Keithley 263 User Manual

OPERATION
Figure 3-3. External Source
When sourcing current to EXT INPUT, maximum burden
voltage of the Model 263 can be calculated as follows:
Maximum Burden V = IQ x I
where
I = Current setting of the external source.
3.3.2 Resistance Source
Resistance sourcing is a simple matter of selecting the ap-
propriate resistor. When the Model 263 is calibrated, the
resistors are accurately measured and the instrument is
adjusted to display those values. Thus, when the instru-
ment is configured to source a resistance, the display will
provide the measured reading of that resistor.
On the lGC2,lOGn and lOOGO ranges, the resistor reading
on the display will change as the instrument warms up,
and as ambient temperature changes occur. These resistors
have a high negative temperature coefficient (TC). As the
temperature of the resistor rises, its resistance decreases.
The display is able to track the output resistance because
a TC profile for each of these three resistors is established
when the instrument was calibrated. In effect, the instru-
ment “knows” what the output resistance is at all operat-
ing temperatures. This temperature compensation feature
can be disabled by front panel Program tc (see paragraph
3.9.3). With temperature compensation disabled, the in-
strument will display the resistor reading that was
measured (during calibration) when the internal tempera-
ture approximated the normal operating temperature. See
paragraph 3.11.1 for more information on temperature
compensation.
3.3.3 Current and Charge Source
The Model 263 provides two methods to source c&rent
for the current and charge functions. When the AMPS or
COUL button is pressed, the active current source is
selected. When SHIFT AMPS or SHIFT COUL is pressed,
the passive (V/R) source is selected.
Active Current Source (AMPS)
Figure 3-4 shows a simplified schematic of the active cur-
rent source (AMPS). With this method, the output cur-
rent remains at the programmed level regardless of the
load resistance, as long as the compliance voltage of f 12V
is not exceeded. Compliance voltage is the maximum
voltage that can appear across the unknown with the pro-
grammed current still being sourced.
3-4

Keithley 263 Specifications

General

Brand	Keithley
Model	263
Category	Test Equipment
Language	English