5B35

Rev. 0 | Page 2 of 9

GENERAL DESCRIPTION

The 5B35 is a single-channel signal conditioning module that

amplifies, filters, isolates and protects a wide variety of four-wire

RTDs. The module provides a linearized, highly accurate output

of 0 to +5V.

Accurate and Stable Performance

– The four-wire

configuration of the 5B35 supplies RTD excitation from a

precision, protected current source: two RTD wires carry the

excitation current and two wires serve as signal-input leads that

measure the voltage across the RTD. Because no excitation

current flows through the signal input leads, the length or

resistance of the leads creates little or no RTD measurement

error. A low-drift chopper-stabilized differential amplifier

allows use of very low excitation current to minimize error due

to RTD self heating. The amplifies low input offset drift of

the full operating temperature range.

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 rating of: 1500V 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

– An optimized five-pole Butterworth

filter (with a 4-Hz bandwidth) provides 116dB of normal-mode

rejection (noise on signal) at 60 Hz and 108 dB at 50 Hz. Output

noise is an exceptionally low 0.3 Mv p-p in a 100 kHz

bandwidth and 6 mV p-p in a 5 MHz bandwidth.

The 5B35 protects the computer side from damage due to field-

side over-voltage faults. The module withstands 240V rms at

the input terminals without damage, thereby shielding the

internal computer-side circuitry from field-side over-voltage

conditions. In addition, the 5B35 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.

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.

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Figure 2