7B39 Isolated, Process Current Output

The 7B39 is a single-channel signal conditioning current output module that interfaces, isolates and filters a 0 V to +10 V or +1 V to +5 V input signal and provides an isolated process current output of 0 mA to 20 mA or 4 mA to 20 mA across loads of 0 Ω to 850 Ω. The output current appears at the 7B Series backplane screw terminal block. Model 7B39 features a nonlinearity of ±0.02% maximum and an accuracy of ±0.1% maximum (±0.01% typical). Providing 1500 V rms of galvanic transformer based isolation, output-to-input and power, the 7B39 offers a common mode rejection (CMR) of 110 dB @ 50/60 Hz to preserve the integrity of low level signals in noisy environments. The 7B39 is mix-and-match and hot-swappable with other 7B Series modules, so it can be inserted or removed from any socket in the same backplane without disturbing system power. Model 7B39 is rated to operate with a nominal +24 V DC supply.

Inside the 7B39 Series Module

The input signal from the user's system is buffered and then used to modulate the amplitude of a square wave carrier. The modulated signal is transmitted across the signal transformer and demodulated to retrieve the original input voltage signal. This voltage is then filtered by a two-pole low pass 100 Hz filter, buffered and converted to a current output signal. The nominal +24 V DC module supply voltage powers the input side of the 7B39. The oscillator on the input side provides the square wave carrier signal used by the modulator and also drives the power transformer. The signal at the secondary of the transformer is used in the demodulator and is also converted to a DC voltage that powers the circuit on the module's output. The floating isolated current output of Model 7B39 is fully protected to 120 V rms line voltage.