PLC Basics Flashcards
Name some advantages to a PLC-based system
- Increased Reliability
- Flexibility
- Lower Costs
- Communications Capability
- Faster Response Times
- Easier to Troubleshoot
If current flows from the field device to an input circuit, the field device is:
a) Sinking
b) Sourcing
b) Sourcing
Name the three steps in a PLC’s scan process
1) Read inputs
2) Run program
3) Adjust outputs
PLC control output devices based on ____ and ____
Inputs and user-written program
Which task is highest priority in a PLC?
a) Continuous
b) Periodic
c) Event
Event
What is the difference between a scheduled and an unscheduled program?
Scheduled can execute, unscheduled cannot
What does the “3” represent in:
Local:1:I.Data.3
The slot/bit number on the module
What does “local” represent in:
Local:1:I.Data.3
PLC has a single Chassis
What does “I” represent in:
Local:1:I.Data.3
Data reads an input
Variables in a program are local or global?
Local
What is the preset value on a counter or timer?
The target value set to activate the done (DN) bit.
What is the advantage to using latch and unlatch instructions instead of a relay?
Latch is retentive, the bit remains stored in the memory
True/false: A ladder logic branch can end in an input
False
What does the done (DN) bit indicate on a timer?
Timer has reached the preset value
Explain optical isolation in a PLC
The field device voltage and PLC circuitry voltage are equal, but not physically connected
