Time delay relays and solid state timers use solid state electronic devices to provide a time delay. They may have displays, pots or other means of operator interface and electromechanical or solid state outputs. The number of time ranges on relays and timers are single or multiple. Single time ranges may be fixed or programmable. Timers with multiple time ranges can be programmed for multiple ranges. A minimum and maximum time setting must also be specified. Some relays and timers have field selectable time ranges. Time delay relays and solid state timers can have many timer functions or modes of operation, including ON-delay, OFF-delay, one shot and interval.

ON-delay timers and OFF-delay timers are two common types of time delay relays and solid state timers. An ON-delay timer can also be called Delay on Make, Delay on Operate, Operate Delay, Prepurge Delay and Delay on Energization. The time delay begins after application of power. At the end of the time delay the contacts open or close. If the contact is normally open (NO) the load energizes at the end of the time delay. If the contact is normally closed (NC) the load de-energizes after the time delay. Removing power resets the time delay and output. OFF-delay timers are sometimes called Delay on Break, Release Delay, Delay on Release, Postpurge Delay and Delay on De-Energization. The timer contacts open or close immediately after power is removed. The preset time delay must elapse before the contacts return to normal position and the load is de-energized. Power must be applied before and during timing. Re-closing the control switch during the timing resets the time delay. Most reset on loss of power. 

One shot timers are time delay relays and solid state timers that are also called a One Shot Relay, Single Shot, Single Shot Interval, Single Pulse, Latching Relay, Latching Off Delay and Latching Delay on De-Energization. Contacts change position immediately upon application of power and remain in changed position for the preset time delay. After the time delay, the contacts return to their normal position. Power must be applied before and during timing. Reset occurs when the time delay is completed and the control switch is opened.  

Interval timers are time delay relays and solid state timers that are also called Interval On, On Interval, Pulse Shaping, Bypass Timing, Interval Delay and Delay on Energization with Instantaneous Transfer. Time delay begins when power is applied. The output is energized during time delay and de-energizes at the end of the time delay, and it remains de-energized until power is removed. Removing power resets the time delay and output.  A recycle timer is also called Recycle Timing, Duty Cycling, Cycle, Repeat Cycle, Delay on Operate and on Release, On/Off Dual Delay, Flasher and Dual-Delay Energization. Timing function starts with closing of control switch. The load alternately turns ON and OFF at regular intervals until power is removed. Removing power resets the time delay. A time indicator records and displays elapsed time but performs no output function.  Some timers can be programmed to function as a counter as well as timing functions. Time delay relays and solid-state timers are either single function or multi-function devices.

Common user interface specifications for time delay relays and solid state timers include input controls and displays. Input controls include none, analog, or digital.  Display types include none, analog meters or simple visual indicators, and digital numerical displays. Output specifications to consider when selecting time delay relays and solid state timers include the switch type, number of contacts, contact configuration, and pole and throw specifications. Mountings and power supplies also need to be specified. Operating temperature is an important environmental parameter to consider when selecting time delay relays and solid state timers.

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Bowden's Hobby Circuits 120VAC Lamp Chaser Using Solid State Relays Power-On Time Delay Relay Circuit Power-Off Time Delay Relay Circuit

555 Timer/Oscillator Tutorial is and how to properly use it by itself or in combination with other solid state devices without the requirement of an engineering degree. See University of Guelph Information

ABB SSAC Time Delay Relays: Plug-in Package - Octal or 11 Pin... Time Delay Relay Plug-in Time Delay Relay Universal Time Delay Relay AC Time Delay Relay DC Time Delay Relay Knob Adjust Time Delay Relay Switch See ABB SSAC, Inc. Information

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