Selecting a PLCSubject: Industrial AutomationGroup members:-1. Ghassan Maan2. Asif Ali Khan3. Radwan Seannaro4. Nurul Balqis

INTRODUCTIONIn selecting a PLC, we need to consider the required input, output, and function of controller.

Types of controller : Rack , Mini, Micro, or software. Need to consider the followings when choosing a controller;

-Num of logic input/output.-Memory required, 1K or few bytes.-Scan time, (price)- software, Availabilityof programming.-Comunications, serial or network.

PROCESS OF SELECTING A PLC1. Understand the process to be controlled

-num. of input/output-how the process is to be controlled?-special needs, such as distance between parts of the process.

2. If not already specified, a single vendor should be selected. Factors considered:--manuals & documentation-training-the range of product available-shaping time for emergency replacement

3. Plan the ladder logic for the controls

4. Count the program instruction5. Look for special program needs and check

the PLC model6. Estimate the cost for suitable hardware,

programming software, cables, manuals, training , or ask a quote from vendor or etc.

SPECIAL I/O MODULES:-Many different I/O modules are availableCommercial selection is very largeMost vendor offer competitive modulesSome modules offer only few supplier such ad omron

PLC CPU

Different types of PLC CPU availableThe basic formula of selection is the price or

performance

Programmers:-3 Basic Categories:-PLC softer for personal computersHand held unitsSpecializes programming units

Counters• Each card will have 1 to 16 counters at speeds up to 200KHz.• The counter can be set to zero, or up/down, or gating can occur with

an externalinput.Thermocouple• Thermocouples can be used to measure temperature, but these low

voltagedevices require sensitive electronics to get accurate temperature

readings.Analog Input/Output• These cards measure voltages in various ranges, and allow

monitoring of continuousprocesses. These cards can also output analog voltages to help controlexternal processes, etc.

PID modules• There are 2 types of PID modules. In the first the CPU does the

calculation, in the second, a second controller card does the calculation. - when the CPU does the calculation the PID loop is slower.

- when a specialized card controls the PID loop, it is faster, but it costs less.

• Typical applications - positioning workpieces.Stepper motor• Allows control of a stepper motor from a PLC rack.Servo control module• Has an encoder and amplifier pair built in to the card.Diagnostic Modules• Plug in and they monitor the CPU status.Specialty cards for IBM PC interface• Siemens/Allen-Bradley/etc. have cards that fit into IBM buses, and

will communicatewith PLC’s.

SUMMARY•Suppliers and products should be evaluated•Simplifying maintenance – single supplier•Time and memory requirements can be estimated•Special I/O modules can be selected to suit project needs