3B37_15 Datasheet, PDF (2/8 Pages) Analog Devices – Isolated, Thermocouple Input

GENERAL DESCRIPTION
The 3B37 is a single-channel signal conditioning module that
interfaces, amplifies and filters input voltages from a J, K, T, E, R,
S or B-type thermocouple and provides isolated simultaneous
voltage and current outputs linear with input voltage. 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. The current output
withstands 130 V rms without damage and interfaces user
equipment through screw terminals located on the 3B Series
backplane. This plug-in, mix-and-match, hot-swappable module
is easily field calibrated via front-panel zero and span
adjustments for both voltage and current outputs.
Accurate and System Ready – 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 47MΩ, 0.25
Watt resistor across screw terminals 2 and 4 on the 3B Series
backplane
3B Series Custom Ranging Program – Externally-
programmable version Model 3B37-X-00, enable the user to
configure a special input range by using the optional plug-on
.
3B37
AC1310 ranging card, which houses user-supplied resistors to
determine zero and span. To facilitate selecting resistors, a
Windows program, 3B-Custom, calculates resistor values based
on the user-desired input/output ranges.
Inside the 3B37 Module – 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) or can be externally
programmed (Model 3B37-X-00) via user-supplied resistors
inserted in the optional AC1310 plug-on ranging card. Zero
suppression can exceed 100% of the input range. This enables
suppression of a zero-scale input value amny times larger that
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
users a proprietary modulation technique for linear, stable and
reliable performance. A demodulator on the computer side of
the signal transformer recovers the original signa, which is then
filtered and buffered to provide a low-noise, low-impedance
output voltage, this output also drives a voltage-to-current (V/I)
converter to provide a simultaneous current output for
interfacing versatility.
.
Figure 2
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