3B47 Datasheet, PDF (2/8 Pages) Analog Devices – Isolated, Linearized, Thermocouple Input

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-
.
3B47
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
of +0.5^oC over the +5^oC to +45^oC ambient temperature range.
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
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