7B47

Rev. 0 | Page 2 of 8

GENERAL DESCRIPTION

The 7B47 is a single-channel signal conditioning module that

interfaces, amplifies and filters input voltages from a J, K, T, E, R,

S, B, or N-type thermocouple and provides an isolated and

protected precision output of either +1V to +5V or 0 to +10 V,

linear with input 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 rms of galvanic transformer-based

isolation with a common mode rejection (CMR) of 160 of 160

dB @ 50/60 Hz and a normal mode rejection (NMR) of 60 dB @

50/60 Hz are provided. Rated to operate with a nominal +24

VDC supply, Model 7B47 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 7B47 are fully protected up to

120 V rms line voltages. A one-pole 3 Hz filter preconditions the

thermocouple signal prior to amplification, provided by a low

drift input amplifier. Cold junction compensation (CJC) is

implemented using a thermistor temperature sensor embedded

under the input screw terminal block on a 7B Series backplane.

A voltage reference source acts to offset the thermocouple

signal in accordance with the specified lower bound on the

input temperature range. A current source provides the upscale

open circuit indication. 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 demodulator,

linearizer. 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 down to 2

kΩ .

Figure 2