User manual

Page 26
PSI 5000 A 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. Operation and application
3.1 Personal safety
• In order to guarantee safety when using the device, it is essential that only persons operate
the device who are fully acquainted and trained in the required safety measures to be taken
when working with dangerous electrical voltages
• WhenevertheloadandDCoutputconnectionarebeingre-congured,thedeviceshouldbe
disconnected from the mains, not only the DC output switched off!
3.2 Operating modes
A power supply is internally controlled by different control or regulation circuits, which shall bring voltage, current
and power to the adjusted values and hold them constant, if possible. These circuits follow typical laws of control
systems engineering, resulting in different operating modes. Every operating mode has its own characteristics
which is explained below in short form.
• No-load operation is not a normal operation mode of a voltage source and should not be used
to measure, verify or calibrate anything
• Duetotechnicalreasons,anadjustablepowerwillworklessefcientandaccuratebelow5%
nominal voltage and current. It is recommended to run the device always at levels of >5%,
ideally at levels >50%.
3.2.1 Voltage regulation / Constant voltage
Voltage regulation is also called constant voltage operation (CV).
The DC output voltage of a power supply is held constant on the adjusted value, unless the output current or the
output power according to P = U
OUT
* I
OUT
reaches the adjusted current or power limit. In both cases the device
willautomaticallychangetoconstantcurrentorconstantpoweroperation,whateveroccursrst.Thentheoutput
voltage can not be held constant anymore and will sink to a value resulting from Ohm’s law.
While the DC output is switched on and constant voltage mode is active, then the condition “CV mode active” will
be indicated on the display by the abbreviation CV and can also be read as a status via digital interface.
3.2.2 Current regulation / constant current / current limiting
Current regulation is also known as current limitation or constant current mode (CC).
The DC output current is held constant by the power supply, once the output current to the load reaches the adjusted
limit.ThenthepowersupplyautomaticallyswitchesThecurrentowingfromthepowersupplyisdeterminedbythe
output voltage and the load’s true resistance. As long as the output current is lower than the adjusted current limit,
the device will be either in constant voltage or constant power mode. If, however, the power consumption reaches
the set maximum power value, the device will switch automatically to power limiting and sets the output current
according to I
MAX
= P
SET
/ U
IN
, even if the maximum current value is higher. The current set value, as determined
by the user, is always an upper limit only.
While the DC output is switched on and constant current mode is active, then the condition “CC mode active” will
be indicated on the display by the abbreviation CC and can also be read as a status via digital interface.
3.2.3 Power regulation / constant power / power limiting
Power regulation, also known as power limiting or constant power (CP), keeps the
DCoutputpowerofapowersupplyconstantifthecurrentowingtotheloadin
relation to the output voltage and the resistance of the load reaches the adjusted
power value according to P = U * I resp. P = U² / R. The power limitation then regu-
lates the output current according to I = sqr(P / R), where R is the load’s resistance.
Power limiting operates according to the auto-range principle such that at lower
outputvoltageshighercurrentowsandviceversainordertomaintainconstant
power within the range P
N
(see diagram to the right)
While the DC output is switched on and constant power mode is active, then the condition “CP mode active” will
be shown on the display by the abbreviation CP and can also be read as a status message via digital interface.