7B33 Isolated, Voltage or Current Input

The 7B33 is a single-channel signal conditioning module that interfaces, amplifies and filters unipolar voltage inputs and provides a protected precision output of either +1 V to +5 V or 0 V to +10 V. To measure a process current input, a plug-on 250 Ω current sensing resistor, Model AC1391, may be installed directly on the 7B backplane, using available pin sockets. The external current sense resistor allows the current loop to be maintained even when the module is removed from the backplane. Model 7B33 features a nonlinearity of ±0.02% maximum and an accuracy of ±0.1% maximum (±0.01% typical). 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 105 dB @ 50/60 Hz is provided. Rated to operate with a nominal +24 V DC supply, Model 7B33 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 7B33 Series Module

The two input pins of Model 7B33 are fully protected up to 120 V rms line voltage. A one-pole 100 Hz filter preconditions the input signal prior to amplification 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 @100 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 of 2 kΩ minimum.