Technical data

110
Applications Information 10 Most frequently asked questions about using
dc power products
(Continued)
Power Products Catalog 2002-2003 For more detailed specifications see the product manual at www.agilent.com/find/power
Agilent Technologies
When the CC circuits are used, the
load can be viewed as many resis-
tors, all the same value (the resolu-
tion), in parallel to produce the
desired resistance. Then, changing
the resistance is like changing the
number of discrete resistors in
parallel. Therefore, the resolution is
the value of one of these parallel
resistors, and putting resistors in
parallel changes the conductance
measured in siemens. For the
60501B, the “discrete resistor” or
resolution that can be programmed
is 0.14 mS (=7.14 kohms).
For example, in the 2 kohm range,
you can program the load input from
2 ohms to 2 kohms (0.5 S to 0.5 mS)
with a resolution of 0.14 mS. This
would be the equivalent of starting
with about 3568 7.143 kohm resis-
tors in parallel with each other, and
in parallel with a 2 kohm resistor,
and removing one at a time until you
had only the 2 kohm resistor left.
Note that the resolution of the
conductance is constant at 0.14 mS,
however, the resolution of the total
parallel resistance is not constant.
It depends on how many resistors
you have in parallel.
If you have two 7.143 kohm resis-
tors in parallel and remove one, the
resolution looks like 3571.5 ohms. If
you have 3568 7.143 kohm resistors
in parallel and remove one, the
resolution looks like (7143/3567) -
(7143/3568) = 0.561 mohms. But the
conductance resolution is constant
at 0.14 mS.
10
Can Agilent power supplies be
programmed from 0 to full output
voltage using a 0 to 10 V signal
source?
Yes, many Agilent power supplies
feature remote voltage programming
or analog programming capability.
However, there is a potential danger
in analog programming any power
supply, especially a high voltage
supply. If the 0 to 10 V programming
source is a typical, non-isolated,
low-cost, digital-to-analog converter
(DAC), it is probably grounded
through its digital inputs and/or
through the computer’s internal
power supplies, which are grounded
through the computer’s power cord.
It’s easy to overlook this, and the
mistake can be very expensive.
If the DAC is non-isolated (or iso-
lated only up to 42 V above ground)
and one of the output terminals of
the power supply is grounded, either
directly or through the UUT, the out-
put capacitor of the power supply
can discharge through the computer
backplane, motherboard, and the I/O
common through the computer
power cord ground. The resulting
high current may even last long
enough to vaporize the thin ground
tracks on some or all of the printed
circuit boards in the PC.
Be sure the programming source is
electrically isolated, is operated from
isolated power supplies, and is rated
for floating voltages up to the full
output voltage of the programmed
supply. This is necessary so no
one is hurt, and no equipment is
damaged, no matter which output
terminal of the power supply or
UUT is grounded.
For additional questions and
answers visit our web site
at www.agilent.com/find/answers