IBM 7220 Instruction Manual page 134

Appendix E, ALPHABETICAL LISTING OF COMMANDS
LF [n]
LINE50 [n]
LOCK
LR[.]
E-10
Signal channel line frequency rejection filter control
In instruments manufactured prior to June 1996, the value of n sets the mode of the
line frequency notch filter according to the following table:
n Selection
0 Off
1 On (i.e. reject 50/60 Hz and 100/120 Hz)
In instruments manufactured after June 1996, the value of n sets the mode of the line
frequency notch filter according to the following table:
n Selection
0 Off
1 Enable 50 or 60 Hz notch filter
2 Enable 100 or 120 Hz notch filter
3 Enable both filters
Users may identify which version of the instrument they have by sending the
command LF 3; if this is accepted by the instrument, it was made after June 1996,
but if it generates a command error, it was made prior to this date.
Units made after June 1996 respond in addition to the command, LINE50, which sets
the notch filter centre frequency.
Signal channel line frequency rejection filter centre frequency control
The value of n sets the line frequency notch filter centre frequency according to the
following table:
n Notch filter mode
0 60 Hz (and/or 120 Hz)
1 50 Hz (and/or 100 Hz)
Units made prior to June 1996 generate an Invalid Command (bit 1 of the serial poll
status byte is asserted) to the LINE50 command.
System lock control
Updates all frequency dependent gain and phase correction parameters.
Log ratio output
In integer mode, the LR command reports a number equivalent to
1000 log (X / ADC1) where X is the value that would be returned by the X command
and ADC1 is the value that would be returned by the ADC1 command. The response
range is - 3000 to +2079.
In floating point mode, the LR. command reports a number equivalent to
log (X / ADC 1). The response range is -3.000 to +2.079.