Specifications

9
Use Your Power Supply to Measure Pulsed
Current
To adequately specify the power
source for products that exhibit
pulsed and dynamic current loading
(such as digital cellular phones and
hard drives), you need to evaluate
both the peak and dc averages cur-
rent draws.
You could use an oscilloscope to mon-
itor a shunt or a current probe, but
this approach raises issues with volt-
age drops, ground loops, common
mode noise, space, and calibration.
As a simpler and cheaper alternative,
use a power supply with built-in mea-
surement capabilities. The Agilent
66312A and 66332A dynamic measure-
ment dc sources store up to 4,096
data points at sample intervals from
15.6 ms to 31,200 s. Like an oscillo-
scope, they acquire pre- and post-
trigger buffer data by crossing a
user-set threshold. These dynamic
measurement capabilities are illus-
trated in an Agilent VEE program
output panel (Figure 1).
In Figure 2, note the SCPI commands
in the “Set Up Source,” “Measure,”
and “Enter Array” blocks. (You can
use these commands in other pro-
gramming environments as well.)
Note that “MEAS” can be used in
place of “FETC” to cause an immedi-
ate trigger. Obtain subsequent mea-
surement parameters from the same
data by using “FETC.”
Figure 2. Block flow diagram of the Agilent VEE program, showing program details
Tip
8
Figure 1. An Agilent VEE program that makes para-
metric measurements and captures the pulse current
loading of a digital cellular phone