1. PLC Timers
MECH 1500
Two classes of timers:
Retentive
Non-Retentive

2. PLC Timers
MECH 1500
Retentive – accumulates total time instruction has been energized and retains it when it de-energizes, meaning that it resumes timing when it is energized again.
Application: Pumping applications. If a pump stops in the middle of filling, it can pick back up where it started.

3. PLC Timers
MECH 1500
Non-Retentive – accumulates time when energized, but resets whenever it is de-energized.
Application: Machine start ups

4. PLC Timers
MECH 1500
Step 7 Timers location in the editor program elements window in the System Function Blocks folder:

5. On Delay Timers
MECH 1500
On-Delay Timer – Energizes its contacts after it has been turned on for an amount of time equal to its preset value.
It stays on until it is de-energized, resetting the timer.
Non-Retentive
Example: Allowing an oven to reach a certain temperature before starting production.

6. On Delay Timers
MECH 1500
Preset Time Value– The amount of time the instruction must be energized before the timer coil is energized.
Siemens allows time resolutions of 10, 1.0, 0.1 and 0.01 seconds to be programmed

7. On Delay Timers
MECH 1500
S5T#_xh_ym_zs_xxms

8. On Delay Timers Timer contacts correspond to the Timer number
MECH 1500
Timer contacts correspond to the Timer number

9. On Delay Timers
MECH 1500
Example

10. OFF Delay Timers
MECH 1500
Off-Delay Timers – Energizes its contacts as soon as the instruction is energized. When the timer coil is de-energized, the contacts remain energized and the timer starts timing.

11. OFF Delay Timers
MECH 1500
Same principles apply to Off-Delay Timers as the On-Delay timers for time increments and contactors

12. Off Delay Timers
MECH 1500
Example