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Lake Shore Model 480 Fluxmeter User’s Manual
Advanced Operation 5-3
5.3.1 Input Resistance
The analog integrator in the Model 480 will not function without an integrating resistance. The
integrating resistance is the sum of input resistance and coil resistance. The input resistance
parameter tells the Model 480 which input resistance to use inside the instrument. There are three
setting values available: 100 k

, 10 k

for normal measurements, and 0

for special applications.
An input resistance of 100 k

is the default setting and is appropriate for most applications. The
Model 480 achieves its best drift performance with this resistance.
An input resistance of 10 k

is used when more sensitivity is required. The full scale for each range
setting drops by a factor of ten when input resistance changed from 100 k

to 10 k

. The improved
sensitivity may only be useful in the presence of very low drift.
The 0

input is used rarely when the coil resistance is very high and can act alone as the integrating
resistance. In these applications an input resistance inside the instrument would serve only to reduce
sensitivity of the measurement. Care must be taken when using the 0

range. Without a large input
resistance the input is more vulnerable to electrostatic discharge (ESD) and other voltage spikes. A
non-zero coil resistance
must be entered for the Model 480 to calculate a display value at all.
Because of the potential for problems, the 0

setting can only be entered with a press and hold
operation and if the coil resistance is zero, the display value will blink.
To select an input resistance press the Coil Setup key. You will see the following display.
Select With­°®
Input R:100k¦
Use the
s
or
t
keys to select between 100 k

and 10 k

. Press the Enter key to accept the change
or the Escape key to cancel the entry and return the previous value. The next screen in the coil setup
will appear. That parameter can be entered if needed, or press the Enter key to continue past it, or
press the Escape key to return to the normal display.
To select an input resistance of 0

press and hold the Coil Setup key for 5 seconds.
Select­With­°®
0¦ Input: No
The 0

setting screen will appear. Use the  or  keys to select Yes or No. Press the Enter key to
accept the change or the Escape key to cancel the entry and return the previous value. The next
screen in the coil setup function will appear. That parameter can be entered if needed, or press the
Enter key to continue past it, or press the Escape key to return to the normal display.