5B39
GENERAL DESCRIPTION
track-and-hold input circuit. Selected by a high Write Enable
The 5B39 is a single-channel signal conditioning module that
converts a high-level analog input voltage into a floating,
isolated proportional output current of 4 to 20 mA or 0 to 20
mA across loads from 0Ω to 750Ω. The module provides high
accuracy of +0.05%, low nonlinearity of +0.02%, and the
protection of 1500V rms isolation between output-to-input and
output-to power supply. The input common must be held to
within +1V of power common.
input, the hold mode exhibits an output droop rate of 80 uA/s.
This corresponds to a refresh interval of 25 ms for 0.01% span
droop. On power-up, the module’s output remains at 0 mA for
about 100 ms to allow the user to initialize the track-and-hold
circuit.
In applications using one DAC per channel, where the track-
and-hold feature of the 5B39 is not used, the Write Enable input
should be set to low by grounding it to power common, as on
the 5B01 and 5B08 backplanes. The module current output will
then track its input signal.
Signal isolation by transformer coupling uses a proprietary
modulation technique for linear, stable and reliable
performance. A demodulator on the output side of the signal
transformer recovers the original signal, which is then filtered
and converted to an accurate current output by a current (V-to-
I) converter output stage. Output protection enables the 5B39 to
withstand accidental connection to 240V rms power lines
without damage, while isolating computer-side circuitry. In
addition, the 5B39 is mix-and-match and hot-swappable with
all 5B Series modules, so can be inserted or removed from any
socket in the same backplane without disrupting system power.
Generating A Voltage Output Signal – The 0 to 20 mA output
of the 5B39-04 and the 5B39-03, can produce a 0 to +10V
output by connecting a 500Ω conversion resistor across the
modules’ output terminals,. This approach should be used with
caution because the output lacks the low impedance of a true
voltage source. This means that the tolerance and size of the
load impedance relative to the conversion resistor can introduce
significant error. For example, a load impedance < 500kΩ would
contribute <0.1% error.
Track-and-Hold for DAC Applications – In applications where
a single system digital-to-analog converter (DAC) is used to
drive a number of current output channels, the 5B39 includes a
.
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Figure 2
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