IBM 7220 Instruction Manual page 43

the front panel BNC connector marked "B/I", and uses a low-noise (LN) current
to voltage converter.
Input
This control has four settings:-
Flt/DC
The shells of the "A" and "B/I" connectors are connected to chassis ground via a
1 kΩ resistor and the signal channel input is DC coupled.
Flt/AC
The shells of the "A" and "B/I" connectors are connected to chassis ground via a
1 kΩ resistor and the signal channel input is AC coupled. Note that DC coupling
should be used at frequencies of < 1 Hz.
Gnd/DC
The shells of the "A" and "B/I" connectors are connected to chassis ground and
the signal channel input is DC coupled.
Gnd/AC
The shells of the "A" and "B/I" connectors are connected to chassis ground and
the signal channel input is AC coupled. Note that DC coupling should be used at
frequencies of < 1 Hz.
Device
This control allows the selection of the input device when operating in voltage input
mode and has two settings:-
FET
Uses a FET as the input device, for which case the input impedance is 10 MΩ.
This is the usual setting.
Bipolar
Uses a bipolar device in the input stage, for the lowest possible voltage input
noise. In this case the input impedance is 10 kΩ. Note that this selection is not
possible when using the DC coupled input modes.
Chapter 5, FRONT PANEL OPERATION
5-3