7B47 Isolated, Linearized Thermocouple Input

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 +1 V to +5 V 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 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 V DC 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.

Inside the 7B47 Series Module

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 @ 3Hz), 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

¹ Accuracy includes the effects of repeatability, hysteresis and conformity. The CJC sensor accuracy should be added to the 7B47 module accuracy listed in these tables in order to compute the overall system accuracy.