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EPS Stromversorgung GmbH
Alter Postweg 101 • 86159 Augsburg
Germany
Fon: +49 821 / 570451-0
Fax: +49 821 / 570451-25
ELR 9000 Series
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
•
For models which accept dangerous voltages, the included DC terminal cover, or an equivalent,
must always be used
•
Whenever the DC input is being re-configured, the device should be disconnected from the
mains, not only switched off on the DC input! Also switch off or even disconnect the source!
3.2
Operating modes
An electronic load 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.
3.2.1 Voltage regulation / Constant voltage
Constant voltage operation (CV) or voltage regulation is a subordinate operating mode of electronic loads. In nor-
mal operation, a voltage source is connected to electronic load, which represents a certain input voltage for the
load. If the set value for the voltage in constant voltage operation is higher than the actual voltage of the source,
the value cannot be reached. The load will then take no current from the source. If the voltage set value is lower
than the input voltage then the load will attempt to drain enough current from the source to achieve the desired
voltage level. If the resulting current exceeds the maximum possible or adjusted current value or the total power
according to P = U
IN
* I
IN
is reached, the load will automatically switch to constant current or constant power opera-
tion, whatever comes first. Then the adjusted input voltage can no longer be achieved.
While the DC input is switched on and constant voltage mode is active, then the condition “CV mode active” will be
shown on the graphics display by the abbreviation CV, as well it will be passed as a signal to the analog interface
and stored as internal status which can be read via digital interface.
3.2.1.1 Speed of the voltage controller
The internal voltage controller can be switched between “Slow” and “Fast” (see
„3.4.3.1. Menu “General Settings”“).
Factory default value is “Slow”. Which setting to select depends on the actual situation in which the device is going
to be operated, but primarily it depends of the type of voltage source. An active, regulated source such as a switch-
ing mode power supply has its own voltage control circuit which works concurrently to the load’s circuit. Both might
work against each other and lead to oscillation. If this occurs it is recommended to set the controller speed to “Slow”.
In other situations, e.g. operating the function generator and applying various functions to the load’s input voltage
and setting of small time increments, it might be necessary to set the voltage controller to “Fast” in order to achieve
the expected results.
3.2.1.2 Minimum voltage for maximum current
Due to technical reasons, all models in this series have a minimum internal resistance that makes the unit to be
provided with a minimum input voltage (U
MIN
) in order to be able to draw the full current (I
MAX
). This minimum input
voltage varies from model to models and is primarily depending on the minimum internal resistance (R
MIN
). The
technical specifications list U
MIN
for every model. If less voltage than U
MIN
is supplied, the load proportionally draws
less current, even less than adjusted.
3.2.2 Current regulation / constant current / current limitation
Current regulation is also known as current limitation or constant current mode (CC) and is fundamental to the
normal operation of an electronic load. The DC input current is held at a predetermined level by varying the internal
resistance according to Ohm’s law R = U / I such that, based on the input voltage, a constant current flows. Once
the current has reached the adjusted value, the device automatically switches to constant current mode. However,
if the power consumption reaches the adjusted power level, the device will automatically switch to power limitation
and adjust the input current according to I
MAX
= P
SET
/ U
IN
, even if the maximum current set value is higher. The
current set value, as determined by the user, is always and only an upper limit.
While the DC input is switched on and constant current mode is active, the condition “CC mode active” will be
shown on the graphics display by the abbreviation CC, as well it will be passed as a signal to the analog interface
and stored as internal status which can be read via digital interface.
