Contacts and Coils



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Contacts stand between power and Coils, asking questions.  If the answer to the question is true, then power is allowed to flow through the contact, if not the path is blocked.

List of typical Contacts:

Normally Open asks if a bit is = 1

Normally Closed asks if a bit is = 0

Rising Edge asks if a bit just turned from 0 to 1

Falling Edge asks if a bit just turned from 1 to 0

Less Than asks if Value A is less than Value B.

Greater Than asks if Value A is greater than Value B

Less Than or Equal asks if Value A is less than or equal to Value B.

Greater Than or Equal asks if Value A is greater than or equal to Value B.

Equal asks if Value A is equal to Value B.

Not Equal asks if Value A is not equal to Value B.

Contacts placed side by side to form AND statements.

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Example: Coil gets power if: Contact_A AND Contact_B

Contacts placed one on top of each other to form OR statements.

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Example: Coil gets power if: Contact_A OR Contact_B

AND and OR statements may be combined to form complex expressions.

 

Example: Coil gets power if: Contact_A AND (Contact_B OR Contact_C)

Coils

Each Coil is tied to a specific Bit of data.  Here are the standard Coil Types and what they to the specified Bit.

  • Out: If the Coil is powered, the bit is assigned a 1.  If not it’s assigned a 0.coilcontact4
  • Set: If the Coil is powered, the bit is assigned a 1.  If not, the value remains whatever it was.
  • Reset: If a Coil is powered, the bit is assigned a 0.  If not, the value remains whatever it was.
Contacts and coils are often associated with the physical Inputs & Outputs on the PLC. 
If  a contact is tied to an Input, then when the power at the input changes it’s contact value in the Ladder Logic will Change.  If a coil is tied to an output and the coil changes it’s value, then the voltage (or contact state) at the output will change.

Functions:  vBuilder offers many functions including Calculator, Counter, Drum, Filter and many more.  These functions can be placed anywhere a coil can be placed.  Where the function is powered it’s operation occurs.

For more information, check out the vBuilder Manual.  It explains every tool and goes through examples using both Ladder Logic and Flow Charts.