User Manual

Page 36
ELR 9000 Series
www.elektroautomatik.de
[e-mail]
EA Elektro-Automatik GmbH
Helmholtzstr. 31-33 • 41747 Viersen
Germany
Fon: +49 2162 / 3785-0
Fax: +49 2162 / 16230
3.2.3 Resistance regulation / constant resistance
Electronic loads whose operating principle is based on a variable internal resistance have resistance regulation
and constant resistance mode (CR) as a matter of course. The load attempts to set the internal resistance to the
user dened value and to adjust the input current dependant on the input voltage according to Ohm’s law I
IN
= U
IN
/ R
SET
. The internal resistance is naturally limited between almost zero (current limiting or power limiting active)
and maximum (resolution of current regulation too inaccurate). As the internal resistance cannot have a value of
zero, the lower limit is dened to the an achievable minimum. This ensures that the electronic load, at very low
input voltages, can consume a high input current from the source, up to the maximum.
With resistance adjustment being active, i.e. mode R/I, the function generator will be ofine.
3.2.4 Power regulation / constant power / power limiting
Power regulation, also known as power limiting or constant power (CP), keeps the
DC input power of the device at the set value, so that the current owing from the
source,together with the source voltage, achieves the set power value. Power limit-
ing then limits the input current according to I
IN
= P
SET
/ U
IN
as long as the voltage
or current source is able to provide this power.
Power limiting operates according to the auto-range principle such that at lower
input voltages higher current ows and vice versa in order to maintain constant
power within the range P
N
(see diagram right)
If the DC input is switched on and constant power operation is active, then the condi-
tion “CP operation active” will be shown on the graphic display by the abbreviation
CP and this message will be passed as a signal to the analog interface, as well
stored as status which can also be read as a status message via digital interface.
Constant power operation impacts the internal set current value. This means that the maximum set current may
not be reachable if the set power value according to I = P / U sets a lower current. The user dened and displayed
set current value is always the upper limit only.