Model 5B35 converts the input from a wide variety of RTD types to a linearized, high accuracy output of 0 V to +5 V. The module provides transformer isolation, RTD excitation, RTD lead-resistance compensation, signal filtering and input protection against line voltage connection. A series output switch eliminates the need for external multiplexing. The industry standard 5B Series encapsulated plug-in modular package is
compatible with all 5B backplanes. Modules are powered by +5 V dc, ±5%.
Signal isolation is provided by transformer coupling using a proprietary technique for linear, stable performance. A demodulator on the output side of the signal transformer recovers the input signal, which is filtered and buffered to provide an accurate, low impedance, low noise output.
True three-port isolation includes common-mode voltage of: 1500 V rms between input and output, and between input and power; 250 V rms between output and power.
The modules provide RTD excitation from a precision current source. A low drift, chopper stabilized, differential amplifier design allows for the use of very low RTD excitation currents to minimize accuracy losses from self-heating of the RTD. The low input offset drift of ±0.01°C/°C and gain drift of ±30 ppm/°C assure that accuracy is maintained over a wide operating temperature range.
The four-wire configuration of the 5B35 supplies the RTD excitation current through two leads that are not the signal input leads. Because there is no excitation current in the signal input leads, the lead lengths or resistances have no effect on the RTD measurement.
An optimized five-pole Butterworth filter (with 4 Hz bandwidth) provides 116 dB of normal-mode rejection at 60 Hz and 108 dB at 50 Hz. Output noise is an exceptionally low 0.3 mV p-p at 100 kHz bandwidth and 6 mV p-p at 5 MHz bandwidth.
The input circuit is protected against accidental application of voltages, such as an ac power line, up to 240 V rms continuous.
A series output switch is included to eliminate the need for external multiplexing in many applications. This switch has a low output resistance and is controlled by an active-low enable input. When the output switch is not used, ground the enable input to I/O common to turn on the switch.
