Keithley 2520, User Manual, Page: 68 / 329

3-8 Basic Operation Model 2520 User’s Manual
Detector measurement polarity
Figure 3-4 shows the basic configuration for detector current measurement polarity. With
connections shown in Figure 3-4 A, current will flow into the current input (center conduc-
tor of the triax connector). Under these conditions, the measured current is negative, and
the polarity setting must also be NEGATIVE. Conversely, if the current is flowing out of
the triax connector (
Figure 3-4 B), the measured current is positive, and the polarity setting
must be POSITIVE.
NOTE
Detector current measurements are essentially unipolar, and the polarity setting
must agree with the polarity connections of the photodiode. If the polarity is set
incorrectly, an overflow reading will be displayed.
Voltage bias polarity
The voltage bias outputs are bipolar, and there is no separate polarity setting. Simply set
the voltage bias value to the desired value in the range of ±20V. This bias voltage value
will be output on the inner shield of the detector triax jack relative to the center conductor
terminal. For example, if you set the bias voltage to +10V, the inner shield will be at a
potential of +10V relative to the center conductor of the triax jack.
Figure 3-4
Detector current measurement polarity
Detector 1
or Detector 2
Current Input
Voltage Bias
Output
I
Photodiode
Detector 1
or Detector 2
Current Input
Voltage Bias
Output
I
Photodiode
A. NEGATIVE polarity connections B. POSITIVE polarity connections
Note: Incorrect polarity setting will
result in overflow current reading