5B42
GENERAL DESCRIPTION
conditioners specified errors. In contrast, the 5B42 is calibrated
and specified with its internal 25Ω sense resistor. Further, the
5B42 signal input, loop supply and the sense resistor are all
protected against accidental application of excess voltages up to
240V rms. Finally, there is no need to install an external sense
resistor on the backplane, but if one is installed it will not affect
5B42 performance.
The 5B42 is a single-channel signal conditioning module that
interfaces with two-wire transmitters, providing an isolated,
regulated 20V supply voltage. The module filters and amplifies
the 4-to-20 mA process-current input to produce an accurately
scaled, low-noise low-impedance output of +1 to +5 V or +2 to
+10 V.
True Three-Port Isolation – The floating, differential input
circuit on the field side eliminates the need for any input
grounding. Signal and power isolation by transformer coupling
uses a proprietary modulation technique for linear, stable and
reliable performance. A demodulator on the computer side of
the signal transformer recovers the original signal, which is then
filtered and buffered to provide a low-noise, low-impedance
output signal. True three-port isolation (Input-Output-Power)
includes common-mode ratings of 1500 V rms between input
and output and input and power, 250V rms between power and
output – no return path is required between the power and
signal output commons.
Filtering and Protection – The 5B42 contains an optimized
five-pole low-pass filter with a -3 dB bandwidth at 100Hz that
provides a low-overshoot step response and exceptionally low
noise of 200 uV pk-pk in a 100kHz bandwidth. Attenuation
(normal mode rejection) increases at a 90 dB/decade rate
beyond 100 Hz.
The module protects the computer side from damage due to
field-side over-voltage faults. The module withstands 240 V rms
at the input terminals without damage, thereby shielding the
internal computer-side circuitry from field-side over-voltage
conditions. In addition, the 5B42 is mix-and-match and hot-
swappable with all other 5B Series modules, so can be inserted
or removed from any socket in the same backplane without
disrupting system power.
Accurate and Stable Performance – The 5B42 maintains
accuracy over the wide operating temperature range of -40oC to
+85oC through design for low parameter drift. This enables the
module to provide output offset drift of only +5 uV/oC and gain
drift of just +25 ppm/oC
A series output switch eliminates the need for external
multiplexing in many applications. The switch is turned on by
an active-low enable input. If the switch is to be on at all times,
the enable-input should be grounded to power common as it is
on the 5B01 and 5B08 backplanes..
Why an Internal Current Sense Resistor? – The 5B42 offers
significant advantages over signal conditioners that require an
external current sense resistor. First, an external resistor is not
protected from accidental connection to a 240 V rms power
line. Next, the external resistor tolerance must be added to the
.
.
Figure 2
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