Impulse SCM5B35 User Manual

SCM5B35

Linearized 4-Wire RTD Input Modules

Description

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 (Figure 1). 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

120

Ω Ni and 1.0 mA for 10Ω 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

Ω Pt and

Isolated Analog Signal Conditioning Products

SCM5B

▲

Features

 Interfaces to 100Ω Platinum, 10Ω Copper,

or 120

Ω 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

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.

Figure 1: SCM5B35 Block Diagram

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For information call 800-444-7644

Isolated Analog Signal Conditioning Products

SCM5B

Specifications

Module

Input Range Limits 200°C to +850°C (100Ω Pt)

Input Resistance

Normal 50MΩ
Power Off 40kΩ
Overload 40kΩ

Input Protection

Continuous 240Vrms max

Transient ANSI/IEEE C37.90.1

Sensor Excitation Current

100Ω Pt, 120Ω Ni 0.25mA
10Ω Cu 1.0mA

Lead Resistance Effect

100Ω Pt, 120Ω Ni ±0.0005°C/Ω
10Ω Cu ±0.005°C/Ω

CMV, Input to Output

Continuous 1500Vrms max

Transient ANSI/IEEE C37.90.1

CMR (50Hz or 60Hz) 160dB

NMR 95dB at 60Hz, 90dB at 50Hz

Accuracy See Ordering Information

Conformity Error

Stability

Input Offset ±0.01°C/°C

Output Offset ±20µV/°C

Gain ±35ppm of Reading/°C

Noise

Input, 0.1 to 10Hz 0.2µVrms

Output, 100kHz 200µVrms

Bandwidth, 3dB 4Hz

Response Time, 90% Span 0.2s

Output Range See Ordering Information

Output Resistance 50Ω

Output Protection Continuous Short to Ground

Output Selection Time 6µs at C

(to ±1mV of V

Output Current Limit +8mA

Output Enable Control

Max Logic 0 +0.8V

Min Logic 1 +2.4V

Max Logic 1 +36V

Input Current 0,1 0.5µA

Open Input Response

Lead 1,4 Downscale

Lead 2,3 Non-deterministic

Open Input Detection Time 3s

Power Supply Voltage +5VDC ±5%

Power Supply Current 30mA

Power Supply Sensitivity

100Ω Pt, 120Ω Ni ±0.2°C/V
10Ω Cu ±0.5°C/V

Mechanical Dimensions 2.28" x 2.26" x 0.60"

(h)(w)(d) (58mm x 57mm x 15mm)

Environmental

Operating Temp. Range 40°C to +85°C

ATEX Group II, Category 3 20°C to +40°C

Storage Temp. Range 40°C to +85°C

Relative Humidity 0 to 95% Noncondensing

Emissions EN61000-6-4 ISM, Group 1

Radiated, Conducted Class A

Immunity EN61000-6-2 ISM, Group 1

R F Performance A ±0.5% Span Error

ESD, EFT, Surge, Voltage Dips Perfo rmance B

NOTES:

(1) "Ω" refers to the resistance in one lead.

(2) Includes conformity, hysteresis and repeatability.

(3) Conformity error is ±0.05% Span for SCM5B35N-01.

Typical at TA=+25°C and +5V power

(3)

)

OUT

SCM5B35

80°C to +320°C (120Ω Ni)

100°C to +260°C (10Ω Cu)

±0.025% Span

= 0 to 2000pF

load

Ordering Information

Model Input Range Accuracy

ΩΩ

100

Ω Pt **

ΩΩ

Output Range



SCM5B35-01 100°C to +100°C 3, 4 ±0.12°C

(148°F t o +212°F)

SCM5B35-02 0°C to +100°C 3, 4 ±0.06°C

(+32°F t o +212°F)

SCM5B35-03 0°C to +200°C 3, 4 ±0.12°C

(+32°F t o +392°F)

SCM5B35-04 0°C to +600°C 3, 4 ±0.36°C

(+32°F to +1112°F)

SCM5B35-05 -100°C to +200°C 3, 4 ±0.18°C

(-148°F to +392°F)

(1)

(1)

ΩΩ

Ω Cu **

10

ΩΩ

SCM5B35C-01 0°C to +120°C 3, 4 ±0.23°C

(10

Ωat 0°C)

(+32°F to +248°F)

SCM5B35C-02 0°C to +120°C 3, 4 ±0.23°C

Ω at 25°C)

(10

(+32°F to +248°F)

SCM5B35C-03 0°C t o +160°C 3, 4 ±0.32°C

(10

Ωat 0°C)

(+32°F to +320°F)

ΩΩ

Ω Ni **

120

ΩΩ

SCM5B35N-01 0°C t o +300°C 3, 4 ±0.23°C

(+32°F to +572°F)

**RTD Standards

Type Alpha Coefficient DIN JIS

Ω Pt 0.00385 DIN 43760 JIS C 1604-1989

100

120Ω Ni 0.00672
10ΩCU 0.004274







Output Ranges Available

Output Range Part No. Suffix Example

3. 0V to +5V NONE SCM5B35-01

4. 0V to +10V D SCM5B35-01D

(2)

SCM5B

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