Advanced Measurement Technology 273A, User Manual

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Model 273A Potentiostat/Galvanostat User’s Manual
CURRENT MAXIMUM RESOLUTION
RANGE COMPENSATION LIMIT
100 nA 20 M 10 k
1 µA 2 M 1 k
10 µA 200 k 100
100 µA 20 k 10
1 mA 2 k 1
10 mA 200 100 m
100 µA 20 10 m
1 A 2 1 m
Consider how the resolution limit affects the accuracy of the programmed value. For example,
assume a resistance of 1.234 k
is entered on the 100 µA range. On that range the resistance
resolution is 10 , giving an actual programmed resistance of 1230 . In other words, the
programmed resistance differs from that entered (front or rear panels) by 4 .
Let us continue with this example to see how error due to the resolution limit can occur when the
current range changes. If, during the experiment, the current range changes to 1 mA, where the
resistance resolution is 1
, the actual programmed resistance will change to 1234 . The
improved resolution allows the actual programmed value to be identically that originally entered.
Although this change could be a problem in some situations, it will usually be relatively minor.
The real problem occurs when shifting to a more sensitive range. For instance, if, in the
example, the current range were to shift to 10 µA, where the resolution limit is 100
, the actual
programmed resistance will become 1200 because the value can only be represented to the
nearest 100 . In other words, the error will now total 34 . Similarly, a further shift to 1 µA
would give a resistance of 1000 (234 error) and a shift to 100 nA would give a resistance of
1000 (1234 error). Note: Should one later shift to less sensitive ranges, the error will be
successively reduced with each current range step.
Clearly, operators need to be mindful of the resolution limit for the "setup" current range and
should key a resistance appropriate to that limit. Also, if more sensitive ranges are used during
the experiment, users will have to be mindful of the impact the changing resolution will have on
the programmed resistance and of the possible consequences of large resistance errors.
Two procedures for establishing positive feedback compensation are provided. The first
procedure applies when the value of R is known. The second applies when R is not known.
u U
1. R KNOWN:
u
a. Press "SET IR." The current value of assumed R will be displayed.
u
b. Key the value of R to be compensated and press ENTER. The new value will be
u
displayed.
c. Press "POSITIVE FEEDBACK." The associated indicator will light and positive feedback
compensation will be established. Note: This pushbutton is a toggle; to turn the
compensation off, simply press POSITIVE FEEDBACK again.
2. R NOT KNOWN:
u