3b34-03 Analog Devices, Inc., 3b34-03 Datasheet - Page 2

• Manufacturer Part Number: 3b34-03
• Description: Isolated, Linearized Rtd Input
• Manufacturer: Analog Devices, Inc.

GENERAL DESCRIPTION
The 3B34 is a single-channel signal conditioning module which
amplifies, protects, filters, linearizes, and isolates analog input
voltages from a wide variety of two-, three-, and four-wire
Resistor Temperature Detectors (RTDs), providing
simultaneous precision voltage and current outputs, linear to
input temperature. RTD excitation current and three-wire lead
resistance compensation provide a complete signal conditioning
solution. The 3B34 protects its computer side outputs from
damage and loss of signal integrity by isolating them up to
+1500V peak and shielding its input and excitation circuit from
damage from field-side over-voltage faults up to 220V rms. The
current output withstands 130V rms without damage and
interfaces to user equipment through screw terminals on the 3B
Series backplane. The 3B34 is a plug-in, mix-and-match, hot-
swappable module, easily field calibrated via front-panel zero
and span adjustments for both voltage and current outputs.
3B Series Custom-Ranging Program – Externally-
programmable Model 3B34-00, enables the user to configure a
special input range by using the optional plug-on 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.
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Figure 2
A differential chopper-stabilized low-drift input amplifier
provides stable gain and long-term stability. This enables the use
of very low RTD excitation current to minimize self-heating
and preserve measurement accuracy. A 250 uA excitation
current for platinum and nickel RTDs and a 1mA excitation
current for copper RTDs is provided to create an input voltage
to the 3B34. For three-wire RTDs, the excitation current flows
through the third RTD lead to eliminate the effect of lead
resistance with an accuracy of +0.02oC/W. Internal multi-pole
low-pass filtering with a 3-Hz cutoff (-3dB) enhances normal-
mode and common-mode ejection at 50/60 Hz, enabling
accurate measurement of small signals in high electrical noise.
The differential input circuit on the field side is fully floating,
eliminating the need for any input grounding. Signal isolation is
accomplished by transformer coupling using 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; this output also drives a voltage-to-current converter to
provide a simultaneous current output for interfacing versatility.
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3B34