Bradley Smoker PLC-5 Selecting I/O Module Density, Choose this Type, Explanation, Module Examples

2-2Selecting and Placing I/O

	Guidelines for Selecting I/O Modules
Choose this Type of	For these Types of Field Devices or Operations	Explanation
I/O Module	(examples)

Discrete input module	Selector switches, pushbuttons, photoelectric eyes, limit
and block I/O module	switches, circuit breakers, proximity switches, level
	switches, motor starter contacts, relay contacts,
	thumbwheel switches

Input modules sense on/off or opened/closed signals. Discrete signals can be either ac or dc.

Discrete output module	Alarms, control relays, fans, lights, horns, valves, motor
and block I/O module	starter, or solenoids

Output module signals interface with on/off or opened/closed devices. Discrete signals can be either ac or dc.

Analog input module	Temperature transducers, pressure transducers, load cell
	transducers, humidity transducers, flow transducers, and
	potentiometers

Convert continuous analog signals into input values for the PLC controller.

Analog output module	Analog valves, actuators, chart recorders, electric motor	Interpret PLC controller output to analog signals
	drives, analog meters	(generally through transducers) for field devices.
Specialty I/O modules	Encoders, flow meters, I/O communication, ASCII, RF type	Are generally used for specific applications such as
	devices, weigh scales, bar-code readers, tag readers,	position control, PID, and external device
	display devices	communication.

Selecting I/O Module Density

The density of an I/O module is the number of controller input or output image-table bits to which it corresponds. A bidirectional module with 8 input bits and 8 output bits has a density of 8. I/O module density helps determine your I/O addressing scheme. See chapter 4 for more information about I/O addressing.

Use these guidelines for selecting I/O module density:

Choose this I/O Density	If You
8-point I/O module	• currently use 8-point modules
	• need integral, separately-fused outputs
	• want to minimize cost per module
16-point I/O module	• currently use 16-point modules
	• need separately-fused outputs with a special
	wiring arm
32-point I/O module	• currently use 32-point modules
	• want to minimize number of modules
	• want to minimize the space required for I/O
	chassis
	• want to minimize cost per I/O point

Publication 1785-UM012D-EN-P - July 2005