PLC’s Flashcards
The XIC instruction is true when the external input device that controls it ________ (provides/does not provide) voltage.
Provides
The examine if off instruction is true when the external input device that controls it _______ (provides/does not provide) voltage.
Does not provide
What binary bit will be represented when the XIO instruction is false?
1
If a normally closed push button (which is not pressed) is wired to a PLC as a stop button, a logic _______ (true/false) condition will exist at the corresponding XIO ladder logic instruction.
False
List the 4 major sections of a PLC system
Input
CPU
Programming
Output
List 3 main reasons PLC’s are preferred over other control sections
Flexibility; easy to add control sections
Reliably; no moving parts
Accuracy; timers are more accurate than conventional
List three types (categories) of devices that can be wired to an input
Discrete; PB’s, limit switches, float switches
Analogue; potentiometer, rheostat
Pulse; shaft encoder
What are the two main types of PLC memory?
RAM; executive, factory set, non volatile
ROM; user, volatile
List two factors that should be taken into account regarding the physical environment for a PLC installation
Temperature
Humidity
Dust
Shock and vibration
List two devices that can be used for programming a PLC
PC
Laptop
Handheld programmer
Name the device that is used in both input and output module circuitry to provide electrical isolation
OPTO isolator (coupler)
What is the best practice for grounding a single shielded cable?
Ground/bond at one end only (controller)
NO SHIELD IN THE FIELD
List the three main PLC programming instructions used with relay ladder logic
XIC; examine if closed
XIO; examine if open
OTE; output energize
What is the difference between an internal dummy relay instruction and a real output energize instruction?
There is no physical field connection. It only exists in the logic program
While in run mode, a Micrologix 1000 PLC will allow an instruction to be changed from XIC to XIO. (T/F)
False
While in run mode, a PLC will allow a timers preset value to be changed. (T/F)
True
A “single scan test” mode is a convenient way of testing the logic and function of your program while you are still offline. (T/F)
False
Output modules having ‘dry contacts’ may switch both AC and DC loads. (T/F)
True
The user memory (program) will normally be retained in memory on the PLC’s in our lab if the normal AC power supply is lost. (T/F)
True
An on-delay timer’s address could be O:0/1. (T/F)
False
An output thats addressed B:0/2 can be wired to an indicating light in the field. (T/F)
False
Why would it not be considered good practice to wire a normally open stop button to an XIO.
Its not fail safe. It wont stop if PB fails or a loose wire occurs
A sinking type input module will ______ (send/receive) current from/to the input field device.
Receive
What is an MCR sometimes used for?
Low voltage protection
