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Hardware -- Discrete Input Modules


The purpose of the discrete input module is to read the status of field devices. When a voltage is detected on the terminal of an input module with respect to common, the corresponding status light is energized, and during the processor scan, the value of 1 is placed into the input data table. Examples of input devices include switches, pushbuttons, or auxilliary contacts on a motor starter. The Removable Terminal Block (RTB) can be detatched from the module if the locking tab is pushed up. The enclosure of the RTB will also slide off the terminal block for easy access to the terminals.


Please answer the following questions:


  1. What is the catalog number of your DC Input module?



  1. Name at least three field devices that can be connected to the DC Input module?



  1. What do the status lights indicate on the front of the DC Input Module?



  1. What is the slot number of the DC Input module at your station.





Discrete Output Modules


The purpose of the discrete output module is to control field devices. The discrete output module requires power from an external source. When a 1 is placed into the output tag of the ControlLogix (in run mode), a status light is energized on the module, and a connection is made between the source, and the corresponding output terminal. Examples of output devices include: lights, solenoids, motor starter coils, and contactors. If you have an inductive load as the output, be sure to use the proper surge supression.


Please answer the following questions:


  1. What is the catalog number of your DC Output module?


  1. Name at least three field devices that can be connect to the DC Output module:


  1. What do the status lights indicate on the DC Output module?


  1. What is the slot number of the DC Output Module?


  1. If the load on the DC output card is inductive, what should be done across the load to minimize the effects of inductive kick?






Analog Modules


Analog modules are used to control and read the status of analog devices. Analog devices have a range of states instead of just on/off states like discrete devices.


Some analog modules have switches which determine whether the input channels are to be set up for voltage or current. Some analog modules are configured through software.


Examples of analog inputs include: Potentiometer, Pressure Transducers, Variable speed drives, and with a thermalcouple module, temperature can be read into the processor's memory.


Examples of analog outputs include: Meters, Variable Speed Drives, Valve Positioners, and chart recorders.


An analog signal cannot be expressed with a single bit, and therefore analog values will consume a word of memory. For our class, we will use the Analog module on the Flex I/O chassis.


Please answer the following questions:



  1. What is the catalog number of your analog module?



  1. How many channels of Input, and how many channels of Output are available on this module?



  1. How do you set up the input channels to accept either a current or a voltage input?



  1. What range voltage or current will the Input channels accept on your module? What range of voltage will the output channels accept?



  1. Name at least three devices that are analog inputs:



  1. Name at least three field devices that are analog outputs:





An Analog Module – 1747-NIO4V




The Chassis


The chassis is the device which holds modules. Allen Bradley makes the ControlLogix chassis available in 4, 7, 10, 13, and 17 slots.


Here are some chassis:



The PLC-5 Chassis (With modules): (For dip switch settings on this chassis, refer to page 4-1 and 4-2 of the PLC-5 Quick Reference Guide.)




The SLC-500 Chassis (With modules):




The ControlLogix Chassis (With Modules):




The Flex Chassis:




The Power Supply


The power supply supplies power to the modules on the backplane. Generally power from field devices DOES NOT come from the power supply. The power supply only provides control power to modules on the backplane. Power for field devices come from a separate source which is connected to the output module. The power supply merely provides the power needed to shut a contact, or fire a triac or transistor to pass power from this external source to the field device. On the back of the power supply, a jumper is used to set the voltage range.


Please answer the following questions:



  1. Where does power come from to power field devices such as solenoids, lights, and motor starters?


  1. What must be set up on a new power supply before it can be placed into service?


  1. How many amps will your power supply provide to the backplane?


  1. What ist he catalog number of your power supply?





The Processor



The processor is the main part of your ControlLogix system. The processor is where the program is stored that reads the status of your equipment, and based on certain status, makes a decision on what to control. For example: The processor is reading the status of a switch. When the operator energizes the switch, the processor might call for solenoid to energize that extends a cylinder. When the cylinder reaches the end of it's travel, it might close a limit switch. The processor will see that a limit switch has been closed, and shut off the solenoid. Although traditionally the processor usually is placed in slot 0, it can be placed anywhere in the chassis, as long as the program is setup for the processor to be in that slot. You can also use as many processors as you like in a chassis (not to exceed the limitation of the power supply)


The processor consists of several components:


  1. The battery: The battery retains the processor's program when the PLC is powered down. Certain AB documentation states that the shelf life of the battery is up to 2.5 years. When the battery is low, you will see a BATT light on the front of the processor. A minor fault bit is also set in the memory of the processor when the battery is low or missing.


  1. On the front of the processor, you will find several status lights:

    1. RUN – Indicates when when processor is in RUN Mode

    2. OK – If flashing red, usually indicates a software problem. Go online to get a description of the fault. You will find the description in the Controller Properties on the FAULT tab. If the fault light is solid red, this ucould indicate a hardware problem. You can try the following: reseat the processor, clear memory and reload program, or replace processor.

    3. BATT-- Indicates the battery is low or missing

    4. IO – If flashing indicates the Processor lost it's connection with at least one I/O device.

    5. FORCE – If flashing indicates forces are installed but not enabled... If solid indicates forces are installed, and enabled in the processor. This indicator is not available on all ControlLogix processors.

    6. RS232 – This light will flicker as data is transferred over the RS232 port (channel 0).


  1. The Key Switch:

    1. Run Mode: In this position, certain tag values can be modified, but ladder logic cannot. The mode of the processor cannot be changed to program mode from the On line tool bar in RSLogix. When the switch is in run mode, a program cannot be downloaded to the processor.

    2. Program Mode: In this position, the ladder is not executing. Changes can be made to the ladder diagram or to data files. The processor cannot be changed to run mode from the on line tool bar in RSLogix while the switch is in this position.

    3. Remote Mode: When the key switch is in Remote Mode, the mode of the processor can be changed from RSLogix (Program or Run). On line editing is allowed.







The ControlLogix Processor: