Rockwell-automation 1791-XXXX Discrete I/O AC and DC Block I/O Input a Manual de usuario descargar pdf (Pagina 14)

I/O Interface and System Design

Chapter 2

2-4

Example: You want to use an ac 2–wire Bulletin 871C Proximity Switch

for an input to a block I/O module. To determine if the switch is

compatible with the block, verify the following:

I

block-off

> I

leakage-switch

V

supply

- V

switch-on

> V

block-on

where:

I

blockoff

= minimum off-state current of block input

I

leakageswitch

= maximum off-state leakage current of proximity switch

V

supply

= minimum value of supply voltage

V

switchon

= maximum on-state voltage drop of proximity switch

V

blockon

= minimum on-state voltage specification

Simplified schematics of ac and dc input circuits are shown in Figure 2.3

and Figure 2.4.

Figure 2.3

Simplified

Schematic of ac Input Circuit

Opto

Isolation

Input

Filter

Input

Indication

LED

(logic)

System

Circuitry

3.16KΩ

27KΩ

27KΩ

33Ω

33V

0.2µF

79-132V ac

Input

Common

L1

L2

Figure 2.4

Simplified

Schematic of Sinking dc Input Circuit

Opto

Isolation

Input

Filter

Input

Indication

LED

(logic)

System

Circuitry

+10-30V dc

+

464Ω

2.8KΩ

DAN212K

Return

Common

-

Input

18555

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