Electromechanical timers are used to start or stop a machine or other device at preset or delayed intervals. They consist of both electrical and mechanical components, and often feature an electric motor that drives one or more gears. They typically accept electric or electronic inputs to operate a mechanical output such as rotating wheels or knobs.
How Electromechanical Timers Work
Some electromechanical timers, such as the turn signals or flashers in automobiles, rely upon the thermal expansion of metal fingers. When electric current flows through and heats these bimetallic fingers, one side expands and moves away from the switch contact. In most industrial and factory applications, however, electromechanical timers are driven by a synchronous motor that turns the cam through the switch contacts. Often, there is a friction-clutch between the cam and the gear train.
The GlobalSpec SpecSearch database provides detailed product information about many different types of electromechanical timers. These are five common types.
Delay on timers open or close a switch’s contacts after an input signal is received and a predetermined amount of time has passed. If the switch’s contacts are normally open (NO), the load is energized. If the contacts are normally closed (NC), however, then the load is de-energized.
Delay off timers begin their timing function when the power supply is interrupted. In other words, when a predetermined amount of time has elapsed, the output relay contacts release. Often, this capability is called delay on release, delay on break, or release delay.
One shot timers or pulse formers have contacts that change position when power is applied and remain changed for a set period. After this time period has passed, the contacts return to their normal position.
Internal delay timers are energized immediately when power is supplied or the switch input is closed. They are the opposite of delay on timers because they turn off at the end of the period. Some suppliers call interval delays a delay pulse timer.
Recycle timers or percentage timers start their cycling function when the control switch closes. As long as the control switch remains closed, the load continues to turn ON and OFF at regular intervals. This cycling stops when the control switch is open.
Other types of electromechanical timers in the GlobalSpec SpecSearch database include position indicators, delay cycles, and preset timers.
Product Specifications and Features
Electromechanical timers can be setup or programmed to perform one or more functions. They differ in terms of accuracy and repeatability, and have both minimum and maximum time intervals. Although some products can be configured for only a single time range, others can be programmed for multiple ranges or are field-selectable.
Electromechanical timers may accept a voltage, current, frequency, or pulse as an input, and can send serial, digital, or switch outputs.
Programming options vary, and often include knobs, dials, keypads, and pushbuttons.
In terms of features then, electromechanical timers may be rated as explosion proof or include audible alarms and visual signals.
Typically, electromechanical timers are used in factories and other industrial settings. For example, they may cause a valve to open and remain open for a specified period of time, or cause a mixer to turn-on and remain running upon receiving a signal that more mix has been added.