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Youblob (generated from this blueprint's notebook) · CC0
The Time-Delay Relay: Switching a Set Time Later
Many control jobs need a pause: start the motor, wait until it is up to speed, then load it; stop the burner, then run the fan a little longer to clear the heat; light the stairway, and switch it off a few minutes later. The time-delay relay does it. An on-delay closes its contact a set time after it is energised; an off-delay keeps its contact closed a set time after it is de-energised.
The earliest timed their delay with a dashpot — a piston pushing air or oil through a small adjustable hole — or with a bimetal warmed by a heater. Electronic relays charge a capacitor through a resistor and switch when it reaches a threshold.
This rung works out an RC delay and why capacitor tolerance and leakage limit it, draws on- and off-delay timing, and builds an on-delay relay with a 555 timer.
初学者
About 3 hours
说明
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1
The RC delay and its limits
The RC delay and its limits
正在加载 Jupyter 笔记本…
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Build a 555 on-delay relay
Build a 555 on-delay relay
On a breadboard wire a 555 as a monostable from a 9–12 V supply: pins 4 and 8 to the supply, pin 1 to 0 V, a resistor R from the supply to pins 6 and 7 joined, a capacitor C from pins 6 and 7 to 0 V, 10 nF from pin 5 to 0 V, and pin 2 (trigger) held high through 10 kΩ with a push button to 0 V.
Pin 3 goes high for 1.1 RC after the button is pressed. Drive an NPN transistor from pin 3 through 1 kΩ, with the relay coil between the supply and the collector and a diode across the coil, reversed, to catch the coil's kick. Wire an LED through the relay's contact.
Time the relay with a stopwatch for three values of R. Plot delay against R: a straight line whose slope is 1.1 C. Swap in a second capacitor of the same marked value and watch the delay change — its tolerance.
此步骤所需材料：
NE555 定时器集成电路1 个
NPN 晶体管1 个
SPDT 继电器1 个
二极管1 个
电容套件1 个
电阻套件1 个
按钮1 个
5 毫米 LED1 个
面包板1 个
跳线1 个
时间继电器1 个所需工具：
直流电源
万用表
秒表3
3
The relay it times
The relay it times
A time-delay relay is a relay with a clock in front of it. The embedded blueprint shows the electromagnetic relay it drives.
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4
A timer that times wrong
A timer that times wrong
Time-delay relay faults.
Flow
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5
Context and honest limits
Context and honest limits
Pneumatic dashpot timers, thermal timers and motor-driven timers served machine and process control for decades; the 555 timer IC, introduced in 1972, made cheap electronic delays universal, and programmable controllers now provide timers in software.
**Honest limits.** An RC delay drifts with temperature and with the capacitor's age. For accurate long delays use a crystal-timed or counting timer. A relay switching mains loads must be wired and enclosed by someone qualified; the bench build stays at low voltage.
材料
11- 占位符
- 1 个占位符
- 1 个占位符
- 1 个占位符
- 1 个占位符
- 1 个占位符
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