1. CHAPTER 10 Time Control Control With Timers Prepared by Adam Keeth for EE483 4-29-03

2. When Should One Use a Timer? Major function is to place information about elapsed time into a control circuit. Major function is to place information about elapsed time into a control circuit. Timers are not always the best way to control a circuit Timers are not always the best way to control a circuit Overshoot/Undershoot example Overshoot/Undershoot example Critical criteria (time, pressure, temperature, or position) Critical criteria (time, pressure, temperature, or position)

3. Timers and Time-Delay Relays Time Delay Relays Time Delay Relays Devices having a timing function after a timer coil has been energized. Then either NO or NC contacts activate. The only time function is the preset time. Devices having a timing function after a timer coil has been energized. Then either NO or NC contacts activate. The only time function is the preset time. Timers ( Much more versatile) Timers ( Much more versatile) The time function may start on one or many contacts at energizing, or at a preset time after energizing. The time function may start on one or many contacts at energizing, or at a preset time after energizing.

4. The Timer (continued) The timer opens or closes electrical circuits to selected operations according to a timed program. The timer opens or closes electrical circuits to selected operations according to a timed program. Timing function begins when the timer receives an electrical signal initiated through a manual switch or automatic sensor. Timing function begins when the timer receives an electrical signal initiated through a manual switch or automatic sensor. Preset time is user-defined. Preset time is user-defined.

5. Types of Timers 2 Primary Types: 2 Primary Types: Synchronous Motor Driven Synchronous Motor Driven Solid-State Type Solid-State Type Other Types: Other Types: Dashpot Dashpot Mechanical Mechanical Electrochemical Electrochemical Thermal Thermal Timing Functions: Timing Functions: ON delay Timing function after energizing. OFF delay Timing function after deenergizing.

6. Synchronous Motor Driven Timer Very Common in Industrial Applications: Very Common in Industrial Applications: Available in three types: Available in three types: Reset type Reset type Repeat-cycle type Repeat-cycle type Manual-set type Manual-set type Symbols Symbols

7. Reset Timers Use a clutch and a synchronous motor. Most reset timers have 3 contacts to provide output to the electrical circuit. Each contact has three conditions: Use a clutch and a synchronous motor. Most reset timers have 3 contacts to provide output to the electrical circuit. Each contact has three conditions: Reset – clutch and motor deenergized. Reset – clutch and motor deenergized. Timing – clutch energized. Timing – clutch energized. Timed Out – motor deenergized. Timed Out – motor deenergized. Sequence Chart – Figure 10-5

8. Repeat –Cycle Timers This type of timer is used to control several electrical circuits in a predetermined sequence. This type of timer is used to control several electrical circuits in a predetermined sequence. Adjustable cams on the motor shaft determine the point of closing and opening a switch during a revolution. In many cases, these cams are screwdriver-adjustable. Adjustable cams on the motor shaft determine the point of closing and opening a switch during a revolution. In many cases, these cams are screwdriver-adjustable. Activation time and duration time are adjustable. Activation time and duration time are adjustable. Most include external calibrated discs to observe the progress of the timer (Figure 10-9). Most include external calibrated discs to observe the progress of the timer (Figure 10-9).

9. Manual-Set Timers This type requires manual operation to activate the timer. This type requires manual operation to activate the timer. Timer runs and stops after a selected time. Timer runs and stops after a selected time. Figure 10-10A&B

10. Solid State Timers Microprocessor-type timers are the most versatile timers available. Microprocessor-type timers are the most versatile timers available. Many incorporate keypad input and digital/LCD readout. Many incorporate keypad input and digital/LCD readout. Very accurate Very accurate 100% accurate for count operations. 100% accurate for count operations. Within 50 ms (or 0.5%) accurate for timing operations. Within 50 ms (or 0.5%) accurate for timing operations. Can retain data for many years. Can retain data for many years. Most are repeat-cycle capable. Most are repeat-cycle capable.