6482-901-01 Rev. A / August 2012 Return to Section Topics 9-3
Model 6482 Dual-Channel Picoammeter / Voltage Source Reference Manual Section 9: Measurement Concepts
NOTE See Section 8 for trigger model details.
Delay phase
The delay phase of the source-delay-measure (SDM) cycle allows the source to settle before the
measurement is performed. The delay period depends on how the source delay is configured. The
source delay can be set manually from 0000.0000 s to 9999.9980 s. If using autodelay, the delay
is set automatically; see Section 3 for details.
The manually set delay (up to 9999.998 sec) is available to compensate for longer settling
required by external circuitry. The more capacitance measured at the output, the more settling time
is required for the voltage bias source. The actual delay period needed can be calculated or
determined by experimentation with different values. The slew rate of the output circuit is constant
at about 3.07 ms/V. Therefore, the minimum source delay must be 3.07 ms × voltage step size.
NOTE The delay period is the same for both channels. If you change the delay on one channel,
the delay period on the other channel will change to the same value.
Measurement time
The measure time depends on the selected measurement speed. For example, if speed is set at
0.01 PLC (power line cycles), the measure time would be 167 µsec for 60 Hz operation (0.01/60).
Sweep waveforms
There are three basic sweep types to select from: Linear staircase, logarithmic staircase, and
custom, as shown in Figure 9-3.
Staircase sweeps
The linear staircase sweep goes from the start level to the stop level in equal linear steps. The
logarithmic staircase sweep is similar to the linear staircase sweep, except it is done on a
logarithmic scale with a specified number of steps per decade.
Custom sweep
The custom sweep lets you construct your own sweep by specifying the number of measure points
and the source level at each point. See Section 7 for more details on sweep operation.
SDM cycle during sweeps
A source-delay-measure (SDM) cycle is performed on each step (or point) of the sweep; one
measurement will be performed at each step (level). The time spent at each step (level) depends
on how the SDM cycle is configured (in other words, the source delay and measure speed
configuration) and the trigger delay (if used).
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