5B34 データシートの表示（PDF） - Analog Devices

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5B34

Isolated Linearized RTD Input

Analog Devices 

GENERAL DESCRIPTION

The 5B34 is a single-channel signal conditioning module that

amplifies, protects, filters, linearizes, and isolates a wide variety

of two and three-wire RTDs. For true four-wire RTD

measurements please refer to the 5B35 model.

The 5B34 protects the computer side from damage due to field-

side over-volatge faults. The module withstands 240 V rms at

the input terminals without damage thereby shielding the

internal computer-side circuitry from field-side over-voltage

conditions. In addition, the 5B34 is mix-and-match and hot

swappable with all other 5B Series input modules, so can be

inserted or removed from any socket in the same backplane

without disrupting system power.

Two identical sources provide excitation current for the RTD.

For three-wire RTDs, the second current flows through the

third RDT lead so as to cancel the effects of (equal) lead

resistance; this current also flows through a stable resistor laser-

trimmed to the RTD value that sets the differential amplifier

input and (module) output to zero volts at that scale point. The

current sources and the amplifier input are protected to

withstand input over-voltage up to 240 V rms.

A differential chopper-stabilized input amplifier provides stable

gain and exceptionally low drift. This allows the use of very low

RTD excitation current to minimize self-heating and preserve

.

5B34

measurement accuracy. Along with module gain and zero

settings, a feedback linearizer is laser-trimmed. Custom versions

of 5N34 can be laser-trimmed to meet special requirements.

Internal multi-pole low-pass filtering with a four-Hz cutoff (-

3dB) enhances normal-mode (noise on signal) and common-

mode (noise on signal return) rejection at 50/60 Hz, enabling

accurate measurement of small signals in high electrical noise.

Signal isolation by transformer coupling uses a proprietary

modulation technique for linear, stable and reliable

performance. The differential input circuit on the field side is

fully floating, eliminating the need for any input grounding. 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. The

output common must be kept within +3V of power common.

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 power common as it is

on the 5B01 and 5B08 backplanes.

.

Figure 2

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