Keithley 6517B, Справочное руководство

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Model 6517B Electrometer Reference Manual Section 5: Measurement options
6517B-901-01 Rev. C / August 2015 5-17
Non-decade current gains
The Model 6517B electrometer input uses internal decade resistance feedback networks for the
current ranges. In some applications, non-decade current gains may be desirable. As shown in the
figure below, an external feedback resistor, R
FB
, can be used to serve this purpose. Limitations on the
magnitude of the feedback current require that the value of R
FB
be greater than 100 Ω .
Figure 65: Non-decade current gains
Range and resolution
The range and resolution setting (fixed or auto) for each measurement function are saved when
changing functions.
Measurement range
The measurement range affects the accuracy of the measurement as well as the maximum signal
that can be measured. The measurement ranges for each function are listed in the specifications. The
maximum input signal level for voltage, current, and charge measurements is 105 % of the
measurement range. For example, the maximum signal level on the 2 V range is 2.1 V
(2 V

1.05 = 2.1 V). When the integrated (average) input level exceeds the selected range, the
OVERFLOW message is displayed. However, if a stray out of range transient (such as a noise spike)
occurs, the message OUT OF LIMIT is displayed (assuming the integrated signal level is still within
the selected range).
For the ohms function, each measurement range has a lower reading limit that is one decade below
the selected range. For example, the 20 M
Ω range has a lower reading limit of 2 M Ω . Measuring a
device that is less than 2 M Ω causes the UNDERFLOW message to be displayed.
With AUTO range selected, the instrument goes to the most sensitive (optimum) range to make the
measurement. Note that with AUTO range selected for the ohms function, the instrument cannot go to
the 2 T
Ω , 20 T Ω , or 200 T Ω ranges since a hazardous voltage level (400 V) may be selected by the
instrument. You must select these ohms ranges manually.
For the amps, ohms and coulombs function, you can set autorange limits to speed up the autoranging
process. Setting limits eliminates upper and lower ranges from the autorange search. This speeds up
the measurement process. These limits are set from the AUTORANGE option of the appropriate
function configuration menu.