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4.
Record the applied current value and the corresponding differential voltage output for that
channel.
Note
Averaging data in multiples of 0.1 seconds helps remove 50 Hz or 60 Hz
noise.
5.
Repeat the previous step at five or more DC current points from ±8 A on the SLSC-12251
and ±30 A on the SLSC-12252.
6.
Repeat Step 3 and Step 4 for all channels.
7.
Use the data for a least squares fit to determine the gain and offset coefficients.
8.
Read back and save the capabilities section of the Non-Volatile Memory (NVMEM).
9.
Modify the saved data in the following ways:
a.
Update the
NI.FIU.CurrentTransducer.Offset
and
NI.FIU.CurrentTransducer.Gain
property values of each channel for which
the calibration values were measured.
b.
Use the "Get Time/Date in Seconds" VI to generate the timestamp in double format
to write to the
NI.FIU.Calibration.Date
property.
c.
Add the number of seconds of the calibration interval to the timestamp to generate
the value to write to the
NI.FIU.Calibration.ExpirationDate
property.
10. Write the modified data back to the capabilities section of the device's NVMEM. Use the
device's serial number and the password
ni
to write this section.
Driving Inductive Loads
When a channel is providing current to an inductive load and the current is interrupted by
opening the switch, the inductor voltage rapidly increases due to V
inductor
= L di/dt. This
inductive kickback, or flyback voltage, is usually limited by placing a catch diode across the
inductor. If a catch diode is not used, the FET switch will enter Avalanche breakdown.
Avalanche breakdown occurs when the flyback voltage exceeds approximately 120% of its
rated breakdown voltage V
(BR)DSS
.
When using an inductive load with no catch diode, it is possible to generate voltages on the
LOAD terminals in excess of 120 V, even if a non-hazardous voltage level is driving the
inductor.
In addition to the hazard of generating high voltages in a low voltage system, Avalanche
breakdown operation is also limited by the energy dissipation available per switch event.
Note
Refer to the
SLSC-12251 Specifications
and
SLSC-12252 Specifications
for
specific values related to Avalanche breakdown operation.
This energy is lower than the 25 °C specifications rating of the FET because the SLSC chassis
can reach internal temperatures of up to 85 °C. Using this energy rating and the Avalanche test
current I
AV
of 150 A from the FET datasheet, the test inductance used to determine the
Avalanche characteristics can be found using the following equation:
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SLSC-12251 and SLSC-12252 User Manual