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SCM5B35

Linearized, 4-Wire RTD Input Signal Conditioners, Bandwidth 4 Hz

In RTD temperature measurement applications requiring a very high level of accuracy, the SCM5B35 4-Wire RTD input module offers a significant advan-tage over 3-wire measurement techniques. The SCM5B35 measures only the voltage dropped across the RTD and almost completely ignores the resistance or length of the RTD lead wires. The SCM5B34 3-Wire RTD module provides lead resistance compensation, but requires equal lead resis-tances, while the SCM5B35 does not require matched lead resistances.

Each SCM5B35 RTD input module provides a single channel of RTD input which is filtered, isolated, amplified, linearized, and converted to a high-level analog voltage output. This voltage output is logic switch controlled, which allows these modules to share a common analog bus without the requirement of external multiplexers.

The SCM5B modules are designed with a completely isolated computer side circuit which can be floated to ± 50 V from Power Common, pin 16. This complete isolation means that no connection is required between I/O Common and Power Common for proper operation of the output switch. If desired, the output switch can be turned on continuously by simply connecting pin 22, the Read-Enable pin, to I/O Common, pin 19.

RTD excitation is provided from the module by a precision current source. The excitation current is available on two leads which are separate from the two input signal measuring leads. The excitation current does not flow in the input signal leads, which allows RTD measurement to be totally independent of lead resistance. The excitation current is very small (0.25 mA for 100 Ω Pt and 120 Ω Ni and 1.0 mA for 10 Ω Cu) which minimizes self-heating of the RTD.

Signal filtering is accomplished with a six-pole filter which provides 95 dB of normal-mode rejection at 60 Hz and 90 dB at 50 Hz. Two poles of this filter are on the field side of the isolation barrier, and the other four are on the computer side. After the initial field-side filtering, the input signal is chopped by a proprietary chopper circuit. Isolation is provided by transformer coupling, again using a proprietary technique to suppress transmission of common mode spikes or surges. The module is powered from + 5 VDC, ± 5%.

A special input circuit on the SCM5B35 modules provides protection against accidental connection of power-line voltages up to 240 VAC.

Circuit diagram Dataforth SCM5B35

Block Diagram SCM5B35



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9 Modules for Type SCM5B35:

ModuleInputDescription
SCM5B35-01 -100°C to +100°C SCM5B35 Isolated Linearized 4-Wire RTD Input Module with Voltage-Output
SCM5B35-02 0°C to +100°C SCM5B35 Isolated Linearized 4-Wire RTD Input Module with Voltage-Output
SCM5B35-03 0°C to +200°C SCM5B35 Isolated Linearized 4-Wire RTD Input Module with Voltage-Output
SCM5B35-04 0°C to +600°C SCM5B35 Isolated Linearized 4-Wire RTD Input Module with Voltage-Output
SCM5B35-05 -100°C to +200°C SCM5B35 Isolated Linearized 4-Wire RTD Input Module with Voltage-Output
SCM5B35C-01 0°C to +120°C SCM5B35 Isolated Linearized 4-Wire RTD Input Module with Voltage-Output
SCM5B35C-02 0°C to +120°C SCM5B35 Isolated Linearized 4-Wire RTD Input Module with Voltage-Output
SCM5B35C-03 0°C to +160°C SCM5B35 Isolated Linearized 4-Wire RTD Input Module with Voltage-Output
SCM5B35N-01 0°C to +300°C SCM5B35 Isolated Linearized 4-Wire RTD Input Module with Voltage-Output

Specifications

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  • Input: RTD
  • Output: 0 … 5 V or 0 … 10 V
  • Bandwidth 4 Hz
  • Isolation 1500 Vrms
  • Input protection 240 Vrms
  • Input Resistance 50 MOhm
  • Accuracy ± 0.06°C to ± 0.36°C
  • Linearity ± 0.025%
  • ANSI/IEEE C37.90.1 Input protection
  • CMR 160dB
  • True 3-way isolation
  • NMR: 95/90dB at 60/50Hz
  • Power Supply +5 VDC
  • Operating Temperature Range -40°C … +85°C
  • Mix and Match Types on Backpanels possible
  • Dimensions 58 x 57 x 15 mm
  • Optional DIN Rail Mounting
  • CSA certified, CE and ATEX compliant
  • Wide range of accessories
  • Special Solutions on request