User Manual

2400 Series SourceMeter
®
User’s Manual Pulse Mode Operation (Model 2430 only) 5-5
The maximum pulse width for the 10A range (source or measure) is 2.5msec. If
the setting is >2.5msec, the SourceMeter will limit the pulse width to 2.5msec.
Signal measurement
A pulse reading consists of three measurement conversions. The signal (pulse) is
measured, a precise internal reference is measured, and finally, zero (common) is
measured. The reading is calculated from these measurements.
As shown in Figure 5-2, the signal measurement (Meas Sig) is a component of the
pulse width, while the reference and zero measurements (Meas Ref & Zero) are
components of the off-time. The measurement process is split up this way to allow
the shortest possible pulse width. The time to perform the signal measurement
depends on the speed setting (NPLC) of the SourceMeter and the power line fre-
quency:
Meas Sig = NPLC / Line Frequency
Where: Meas Sig is the time it takes to measure the signal.
NPLC is the present speed setting (0.004 to 0.100 PLC).
Line Frequency is the frequency of the power line (50 or 60 Hz).
NOTE For front panel operation, the menu to set speed is displayed by pressing
the SPEED key. For remote operation, speed is set using an :NPLCycles
command. See
Section 7, “Speed,” for details.
Overhead time
As shown in Figure 5-2, there is some pulse width overhead time that is inherent
to the measurement process. The 80µsec is the minimum overhead times that
can be achieved. If the SourceMeter is configured to perform additional opera-
tions (e.g., math calculations, relative, store, sweep), this time will be higher.
Pulse width delay
When the pulse width setting is greater than the sum of the signal measurement
and overhead times, a delay is used to achieve the desired pulse width. This
delay is automatically calculated by the instrument using the following equation:
Pulse Width Delay = PW - Sig Meas - 80µsec
Where: PW is the pulse width setting
Sig Meas is the signal measurement time
80µsec is the minimum pulse width overhead time
For example, assume the pulse width setting is 1msec, and the signal measure-
ment time is 167µsec. For the 80µsec overhead time, the pulse width delay is
753µsec: