Keithley 2002, Руководство пользователя

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Front Panel Operation
2-40
2.5 Range
The selected measurement range affects both the ultimate
resolution and accuracy of the measurements as well as the
maximum signal that can be measured. The range setting
(fixed or auto) for each measurement function is saved when
changing functions.
2.5.1 Display resolution
The display resolution of a Model 2002 reading depends on
the selected range and the resolution setting. The default and
maximum display resolutions for every range on each func-
tion are included in the specifications of Appendix A.
You can set the display resolution, as described in paragraph
2.4.
2.5.2 Maximum readings
The full scale readings for every range on each function are
included in the specifications of Appendix A. Input values
more than the maximum reading listed cause the “Overflow”
message to be displayed.
2.5.3 Manual ranging
To select a manual range, simply press the RANGE
▲
or
▼
key. The instrument changes one range per key press. The
selected range is displayed on the bottom line of the display.
If the instrument displays the “Overflow” message on a par-
ticular range, select a higher range until an on-range reading
is displayed. Use the lowest range possible without causing
an overflow to ensure best accuracy and resolution.
Note that the frequency and temperature functions have just
one range. For the frequency functions, the RANGE
▲
and
▼
keys increase and decrease the trigger level by 0.5%. On
temperature the keys have no effect.
2.5.4 Autoranging
To enable autoranging, press the AUTO key. The AUTO
annunciator turns on when autoranging is selected. While
autoranging is selected, the instrument automatically
chooses the best range to measure the applied signal.
NOTE
Autoranging should not be used when op-
timum speed is required.
Note that up-ranging occurs at 105% of range, while down-
ranging occurs at 10% of range.
To cancel autoranging, press AUTO or the RANGE
▲
or
▼
key. Pressing AUTO to cancel autoranging leaves the instru-
ment on the present range.
Pressing the RANGE
▼
key when the instrument has auto-
ranged to the lowest range displays the following momentary
typical message and leaves the instrument in autorange:
Range at minimum: 200 mVDC
The instrument operates similarly if the RANGE
▲
key is
pressed when the instrument has autoranged to the highest
range.
For the frequency function, pressing the AUTO key returns
the trigger level to 0.0V. The AUTO key has no effect in the
temperature function.
2.6 Relative
The rel (relative) operation subtracts a reference value from
actual readings. When rel is enabled by the REL key, the in-
strument uses the present reading as a relative value. Subse-
quent readings will be the difference between the actual
input value and the rel value. You can also enter and enable a
relative value from the CONFIG-REL display (see para-
graph 2.6.1).
A rel value can be established for each measurement func-
tion. The state and value of rel for each measurement func-
tion are saved when changing functions.
Once a rel value is established for a measurement function,
the value is the same for all ranges. For example, if 150V is
set as a rel value on the 200V range, the rel is also 150V on
the 1000V, 20V, 2V, and 200mV ranges.
A relative value can be as large as the highest range for the
particular function. Table 2-26 lists the allowable range of rel
values for each function.
Selecting a range that cannot accommodate the rel value
does not cause an overflow condition, but it also does not
increase the maximum allowable input for that range. For
example, on the 2mA range, the Model 2002 still overflows
for a 2.1mA input.