XT2640 Operating Manual
13 July 2016
Page 73 of 187
The button in the OFFSET column allows you to set the signal level which will correspond to the centerline of the chart.
This only affects how the trace will subsequently be displayed and so can be changed afterwards. For this type of
measurement this is typically set to zero.
4.
Press the SINGLE button to initiate an inrush capture. The XT2640 will now wait until an inrush event is detected by the current
exceeding the trigger level set above, as shown by the SINGLE button label changing to WAITING.
5.
Apply power to the device.
6.
The XT2640 screen will detect the current inrush and capture the signals as shown on the screen.
The screen will have a cursor which is automatically set to the position of the maximum inrush current, and the numerical
data to the left of the chart will show the signals at the cursor position so the trace 1 data shows the maximum inrush
current.
You may re‐scale the traces vertically to properly show them on the screen if you wish. This is best accomplished by
pressing the AUTOSCALE button which will automatically adjust the display scaling so that the traces optimally fit on the
chart.
You may zoom in to show more detail horizontally surrounding the inrush event by pressing the ZOOM button and
selecting a zoom timebase which is faster that the timebase used for the capture.
You may move the cursor by dragging it across chart. Pressing the CURSOR button repositions the cursor at the maximum
inrush event position.
7.
The above may be repeated as many times as you wish without requiring any action by you other than pressing the SINGLE
button and then re‐applying power to the device.
8.
Any other screen may be viewed after the inrush capture is completed, the MEAS CONFIG settings were re‐activated and so all
power measurements are as they are configured. This screen is still available though and can be returned to later.
14.2
OBTAINING
A
NUMERICAL
INRUSH
CURRENT
MEASUREMENT
Before performing the inrush measurement in this manner, you must ensure that the present MEAS CONFIG screen settings are
compatible with performing such a measurement, and then replace the ‘normal’ power measurement configuration settings
afterwards.
The XT2640 must be configured typically with a UNFILTERED setting for BANDWIDTH, or alternatively with a specific
frequency bandwidth limit.
All D current option channels which will be used for this inrush current measurement should be configured for the HI A
RANGE selection.
Having checked that the XT2640 is correctly configured, you should now prepare to make the inrush measurement. The example
screen below shows the XT2640 POWER DATA screen which will be used for this purpose.
1.
Turn off the device being tested. It does not matter if the voltage is switched off between the XT2640 and the device (so the
voltage is always present at the XT2640) or at the supply to the device (so the voltage is not initially present at the
XT2640). Typically a device should have power removed for some period of time before re‐applying power for an inrush
measurement (often several minutes).
2.
Select the POWER DATA screen on the XT2640 and configure it to show the desired channel or VPA (the left button across the
top of the screen) and select to show the INRUSH data (the middle button across the top of the screen). The screen will look
similar to that shown in the example above.
3.
Press the CLEAR button on this screen. This will clear any previously made inrush measurements and the screen will show the
highest measurements with the device being tested unpowered (so should be very small current and power). If an inrush
measurement is being repeatedly made to ensure that the worst case measurement is made then you can skip clearing the
previous results, in that case the results shown will only be updated if an inrush measurement exceeds those previously made.
4.
Apply power to the device.
a.
The XT2640 screen will be updated to show the highest data recorded since it was last cleared.
b.
The Apk and A data are the most important results shown for this type of testing, showing the highest peak current
and highest single measurement period RMS current respectively. These provide you with the measurement of the
