Signal Channel Output Filters - IBM 7220 Instruction Manual

Chapter 6, COMPUTER OPERATION
FRQ[.]
LOCK

6.4.03 Signal Channel Output Filters

SLOPE [n] Output low-pass filter slope (roll-off) control
TC [n]
TC.
6-14
Reference frequency meter
If the lock-in amplifier is in the EXT or EXT LOGIC reference source modes, the
FRQ command causes the lock-in amplifier to respond with 0 if the reference channel
is unlocked, or with the reference input frequency if it is locked.
If the lock-in amplifier is in the INT reference source mode, it responds with the
frequency of the internal oscillator.
In fixed point mode the frequency is in mHz.
In floating point mode the frequency is in Hz.
System lock control
Updates all frequency dependent gain and phase correction parameters.
The value of n sets the slope of the output filters according to the following table:
n Slope
0 6 dB/octave
1 12 dB/octave
2 18 dB/octave
3 24 dB/octave
Filter time constant control
The value of n sets the time constant of the output according to the following table:
n time constant
0 10 µs
1 20 µs
2 40 µs
3 80 µs
4 160 µs
5 320 µs
6 640 µs
7 5 ms
8 10 ms
9 20 ms
10 50 ms
11 100 ms
12 200 ms
13 500 ms
14 1 s
15 2 s
16 5 s