7B34-04-2 Analog Devices Inc, 7B34-04-2 Datasheet - Page 2

• Manufacturer Part Number: 7B34-04-2
• Manufacturer: Analog Devices Inc

GENERAL DESCRIPTION
The 7B34 is a single-channel signal conditioning module that
interfaces, amplifies and filters input voltages from a wide
variety of two- and three-wire platinum, copper and nickel
Resistor Temperature Detectors (RTDs) and provides a
protected precision output of either +1 V to +5 V or 0 V to +10
V, linear with RTD temperature. Three-wire lead resistance
compensation is provided and 2- or 3-wire RTDs may be used.
RTD excitation current, and a predictable upscale open circuit
indication provide a complete signal conditioning solution.
Model 7B34 features a nonlinearity of +0.05% maximum (Pt
RTDs). To accurately measure low level signals in electrically
noisy environments, 1500 V rms of galvanic transformer-based
isolation with a common mode rejection (CMR) of 160 dB @
50/60 Hz and a normal model rejection (NMR) of 60 dB @
50/60 Hz are provided. Rated to operate with a nominal +24
VDC supply, Model 7B34 is mix-and-match and hot-swappable
with other 7B Series input modules, so it can be inserted or
removed from any socket in the same backplane without
disturbing system power.
The three input pins of Model 7B34 are fully protected up to
120 V rms line voltage. A 250 uA excitation current is provided
to create an input voltage to the 7B34. This current also
provides the upscale open circuit indication. A one-pole 3 Hz
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Figure 2
filter preconditions the RTD signal prior to amplification,
provided by a low drift input amplifier. Amplitude modulation
is used to implement transformer isolation (1500 V rms input-
to-output and power). Isolated front-end circuitry power is
supplied by a DC/DC converter. The output section contains a
two-pole low pass filter (-3 dB @ 3 Hz), a buffer amplifier and a
power oscillator. The two-pole output filter and subsequent
buffer ensures that a low noise, low impedance (<1Ω) signal is
available at the output to drive loads to 2 kΩ minimum.
7B34