5B35

The 5B35 is a single-channel signal conditioning module that amplifies, filters, isolates and protects a wide variety of four-wire RTDs. The module provides a linearized, highly accurate output of 0 to +5V.

Accurate and Stable Performance The four-wire configuration of the 5B35 supplies RTD excitation from a precision, protected current source: two RTD wires carry the excitation current and two wires of 5B35 serve as signal-input leads that measure the voltage across the RTD. Because no excitation current flows through the signal input leads, the length or
resistance of the leads creates little or no RTD measurement error. A low-drift chopper-stabilized differential amplifier of 5B35 allows use of very low excitation current to minimize error due to RTD self heating. The amplifies low input offset drift of +0.01oC/oC and gain drift of +30ppm/oC. Assure accuracy over the full operating temperature range.

True Three-Port Isolation The floating, differential input circuit of 5B35 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) of 5B35 includes common-mode rating of: 1500V rms between input and output and input and power; 250V rms between power and output no return path is required between the power and signal output commons.

Filtering and Protection An optimized five-pole Butterworth filter of 5B35 (with a 4-Hz bandwidth) provides 116dB of normal-mode rejection (noise on signal) at 60 Hz and 108 dB at 50 Hz. Output noise of 5B35 is an exceptionally low 0.3 Mv p-p in a 100 kHz bandwidth and 6 mV p-p in a 5 MHz bandwidth.

The 5B35 protects the computer side from damage due to fieldside over-voltage faults. The 5B35 withstands 240V rms at the input terminals without damage, thereby shielding the internal computer-side circuitry from field-side over-voltage conditions. In addition, the 5B35 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.

A series output switch of 5B35 eliminates the need for external multiplexing in many applications. The switch is turned on by an active-low enable input. If the switch of 5B35  is to be on at all times,the enable-input should be grounded to power common as it is on the 5B01 and 5B08 backplanes.