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6-24
Chapter 6, COMPUTER OPERATION
and HC commands. It also interacts with the LEN command and affects the values
reported by the M command.
LEN [n] Curve length control
The value of n sets the curve buffer length in effect for data acquisition. The
maximum allowed value depends on the number of curves requested using the CBD
command, and a parameter error results if the value given is too large. For this
reason, if the number of points is to be increased and the number of curves to be
stored is to be reduced using the CBD command, then the CBD command should be
issued first.
NC New curve
Initializes the curve storage memory and status variables. All record of previously
taken curves is removed.
STR [n] Storage interval control
Sets the time interval between successive points being acquired under the TD or TDC
commands. n specifies the time interval in ms with a resolution of 5 ms, input values
being rounded up to a multiple of 5. The longest interval that can be specified is
1000000 s corresponding to one point in about 12 days.
In addition, n may be set to 0, which sets the rate of data storage to the curve buffer
to 800 Hz. However this only allows storage of the X and Y outputs. There is no need
to issue a CBD 3 command to set this up since it happens automatically when
acquisition starts.
If the time constant is set to 5 ms or longer, then the actual time constant applied to
the stored X and Y output values will be 640 µs, but if it is set to a shorter value then
this will be the time constant actually used.
TD Take data
Initiates data acquisition. Acquisition starts at the current position in the curve buffer
and continues at the rate set by the STR command until the buffer is full.
TDC Take data continuously
Initiates data acquisition. Acquisition starts at the current position in the curve buffer
and continues at the rate set by the STR command until halted by an HC command.
The buffer is circular in the sense that when it has been filled, new data overwrites
earlier points.
EVENT [n] Event marker control
During a curve acquisition, if bit 13 in the CBD command has been asserted, the
lock-in amplifier stores the value of the Event variable at each sample point. This can
be used as a marker indicating the point at which an experimental parameter was
changed. The EVENT command is used to set this variable to any value between 0
and 32767.