Keithley SourceMeter 2400, User Manual

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2400 Series SourceMeter
®
User’s Manual Pulse Mode Operation (Model 2430 only) 5-5
Pulse width delay
When the pulse width setting is greater than the sum of the signal measurement and over-
head times, a delay is used to achieve the desired pulse width. The pulse width delay can
be calculated as follows:
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 measurement time is
167µsec. For the 80µsec overhead time, the pulse width delay is 753µsec:
Pulse Width Delay = 1msec - 167µsec - 80µsec = 753µsec
NOTE
If the result of the pulse width delay calculation is a negative number, pulse
width delay is set to 0sec. A negative number indicates that the pulse width set-
ting is too short (not achievable).
If the result of the pulse width delay calculation is a negative number, the mini-
mum delay that can be set is 60µsec. For example, if the result of the delay cal-
culation is 33µsec, the delay will be set to 60µsec. Resolution for setting pulse
width delay is 10µsec.
Output off-time
Reference and zero measurements
As previously explained in “ Pulse width ,” “ Signal measurement ,” the reference and zero
measurements for a pulse reading are performed during the output off-time of the pulse
period (
Figure 5-2 ). The time to perform these two measurements depends on the speed
setting (NPLC) of the SourceMeter and the power line frequency:
Meas Ref & Zero = 2 x NPLC / Line Frequency
Where: Meas Ref & Zero is the time it takes to measure the reference and zero.
NPLC is the present speed setting (0.01 to 0.1 PLC).
Line Frequency is the frequency of the power line (50 or 60 Hz).
Overhead time
As shown in Figure 5-2 , there is some overhead time that is inherent to the source-measure
process. The 2.9msec is the minimum overhead time that can be achieved during the out-
put off-time. If the SourceMeter is configured to perform additional operations (e.g., math
calculations, relative, store, sweep), this time will be higher.
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