3.7 Floating GND configuration
The NHR module is a module with Common Floating Ground (CFG). All HV-channels have a common return potential
(module GND), which is galvanically isolated from the crate GND. A protection circuit prevents differences between the
two GND potentials of more than 56V. The galvanic isolation can be removed by placing a jumper on a two-pin connector
located in a ventilation slot on the top of the module (see
The GND of the digital interfaces (USB and CAN) is isolated from both, the module GND and the crate GND.
3.8 Current limitation
3.8.1. Constant Current Mode
The Constant Current Mode (CC) is the default response on an increased output current. If the output current would
exceed the set current (I
set
) at the specified set voltage (V
set
) the channel operates as a constant current source at I
set
. For
modules with one current measurement range the module can operate in CC Mode for I
set
values in the range
I
nom
≥ I
set
≥ 5E-04 • I
nom
. Although the modules accepts smaller values I
set
, the CC Mode can only operate down to the given
limitation. Smaller set value will only affect the funcions
KillEnable
and
Delayed trip
, described below.
Modules with two current measurement ranges can operate in CC Mode with I
set
values down to 200 nA. The following
limitations must be considered when operating a channel with I
set
values in the lower current measurement range (i.e.
typically <20µA):
•
If I
set
< 20µA the maximum voltage ramp speed is limited to 1 % of V
nom
. If the load has a significant capacitance it might
be necessary to further reduce the voltage ramp speed to avoid ramp instabilities.
•
While a channel is operating in CC Mode it is not possible to switch between the two current measurement ranges, i.e.
the set current cannot be changed from a value > 20 µA to a value < 20 µA or vice versa. To change the set current
across the measurement range boundary the channel must stop operation in CC mode (i.e. by switching off the channel
or reducing the voltage such, that it operates in Constant Voltage Mode (CV)).
3.8.2. KillEnable
The function
KillEnable
forces the shut down of a channel at the fastest hardware response time (smaller than 1 ms) if a
specified trip current is exceeded. If
KillEnable
is active the value of the set current (I
set
) defines the trip current. An
approach or exceedance of this current (detected by a hardware signal) will immediately shut off the channel without
ramp. However, the actual discharge time strongly depends on the connected load.
The following limitations must be considered if the function
KillEnable
is activated:
•
Maximum voltage ramp speed is limited to 1 % of V
nom
. To avoid unintended current trips during ramps it might be
necessary to further reduce the ramp speed for very small trip currents or capacitive loads. Alternatively
KillEnable
can
be activated only after the completion of the ramp.
•
The minimum trip currents for a hardware detection is 5E-04 • I
nom
for modules with one current measurement range
and 200 nA for modules with two current measurement ranges. It is possible to specify smaller trip values, however
there is no hardware current limitation below the hardware detection limits. Also, the response time on a trip that does
not triggers the hardware detection can be up to 1s.
•
Modules with two current measurement ranges do not change the current measurement range if
KillEnable
is active.
The channel remains in the high measurement range if I
set
> 20µA and in the low measurement range for I
set
≤ 20µA. It is
not possible to switch the current measurement while a channel is switched on and
KillEnable
is active, i.e. the set
current cannot be changed from a value > 20 µA to a value < 20 µA or vice versa. If it is intended to switch the current
measurement range, the channel must be switched off or
KillEnable
must be deactivated for altering the current set
value.
NHR – NIM standard High Voltage Power Supply | Last changed on: 25.11.2019 |
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