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A timer or countdown timer is a type of clock that starts from a specified time duration and stops when reaching zero. A simple timer is an hourglass. Commonly, a timer would raise an alarm when it ends. It can be implemented as hardware or software. Stopwatches operate in the opposite direction, upwards from zero, measuring elapsed time since a given time instant. Time switches are timers that control an electric switch.
Mechanical timers use clockwork to measure time.Manual timers are typically set by turning a dial to the time interval desired, turning the dial stores energy in a mainspring to run the mechanism. They function similarly to a mechanical alarm clock, the energy in the mainspring causes a balance wheel to rotate back and forth. Each swing of the wheel releases the gear train to move forward by a small fixed amount, causing the dial to move steadily backward until it reaches zero when a lever arm strikes a bell. The mechanical kitchen timer was invented in 1926 called a fan fly that spins against air resistance, low-precision mechanical egg-timers are sometimes of this type.
The simplest and oldest type of mechanical timer is the hourglass - which is also known as "the glass of the hour" - in which a fixed amount of sand drains through a narrow opening from one chamber to another to measure a time interval.
Short-period bimetallic electromechanical timers use a thermal mechanism, with a metal finger made of strips of two metals with different rates of thermal expansion sandwiched together, steel and bronze are common. An electric current flowing through this finger causes heating of the metals, one side expands less than the other, and an electrical contact on the end of the finger moves away from or towards an electrical switch contact. The most common use of this type is in the "flasher" units that flash turn signals in automobiles, and sometimes in Christmas lights. This is a non-electronic type of multivibrator.
An electromechanical cam timer uses a small synchronous AC motor turning a cam against a comb of switch contacts. The AC motor is turned at an accurate rate by the alternating current, which power companies carefully regulate. Gears drive a shaft at the desired rate, and turn the cam. The most common application of this timer now is in washers, driers and dishwashers. This type of timer often has a friction clutch between the gear train and the cam, so that the cam can be turned to reset the time.
Electromechanical timers survive in these applications because mechanical switch contacts may still be less expensive than the semiconductor devices needed to control powerful lights, motors and heaters.
In the past, these electromechanical timers were often combined with electrical relays to create electro-mechanical controllers. Electromechanical timers reached a high state of development in the 1950s and 1960s because of their extensive use in aerospace and weapons systems. Programmable electromechanical timers controlled launch sequence events in early rockets and ballistic missiles. As digital electronics has progressed and dropped in price, electronic timers have become more advantageous.
Electronic timers are essentially quartz clocks with special electronics, which can achieve higher precision than mechanical timers. They have digital electronics, but may have an analog or digital display. Integrated circuits have made digital logic so inexpensive that an electronic timer is now less expensive than many mechanical and electromechanical timers. Individual timers are implemented as a simple single-chip computer system, similar to a watch and usually utilizing the same, mass-produced technology.
Nowadays, many timers are implemented in software. Modern controllers use a programmable logic controller (PLC) instead of a box full of electromechanical parts. The logic is usually designed as if it were relays, utilizing a special computer language called ladder logic. In PLCs, timers are usually simulated by the software built into the controller. Each timer is just an entry in a table maintained by the software.
Computer systems typically have at least one hardware timer. These are typically digital counters that either increment or decrement at a fixed frequency, which is often configurable, and which interrupt the processor when reaching zero. An alternative design uses a counter with a sufficiently large word size that it will not reach its overflow limit before the end of life of the system.
More sophisticated timers may have comparison logic to compare the timer value against a specific value set by software, which triggers some action when the timer value matches the preset value. This might be used, for example, to measure events or generate pulse-width modulated waveforms to control the speed of motors (using a class D digital electronic amplifier).
One specialist use of hardware timers in computer systems is as watchdog timers, which are designed to perform a hardware reset of the system if the software fails.
These types of timers are not devices nor parts of devices, they exist only as software. They rely on the accuracy of a clock generator usually built into a hardware device that runs the software.
Due to the increasing popularity of mobile phones, many timer apps have been developed that mimic the old mechanical timer, but which have also highly sophisticated functions. These apps are also easier to use, because they are available at once, without any need to purchase or carry separate devices. Timers can be software applications phones, smartwatches, or tablets. Some of these apps are countdown timers, stopwatch timers, etc. These timer apps can be used for tracking working or training time, motivating children to do tasks, replacing an hourglass-form egg timer in board games such as Boggle, or for the traditional purpose of tracking time when cooking.
Apps may be superior to hour glasses, or to mechanical timers. Hour glasses are not precise and clear, and they can jam. Mechanical timers lack the customization that applications support, such as sound volume adjustments for individual needs. Most applications will also offer selectable alarm sounds.
Some timer applications can help children to understand the concept of time, help them to finish tasks in time, and help them to get motivated.These applications are especially used with children with disabilities like ADHD, Down syndrome, etc., but everybody else can also benefit from them.
In digital logic and computing, a counter is a device which stores the number of times a particular event or process has occurred, often in relationship to a clock. The most common type is a sequential digital logic circuit with an input line called the clock and multiple output lines. The values on the output lines represent a number in the binary or BCD number system. Each pulse applied to the clock input increments or decrements the number in the counter.
In digital computers, an interrupt is a request for the processor to interrupt currently executing code, so that the event can be processed in a timely manner. If the request is accepted, the processor will suspend its current activities, save its state, and execute a function called an interrupt handler to deal with the event. This interruption is often temporary, allowing the software to resume normal activities after the interrupt handler finishes, although the interrupt could instead indicate a fatal error.
A logic gate is a device that performs a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic gate, one that has, for instance, zero rise time and unlimited fan-out, or it may refer to a non-ideal physical device.
A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis.
A relay is an electrically operated switch. It consists of a set of input terminals for a single or multiple control signals, and a set of operating contact terminals. The switch may have any number of contacts in multiple contact forms, such as make contacts, break contacts, or combinations thereof.
Digital electronics is a field of electronics involving the study of digital signals and the engineering of devices that use or produce them. This is in contrast to analog electronics which work primarily with analog signals. Despite the name, digital electronics designs includes important analog design considerations.
An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is embedded as part of a complete device often including electrical or electronic hardware and mechanical parts. Because an embedded system typically controls physical operations of the machine that it is embedded within, it often has real-time computing constraints. Embedded systems control many devices in common use. In 2009, it was estimated that ninety-eight percent of all microprocessors manufactured were used in embedded systems.
Ladder logic was originally a written method to document the design and construction of relay racks as used in manufacturing and process control. Each device in the relay rack would be represented by a symbol on the ladder diagram with connections between those devices shown. In addition, other items external to the relay rack such as pumps, heaters, and so forth would also be shown on the ladder diagram.
Automation describes a wide range of technologies that reduce human intervention in processes, mainly by predetermining decision criteria, subprocess relationships, and related actions, as well as embodying those predeterminations in machines. Automation has been achieved by various means including mechanical, hydraulic, pneumatic, electrical, electronic devices, and computers, usually in combination. Complicated systems, such as modern factories, airplanes, and ships typically use combinations of all of these techniques. The benefit of automation includes labor savings, reducing waste, savings in electricity costs, savings in material costs, and improvements to quality, accuracy, and precision.
A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial control systems which are used for controlling processes or machines. The control systems are designed via control engineering process.
A cam timer or drum sequencer is an electromechanical system for controlling a sequence of events automatically. It resembles a music box with movable pins, controlling electrical switches instead of musical notes.
A real-time clock (RTC) is an electronic device that measures the passage of time.
A stopwatch is a timepiece designed to measure the amount of time that elapses between its activation and deactivation.
A sprinkler system timer is an electrical device that is used to set an irrigation sprinkler system to come on automatically at a certain time. Irrigation timers first appeared in the early 1960s to control large-radius lawn sprinklers, which at the time usually contained their own electrically operated valve. These timers were large and cumbersome with numerous mechanical parts and were usually relegated to agricultural and commercial applications. Compact irrigation timers did not become commonplace until the 1970s when Lawn Genie introduced a mechanical timer which measured only ten by six inches and was four inches deep. This controller proved popular for many years, but was hard to reprogram and it did not operate valves in immediate succession unless each valve was set to run for an hour. Rain Bird later introduced the RC-7A to their Rain Clox line, which featured an "at a glance" electromechanical programming interface that proved very easy to operate, and offered the ability to omit stations from the program sequence without creating time gaps. This timer which became standard issue in many tract homes during the 1980s and proved to be remarkably durable in its construction, with many still operating today.
In engineering, hardware architecture refers to the identification of a system's physical components and their interrelationships. This description, often called a hardware design model, allows hardware designers to understand how their components fit into a system architecture and provides to software component designers important information needed for software development and integration. Clear definition of a hardware architecture allows the various traditional engineering disciplines to work more effectively together to develop and manufacture new machines, devices and components.
The following outline is provided as an overview of and topical guide to automation:
In electronics, an electronic switch is a switch controlled by an active electronic component or device. Without using moving parts, they are called solid state switches, which distinguishes them from mechanical switches.
A time switch is a device that operates an electric switch controlled by a timer.
The following outline is provided as an overview of and topical guide to electronics:
A photo-lab timer,photo interval timer, or darkroom timer is a timer used in photography for timing the process of projecting negatives to photosensitive paper with an enlarger, making photographic prints of them at any scale. It is a device which is attached to the photo lab enlarger to ensure that the duration of photo exposures on sensitive paper can be accurately timed. When the selected time has elapsed, the enlarger is switched off or an alarm is sounded, for the photographer to turn it off.