DATAFORTH

A Burr-Brown Company

®

48

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SCM5B33

Isolated True RMS Input Modules

FEATURES

q INTERFACES RMS VOLTAGE (0 – 300V) OR RMS CURRENT (0 – 5A)

q DESIGNED FOR STANDARD OPERATION WITH FREQUENCIES OF

45HZ TO 1000HZ (EXTENDED RANGE TO 20Khz)

q COMPATIBLE WITH STANDARD CURRENT AND POTENTIAL

TRANSFORMERS

q INDUSTRY STANDARD OUTPUTS OF EITHER 0-1MA, 0-20mA,

4-20MA, 0-5V OR 0-10VDC

q

±0.25% FACTORY CALIBRATED ACCURACY (ACCURACY CLASS

0.2)

q 1500 VRMS CONTINUOUS TRANSFORMER BASED ISOLATION

q INPUT OVERLOAD PROTECTED TO 480V MAX (PEAK AC & DC) OR

10A RMS CONTINUOUS

q ANSI/IEEE C37.90.1-1989 TRANSIENT PROTECTION

q REGULATORY COMPLIANCE (TO BE DETERMINED)

DESCRIPTION

Each SCM5B33 True RMS input module provides a single channel of AC

input which is converted to its True RMS dc value, filtered, isolated,

amplified, and converted to a standard process voltage or current output

(Figure 1).

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.

The field voltage or current input signal is processed through a pre-amplifier

and RMS converter on the field side of the isolation barrier. The converted dc

signal is then chopped by a proprietary chopper circuit and transferred across

the transformer isolation barrier, suppressing transmission of common

mode spikes and surges. The computer side circuitry reconstructs, filters and

converts the signal to industry standard outputs. Modules are powered from

+5VDC,

±5%.

For current output models an external loop supply is required having a

compliance voltage of 14 to 48VDC. Connection, with series load, is between

Pin 20 (+) and Pin 19 (-).

FIGURE 1. SCM5B33 Block Diagram.

+In

AC Source

–In

**

**

**

–EXC

Backpanel

Term Block

6

5

3

Surge

Suppression

and

Protection

Pre-Amp,

Conversion

*

* Current Input Models Only

Add Jumpers for Current Input Modules

(provided with SCM5B33-06, 07)

Isolated

Field-Side

Power

4

3

2

1

+EXC

–V

+V

I

IN

4

–V

LPF

+V

Power

Oscillator

Isolated

Computer-Side

Power

V

20

22

I/O Common

RD EN\

+5V

17

16

Power Common

19

Isochopper™

Amplifier

Pat Pending