Short description

The edge of an input pulse triggers a configurable time. The output is reset when this time has expired. An off warning can be output prior to the expiration of this time.

Connection	Description
Input Trg	You trigger the time (off-delay) for the stairway switch with a signal at input Trg (Trigger).
Parameter	T : The output is reset (1 to 0 transition) when the off-delay time T has expired. T! : determines the triggering time for the prewarning. T!L : determines the length of the prewarning time. Retentivity set (on) = the status is retentive in memory.
Output Q	Q is reset after the time T has expired. A warning signal can be output before this time has expired.

Parameters T, T_! and T_!L

The off-delay time T, the prewarning time T_! and the prewarning period T_!L can be provided by the actual value of another already-programmed function:

• Analog comparator: Ax - Ay

• Analog threshold trigger: Ax

• Analog amplifier: Ax

• Analog multiplexer: AQ

• Analog ramp: AQ

• Mathematic instruction: AQ

• PI controller: AQ

• Up/Down counter: Cnt

For the 0BA7 devices, you can additionally use the actual values of the following already-programmed functions:

• On-delay: Ta

• Off-delay: Ta

• On-/off-delay: Ta

• Retentive on-delay: Ta

• Wiping relay(pulse output): Ta

• Edge triggered wiping relay: Ta

• Asynchronous pulse generator: Ta

• Stairway light switch: Ta

• Multiple function switch: Ta

• Stopwatch: AQ

• Analog filter: AQ

• Average value: AQ

• Max/Min: AQ

• Thresholder trigger: Fre

You select the required function by the block number.

Timing diagram

The prewarning time is set to 15 s. The T! and T!L parameters thus become obsolete.

Changing the time base

You can change the prewarning time base and the period.

Time base T	Prewarning time	Prewarning period
Seconds *	750 ms	50 ms
Minutes	15 s	1 s
Hours	15 min	1 min
* makes sense only for programs with a cycle time of < 25 ms

Description of the function

Output Q is set to 1 with a 0 to 1 signal transition at input Trg. The 1 to 0 transition at input Trg triggers the current time and output Q remains set.

Output Q is reset to 0 when Ta reaches the time T. Before the off delay time (T - T_!) has expired, you can output a prewarning that resets Q for the duration of the off prewarning time T_!L.

Ta is retriggered (optional) at the next high/low transition at input Trg and if Ta is expiring.

Scan cycle time

For information on how to determine the scan cycle time of a LOGO!, refer to the appendix of the LOGO! manual.

Special Functions Overview