Preamp Out - Keithley 6517A User Manual

Front Panel Operation

2.10.2 Preamp out

The PREAMP OUT of the Model 6517A follows the signal
amplitude applied to the INPUT terminal. Some possible
uses for the inverting PREAMP OUT include buffering of
the input signal, as well as for guarding in the volts mode.
Connections and equivalent circuits for the preamp output
are shown in Figure 2-41. Full-range outputs for various
functions and ranges are listed in Table 2-17. Since the
PREAMP OUT signal is not corrected during calibration,
gain error of up to 15% may appear at this output, depending
on function and range selection. For all volts range,
PREAMP OUTPUT accuracy is typically 10ppm.
WARNING
High voltage may be present between
the PREAMP OUT and COMMON ter-
minals depending on the input signal
(see Table 2-17).
CAUTION
Connecting PREAMP OUT, COM-
MON, or 2V ANALOG OUTPUT to
earth while floating input may damage
the instrument.
2-52
Note that the PREAMP OUT output resistance is 1Ω. The
output resistance appears between Input Low and Analog
Output Low to keep the resistor out of the loop when using
external feedback elements. To keep loading errors under
0.1%, the device connected to the PREAMP OUT should
have a minimum input impedance of 100kΩ.
CAUTION
To prevent damage to the Model 6517A,
do not connect a device to PREAMP
OUT that will draw more than ±100µA.
For example, at 200V, the impedance
connected to PREAMP OUT must be at
least 2MΩ (200V/100µA = 2MΩ).
Table 2-17
Full-range PREAMP OUT values
Function* Range
Volts 2V
20V
200V
Amps 2nA, 2µA, 2mA
20pA, 20nA, 20µA, 20mA
200pA, 200nA, 200µA
Coulombs 2nC, 20nC, 200nC
2µC
*PREAMP OUT value for the Ohms function corresponds to the
value for the Amps range that is being used to make the measurement.
Full-range
value
2V
20V
200V
2V
20V
200V
20V
200V