7B27

Rev. 0 | Page 2 of 8

GENERAL DESCRIPTION

The 7B27 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 an isolated (up to

100 V rms) and protected precision output of either +1 V to +5

V or 0 V to +10V, linear with input voltage. High accuracy

internal cold junction compensation and a predictable upscale

open circuit indication provide a complete signal conditioning

solution. The 7B27 is mix-and-match and hot-swappable with

other 7B Series input modules, so can be inserted or removed

from any socket in the same backplane without disturbing

power. Model 7B27 is rated to operate with a nominal +24 VDC

supply.

The three input pins of Model 7B27 are protected up to +30

VDC. 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 (100 V rms, continuous). Isolated front-

end circuitry power is supplied by a DC/DC converter. The

output section contains a demodulator, 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