Begin Auto Adjust
will appear. Press the Enter key
to start or the Escape key to return to the main display. If you pressed the Enter key, you will see the
following display.
­­*ADJUSTING­DRIFT*
­­­For­25­Seconds
The message will remain visible for 25 seconds, then return to the normal display. Pressing the
Escape key during this time will cancel the sequence and return to normal operation.