IBM 7220, Instruction Manual

Page: 43 / 155

5-3
Chapter 5, FRONT PANEL OPERATION
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 k
Ω
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 k
Ω
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 M
Ω
.
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 k
Ω
. Note that this selection is not
possible when using the DC coupled input modes.