Command Descriptions; Signal Channel - IBM 7220 Instruction Manual

Chapter 6, COMPUTER OPERATION

6.4 Command Descriptions

6.4.01 Signal Channel

IMODE [n] Controls whether the instrument input is connected to a current or a voltage
VMODE [n]
FET [n]
FLOAT [n] Input connector shield float / ground control
6-10
This section lists the commands in logical groups, so that, for example, all commands
associated with setting controls affecting the signal channel are shown together.
Appendix E gives the same list of commands but in alphabetical order.
preamplifier
The value of n sets the input mode according to the following table:
n Input mode
0 Current mode off - voltage mode input enabled
1 High bandwidth (HB) current mode enabled - connect signal to B input
connector
2 Low noise (LN) current mode enabled - connect signal to B input connector
If n = 0 then the input configuration is determined by the VMODE command.
If n > 0 then current mode is enabled irrespective of the VMODE setting.
Voltage input configuration
The value of n sets up the input configuration according to the following table:
n Input configuration
0 Both inputs grounded (test mode)
1 A input only
3 A-B differential mode
Note that the IMODE command takes precedence over the VMODE command.
Voltage mode input device control
The value of n selects the input device according to the following table:
n Selection
0 Bipolar device, 10 kΩ input impedance, 2 nV/√Hz voltage noise
1 FET, 10 MΩ input impedance, 5 nV/√Hz voltage noise
The value of n sets the input shield switch according to the following table:
n Selection
0 Ground
1 Float (connected to ground via a 1 kΩ resistor)