TOF: Off Delay Timer

Introduction

The TOF off delay timer function block turns an output off after a delay.

Syntax

The TOF Function Block has this syntax:

TOF(
        IN:=Expression,
        PT:=Expression,
        Q=>Variable-Reference,
        ET=>Variable-Reference );

Note: All parameters are optional.

Parameters

Parameter	Type	Direction	Description
IN	BOOL	Input	A rising edge starts the timer.
PT	TIME	Input	The duration of timer.
Q	BOOL	Output	Set to false after delay PT.
ET	TIME	Output	The elapsed time of the timer.

Remarks

The TOF Function Block uses this logic:

If the input IN is TRUE:
- Output Q will be TRUE.
- Output ET will be T#0s.
If the input IN transitions to FALSE, output ET increases until it reaches PT.
When output ET reaches PT, output Q will be set to FALSE.

These timing diagrams show the relationship of the TOF inputs and outputs:

       +---+        +---+ +-----
  IN   |   |        |   | |
     --+   +--------+   +-+

       +--------+   +------------
  Q    |        |   |     
     --+        +---+       

                +---+
               /    |
              /     |
  ET         /      |     +
            /       |    /|
     ------+        +---+ +---

Standards Compliance

IEC 61131-3 Second Edition: Table 37.3.

IEC 61131-3 Third Edition: Table 46.3a.

Further Information

TON Function Block

To learn about a function block that turns an output on after a delay.

Standard Function Blocks

To learn about other standard function blocks.

Elementary Data Types

To learn about the different types supported by Fernhill SCADA.

Common Elements

To learn about other IEC 61131-3 Common Elements.

Glossary

For the meaning of terms used in Fernhill SCADA.