Archives

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.

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.

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.

Functions

The High Level Analog Input subsystem for the  Pro

grammable Logic Controller (PLC) accepts analog in

puts of up to Ç10 volts full scale, or 4 to 20 milliamp

current loop signals.  These inputs are converted to

digital form for use by the CPU or other controllers

accessing analog inputs via the VME backplane.

Converted data is presented as 2’s complement (sign

+ 15 bits).  The basic converter is 14 bits resolution (1

part in 16384); an oversampling and averaging tech

nique further enhances this resolution.  Inputs are

protected against transient and steady-state overvol

tage conditions.

Analog inputs use %AI references in the program

mable controller.  A maximum of 8K words of %AI

memory is currently available in the programmable

controller.  Each input channel uses one word (16 bits)

of %AI memory.

Field wiring is made to a removable terminal board

and the module is mechanically keyed to ensure cor

rect replacement with a similar module type in the

field.  I/O references are user configurable without the

use of jumpers or DIP switches on the module.

Configuration is done using the configuration func

tion of the MS-DOS or Windows programming soft

ware running on Windows 95 or Windows NT over

Ethernet TCP/IP or through the SNP port. The Pro

gramming Software configuration function is installed

on the programming device.  The programming de

vice can be an IBM  XT, AT, PS/2  or compatible Per

sonal Computer.

Advantages include:

• Broad range of display sizes from 6″ to 12″

• Choice of Monochrome, Color-STN, or Color-TFT display

• Microsoft Windows® CE operating system

• Expandable memory & Fieldbus cards*

• Compact Flash*

• UL Class 1 Div 2 (A, B, C, D), ATEX Class 1. Zone 2. CE Mark

• Cost-effective replacement for panel operators

• Functions from data collection and trending to system security and alarming

• Built-in web server for access to data, and panels using any standard browser*

• Communication over serial, Ethernet, and communication expansion cards*

• Multi-language support selectable by the operator when the system is online

• Shared tags for increased productivity – applications

developed for QuickPanel View can share tags with other

Machine Edition applications, eliminating the need to

enter the data more than once

• Migration of applications developed with QuickDesigner

• Extensive library of pre-configured animation objects

• 2-year warranty on all models

*Available on select models. See page 2 for availability