7B27 Isolated, Thermocouple Input

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 +10 V, 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 V DC supply.

Inside the 7B27 Series Module

The three input pins of Model 7B27 are protected up to ±30 V DC. 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 (<1 Ω) signal is available at the output to drive loads down to 2 kΩ.