5B42 Isolated, Process Current Input

The floating, differential input circuit on the field side eliminates the need for any input grounding. Signal and power isolation by transformer coupling uses a proprietary modulation technique for linear, stable and reliable performance. A demodulator on the computer side of the signal transformer recovers the original signal, which is then filtered and buffered to provide a low-noise, low-impedance output signal. True three-port isolation (Input-Output-Power) includes common-mode ratings of: 1500 V rms between input and output and input and power; 250 V rms between power and output - no return path is required between the power and signal output commons.

Accurate and Stable Performance

The 5B42 maintains accuracy over the wide operating temperature range of -40°C to +85°C through design for low parameter drift. This enables the module to provide output offset drift of only ±5 µV/°C and gain drift of just ±25 ppm/°C.

Why an Internal Current Sense Resistor

The 5B42 offers significant advantages over signal conditioners that require an external current sense resistor. First, an external resistor is not protected from accidental connection to a 240 V rms power line. Next, the external resistor tolerance must be added to the conditioners specified errors. In contrast, the 5B42 is calibrated and specified with its internal 25 Ω sense resistor. Further, the 5B42 signal input, loop supply and the sense resistor are all protected against accidental application of excess voltages up to 240 V rms. Finally, there is no need to install an external sense resistor on the backplane, but if one is installed it will not affect 5B42 performance.

Filtering and Protection

The 5B42 contains an optimized five-pole low-pass filter with a -3 dB bandwidth at 100-Hz that provides a low-overshoot step response and exceptionally low noise of 200 µV pk-pk in a 100 kHz bandwidth. Attenuation (normal mode rejection) increases at a 90 dB/decade rate beyond 100 Hz.

The module protects the computer side from damage due to field-side overvoltage faults. The module withstands 240 V rms at the input terminals without damage, thereby shielding the internal computer-side circuitry from field-side overvoltage conditions. In addition, the 5B42 is mix-and-match and hot-swappable with all other 5B Series modules, so can be inserted or removed from any socket in the same backplane without disrupting system power.

Convenience Features

A series output switch eliminates the need for external multiplexing in many applications. The switch is turned on by an active-low enable input. If the switch is to be on at all times, the enable-input should be grounded to output common as it is on the 5B01 and 5B08 backplanes.