In RTD temperature measurement applications requiring a very high level of accuracy, the SCM5B35 4-Wire RTD input module offers a significant advantage 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 resistances, 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 ±50V 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 (0.25mA for 100 Ohm Pt and 120 Ohm Ni and 1.0 mA for 10 Ohm Cu) which minimizes self-heating of the RTD.

Signal filtering is accomplished with a six-pole filter which provides 95dB of normal-mode rejection at 60Hz and 90dB at 50Hz. 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 +5VDC, ±5%.

A special input circuit on the SCM5B35 modules provides protection against accidental connection of power-line voltages up to 240VAC.
  • Interfaces to 100 Ohm Platinum, 10 Ohm Copper, or 120 Ohm Nickel RTDs
  • True 4-Wire Input
  • Linearizes RTD Signal
  • High-Level Voltage Output
  • 1500Vrms Transformer Isolation
  • ANSI/IEEE C37.90.1 Transient Protection
  • Input Protected to 240VAC Continuous
  • 160dB CMR
  • 95dB NMR at 60Hz, 90dB at 50Hz
  • CSA Certified, FM Approved, CE and ATEX Compliant
  • Mix and Match SCM5B Types on Backpanel
Linearized 4-Wire RTD Input Modules

SCM5B35 Devices


Part Number Input ConfigurationRTD TypeInput RangeOutput RangeMechanical Format
4 Wire 100 Ohm Platinum -100 to 100 (°C) 0 to +5 V Modular plug-in-board
4 Wire 100 Ohm Platinum -100 to 100 (°C) 0 to +10 V Modular plug-in-board
4 Wire 100 Ohm Platinum 0 to 100 (°C) 0 to +5 V Modular plug-in-board
4 Wire 100 Ohm Platinum 0 to 100 (°C) 0 to +10 V Modular plug-in-board
4 Wire 100 Ohm Platinum 0 to 200 (°C) 0 to +5 V Modular plug-in-board
4 Wire 100 Ohm Platinum 0 to 200 (°C) 0 to +10 V Modular plug-in-board
4 Wire 100 Ohm Platinum 0 to 600 (°C) 0 to +5 V Modular plug-in-board
4 Wire 100 Ohm Platinum 0 to 600 (°C) 0 to +10 V Modular plug-in-board
4 Wire 100 Ohm Platinum -100 to 200 (°C) 0 to +5 V Modular plug-in-board
4 Wire 100 Ohm Platinum -100 to 200 (°C) 0 to +10 V Modular plug-in-board
4 Wire 10 Ohm Copper 0 to 120 (°C) 0 to +5 V Modular plug-in-board
4 Wire 10 Ohm Copper 0 to 120 (°C) 0 to +10 V Modular plug-in-board
4 Wire 10 Ohm Copper 0 to 120 (°C) 0 to +5 V Modular plug-in-board
4 Wire 10 Ohm Copper 0 to 120 (°C) 0 to +10 V Modular plug-in-board
4 Wire 10 Ohm Copper 0 to 160 (°C) 0 to +5 V Modular plug-in-board
4 Wire 10 Ohm Copper 0 to 160 (°C) 0 to +10 V Modular plug-in-board
4 Wire 120 Ohm Nickel 0 to 300 (°C) 0 to +5 V Modular plug-in-board
4 Wire 120 Ohm Nickel 0 to 300 (°C) 0 to +10 V Modular plug-in-board

Frequently Asked Questions


Can Dataforth provide calibration reports for modules I purchased?
Yes we can provide calibration reports for the modules that you purchased.

You can either
a) visit https://www.dataforth.com/TestDataReport.aspx to search for Test Report Datasheets by Serial Number or
b) you can send us a list of model numbers and their serial numbers to support@dataforth.com

Analog Devices announced a last time buy and discontinuance of their signal conditioning modules. Can I replace them with Dataforth signal conditioning modules?
Yes, in general, Dataforth signal conditioning modules are a direct replacement for all Analog Devices signal conditioning modules. e.g. "SCM5B35-xx: Linearized 4-Wire RTD Input Modules" will replace Analog Devices "5B35: Isolated 4 Wire RTD Input Signal Conditioning Module".

Please note that Dataforth signal conditioning modules are RoHS II compliant.

Do you have an MTBF figure for the SCM5B39? What are the main failure modes?
The failure rate calculations for our SCM5B modules can be found in our application note AN503: https://www.dataforth.com/catalog/pdf/an503.pdf

There are no dominant failure modes.

Will the isolation on the SCM5B modules support a discharge of 1500VDC without damaging anything connected to the output?
Yes, the SCM5B modules are isolated up to 1500 Vrms, which means that if the common mode voltage between the field side and system side is limited to 1500Vrms, the device will be protected.

However, the input protection for SCM5B modules (i.e., the voltage across the +IN and -IN input terminals) is 240Vrms max.

How do I convert an RMS voltage to its corresponding peak voltage?
To convert an RMS voltage to its corresponding peak voltage, you simply take the RMS voltage value and multiply it by the square root of 2, or roughly 1.414.

For example, 1500Vrms corresponds to a peak voltage of 1500 * 1.414 = 2121 Vp

Do you have any SCM5B modules with a 50kHz bandwidth?
None of our standard SCM5B modules have a 50kHz bandwidth. However, it is possible to order a custom SCM5B module with 50kHz bandwidth. Keep in mind that new customs require a 10 pc minimum order and are subject to extra design fees.

What is the recommended power supply for Dataforth SCM5B and 8B modules?
The recommended power supply for the Dataforth SCM5B and 8B modules are the linear power supplies in our SCMXPRT/SCMXPRE series. The SCMXPRT/SCMXPRE power supplies output 5V and have options for 1A output current (SCMXPRT-001) or 3A output current (SCMXPRT-003).

The SCMXPRE series is identical to its SCMXPRT counterpart, but is configured for European voltage standards.

The SCMXPRT-001/SCMXPRE-001 both have the option for DIN rail mounting as well (SCMXPRT-001D/SCMXPRE-001D).

Other power supplies that meet that power requirements of the SCM5B and 8B modules can be used as well, but it is strongly recommended to use a linear power supply rather than a switch-mode power supply. Switching power supplies can add noise artifacts to the output of your modules.

If the input range of my signal conditioner is -1V to +1V and the output range is 0 to 10V, does this mean that it ignores polarity?
A signal conditioner with these I/O ranges does not mean that the module ignores the polarity of your voltage input. The output of voltage input modules are scaled linearly, meaning an input of -1V would correspond to an output of 0V, an input of 0V would correspond to an output of 5V, an input of +1V would correspond to an output of 10V, and so on.

Do SCM5B modules with outputs scaled up to 10V have separate power requirements from their 5V counterparts?
No, all SCM5B modules have the same power requirements (5VDC) regardless of their I/O specifications. The power supply current draw of different products in the SCM5B line may vary.

Can I use an SCM5B module with my OM5-BP-SKT-C?
Yes, any of our SCM5B modules are able to be mounted and operated on Omega's OM5-BP-SKT-C board.

Is the SCMXPRT-003 DIN rail mountable?
The SCMXPRT-001 has an option for DIN rail mounting (part number: SCMXPRT-001D) but the SCMXPRT-003 does not. Instead, it can be mounted on the SCMXRK-002 which is a 19 inch metal rack for mounting the SCMXPRT-003 as well as various Dataforth backpanels and the SCMXIF interface board.

Do I need to purchase the SCMXCJC with my SCMPB03?
No, the SCMPB03 comes with the CJC built into the backpanel.

Should I ground my sensor wire shield to the 10-32 ground post on the SCMPB01?
It is not recommended to ground the sensor wire shield to the 10-32 ground post on the SCMPB01 because that is the system side ground, while the sensor wire is on the field side. The sensor wire shield should be grounded to the field side ground, which varies based on the signal conditioner you are using. Please see the "Shield Grounding" application note for more information.

I just received an SCMPB01 back panel. How should I configure jumpers J1 through J4 for my application?
The factory configuration for jumpers J1 through J4 is the optimal configuration for most applications. If for some reason this jumper configuration will not work/is not working in your application, see our application note AN502 "Ground Connections and Host System Interfaces" for other valid jumper configurations and what situations you would use them.

What is the required resistance for jumpers J1 through J4 on my SCM5B backpanel?
J1-J4 on the SCM5B backpanels are jumper cables, so they should have 0 ohm resistance.

How does the load resistance of a module affect the noise at the output?
Noise at the output of a module is independent of load resistance.

If I purchase a backplane with no CJC, will I still be able to use modules that require the CJC enable jumper to be installed?
Yes. Backplanes with no CJC will still come with the CJC enable installed on the backplane.