7B34

Rev. 0 | Page 2 of 8

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

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.

Figure 2