GE IC697ALG230 Base Converter Module Features Expansion Bus

High Level Analog Input System Modules

Three module types are included in the High Level

Analog Input subsystem: a Base Converter module, a

Current Expander module, and a Voltage Expander

module.  A typical subsystem will use a Base Convert

er module and (if required) one or more expander modules.

•Base Converter module - catalog number

IC697ALG230

This module has eight differential inputs and

an expansion port.  Each input can be individu

ally configured for either voltage or current.

Each of the input channels also has individual

user scaling.

On-board load resistors are included for normal

input current ranges up to Ç 40 mA.  If other

current ranges or different resolution is re

quired, external resistors may be used.

Standard system configurations for Ç 10 volts

and 4 to 20 mA are available.  These, and other

lower input ranges, can be scaled to engineer

ing units with the user scaling feature.

•Expander Modules

Up to seven Expander modules can be daisy

chained off the Base Converter module to in

crease the number of inputs of the total subsys

tem up to a maximum of 120.

The Base Converter module accepts any mix of

the two Expander module types.

A common user scaling factor applies to all in

puts on each Expander module, however each

Expander module may be individually scaled as required.

•Current Input Expander module - catalog number

IC697ALG440

The Current Expander module has 16 current

inputs each accepting up to Ç 20 mA.

•Voltage Input Expander module - catalog number

IC697ALG441

The Voltage Expander module has 16 differen

tial voltage inputs each accepting up to Ç 10V signals.

Expansion Bus

The bottom six terminals (35 through 40) on the ter

minal board on the Base Converter and Expander

modules make up an expansion bus for connecting

input Expander modules to the Base Converter mod

ule.  An analog multiplexer on the Expander module

acts as a switching circuit to connect analog inputs,

one at a time, to the A/D (Analog to Digital) converter

on the Base Converter module.

Input Sampling Techniques

The objective of the input sampling technique for the

analog subsystem is to provide 8 input channels on

the base module that have a fast (approximately 3 ms)

update rate and additional expander channels that are

updated less frequently, but have a lower cost per

channel.

Operation is such that the base module initially up

dates all eight channels plus one expander channel.

On each successive scan all eight channels of the base

converter are again updated - plus the next expander

channel in sequence.  After 16 analog input scans all 16

channels of the first expander have been sampled; on

the next scan, all eight base converter channels plus

the first channel of the next Expander module are

scanned.

This sampling technique continues until all available

expander channels (16 x number of Expander mod

ules) have been scanned, at which time the sequence

starts over.  The number of analog scans required to

include sampling of all expander channels is equal to

the total number of Expander modules x 16 (16 chan

nels per Expander module) in the system.

With no Expander modules present, each base con

verter channel is updated once every 2.4 milliseconds.

With one or more Expander modules present, this

update time increases to 2.8 milliseconds.

Each expander channel is updated every 2.8 x N ms

(where N = total number of Expander channels pres

ent).  Note that the scan sequence is free running and

it cannot be synchronized with any external event.

Also note that all inputs of an Expander module will be

scanned even if they are not being used.