3B47

Rev. 0 | Page 2 of 8

GENERAL DESCRIPTION

The 3B47 is a single-channel isolated thermocouple signal-

conditioning module which interfaces, amplifies, isolates,

protects, linearizes and filters analog input voltages from a J, K,

T, E, R, S or B-type thermocouple. The thermocouple input

signal is internally linearized to provide an output voltage which

is linear with temperature, High accuracy internal cold junction

compensation and a predictable upscale open circuit indication

provide a complete signal conditioning solution. To accurately

measure low level signals in electrically noisy environments,

+1500 V peak of galvanic transformer-based isolation with a

common mode rejection (CMR) of 160 dB @ 50/60 Hz and a

normal mode rejection (NMR) of 60 dB @ 50/60 Hz are

provided. This plug-in, mix-and-match, hot-swappable module

is easily field calibrated via front-panel zero and span

adjustments.

A chopper-stabilized low-drift input amplifier assures stable

long-term stability. At the amplifier input, a zero-scale input

voltage is subtracted from the input signal to set the zero-scale

value. For user convenience, the zero and span optionally can be

factory configured to meet custom needs (Model 3B37-

CUSTOM). Zero suppression can exceed 100% of the input

range. This enables suppression of a zero-scale input value

many times larger than the total span for precise expanded-

scale measurements of a selection portion of an input signal.

The differential input circuit on the field side is fully floating,

eliminating the need for any input grounding. Signal 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 voltage.

Internal cold-junction compensation largely corrects errors

arising from parasitic thermocouples formed by thermocouple

connection to the input screw terminals, providing an accuracy

The module generates a predictable upscale signal to indicate an

open thermocouple; for a downscale response, connect a 47

MΩ, 0.25 Watt resistor across screw terminals 2 and 4 on the 3B

Series backplane.

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Figure 2