3.5.3 Modules with two current measurement ranges
High Precision HV modules with two current ranges are a particular case. In these HV modules the high current output is
combined with a picoampere resolution in the low current measurement range. The range switching is done by the
microprocessor depending on I
meas
:
High measuring range:
I
nom-low
< I
meas
< I
nom
Low measuring range:
0
< I
meas
< I
nom-low
The typical value for I
nom-low
is 20 μA.
As long as a set current in the high measuring range is used, everything is working as described above. If a set current in low
measuring range is specified, the current limitation is set to 120 % of the low measuring range.
Example: I
nom-low
= 20 μA
➜
current limitation is set to 24 µA if I
set
= 10 µA
Now the channel operates in the low measuring range only. A software comparison of set current I
set
and measured current I
meas
is performed in addition to the described hardware CC and CV signals sampling.
With this principle, two requirements are met:
•
the output current will not exceed 24 microamps even during fast changes and
•
the delayed trip function is extended into the region of very small currents (picoampere) for these HV modules.
For the software comparison, a delay between 80 milliseconds and 1 second must be expected. This depends on the modules
ADC (Analog-to-digital-converter) configuration.
This time can be adjusted by changing the ADC sample rate to meet the requirements of the application. Higher ADC sample
rates lead to shorter delays but also reduce the resolution.
If the
Delayed Trip
function is activated the voltage ramp should be limited to 1 % of V
nom
before. Higher values could trigger a trip
by internal charge balancing during a ramp, even though the output current does not exceed the set value I
set
.
If the connected load contains capacities or if I
set
is very small, it might be necessary to further reduce the ramp speed.
Alternatively, the
Delayed Trip
can be activated only after the completion of the ramp.
INFORMATION
INFORMATION
An activated KillEnable feature disables the Delayed Trip function.
An active
KillEnable
function disables the
Delayed Trip
function. If
KillEnable
is active and a trip occurs, the channel is shut down
without ramp at the fastest hardware response time (smaller than 1 ms). However, the actual discharge time strongly depends
on the connected load.
EHS High Voltage Power Supply series | Last changed on: 2022-03-14 |
www.iseg-hv.com
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