1. What are the two basic classifications of timers? 2. Explain the operation of an on-delay relay. 3. Explain the operation of an off-delay relay. 4. What are instantaneous contacts? 5. How are pneumatic timers adjusted? 6. Name two methods used by electronic timers to obtain their time base.
Answer (1)
What are the two basic classifications of timers?
The two basic classifications of timers are analog timers and digital timers . Analog timers generally use mechanical means or pneumatic systems to measure time, while digital timers use electronic methods to count and display time intervals.
Explain the operation of an on-delay relay.
An on-delay relay is used to delay the activation of an electrical circuit after a specified amount of time. When the control input to the relay is activated, the relay does not immediately close its contacts. Instead, it waits for the preset time interval. After this delay, the contacts close, allowing current to flow through the circuit. This type of relay is often used to sequence operations in industrial applications where time delays are necessary.
Explain the operation of an off-delay relay.
An off-delay relay operates oppositely to an on-delay relay. When the control input is deactivated, the relay remains energized for a preset time interval before its contacts open. This allows the connected circuit to continue operating for the duration of the time delay after the control signal is removed. Off-delay relays are useful in applications where a device needs to run for extra time after being switched off, like cooling fans.
What are instantaneous contacts?
Instantaneous contacts are relay contacts that operate without any intentional delay as soon as the relay coil is energized or de-energized. They immediately change state (either open or close) in response to the control input. This type of contact is used when quick action is necessary without any delay.
How are pneumatic timers adjusted?
Pneumatic timers are adjusted by changing the flow of air through a restrictor. The timing is controlled by regulating the air pressure or the size of the orifice through which the air flows. By adjusting these parameters, the delay time can be lengthened or shortened, allowing precise control of the timing operation.
Name two methods used by electronic timers to obtain their time base.
Electronic timers often use either of the following two methods to obtain their time base:
Quartz Crystal Oscillator: A quartz crystal oscillator provides a very precise and stable frequency, which is used as a reference time base.
RC (Resistor-Capacitor) Networks: RC networks are used as time constants to produce timing functions. They are less precise than quartz oscillators but are suitable for applications where high precision is not essential.
