![]() The circuit is meant purely to illustrate the operation of the TDRs discussed in this article additional circuitry is required to complete a functioning crusher circuit. 3) illustrates a simple circuit for a crusher and its feeder conveyor. In the three examples below, learn how you can use TDRs effectively to manage processes in various manufacturing facilities.Ĭrusher and conveyor line - Figure 3 (click here to see Fig. Let’s put our basic TDR knowledge to practical use. The only means to interrupt the operation is to remove voltage. The TDR is reset at this time, ready for another cycle. Only at time-out will the contacts transfer. While timing, the control input can be left open, closed, or opened and closed in each case, timing continues, and the contacts remain closed. On closure of the control input, the contacts transfer and timing begins. Repeat cycle - Operation is similar to the flasher, but the timing cycles are independently adjustable.Ī single-shot TDR has voltage and control inputs similar to the off-delay TDR. On and off cycle times are the same lengths. Timing action is halted by removing voltage from the coil. Power must be removed and reapplied to restart.įlasher - When voltage is applied, the contacts energize and de-energize alternately. At the end of the timing interval, the contacts transfer. Interval-on-operate - When voltage is applied to the coil, contacts transfer, and timing begins. The state of relay contacts is always shown with voltage removed.īeyond the few types of timers already mentioned in this article, additional types are available, such as: Often, a note is made near the relay symbol to denote the operating condition. Other types of TDRs simply use the same contact symbols as those for relays. In fact, they are the only TDRs for which special contact symbols have been assigned. ![]() There are special contact symbols for the on-delay and off-delay timers. They have capacitors to keep contacts closed even if the timer loses power. In addition, true off-delay timers provide this functionality (keeping contacts closed) after input voltage is lost. Removing voltage prior to time-out resets the timing and opens the contacts. Closing the control input prior to time-out causes timing to reset. Opening the control input causes timing to begin, and the contacts remain closed. Closing the control input (SW) causes the contacts to transfer (click here to see Fig. When using an off-delay timer, nothing happens when voltage is applied. If voltage is removed before time-out, the time delay resets (click here to see Fig. When the time has expired, the contacts close - and remain closed until voltage is removed from the coil. With an on-delay timer, timing begins when voltage is applied. Let’s take a closer look at a few of the more common types of TDRs. In addition, newer multifunction IEC-style timers allow for reduced inventories. Costing little more than single-function devices, these TDRs also have wide control voltage ranges. Today, many TDRs are also available with multiple timing ranges and functions. These devices are still available and are typically used in applications where the timing needs to be locked in. Traditionally, TDRs were available only as single-function, single-time-range devices. Some TDRs have solid-state outputs instead of relay outputs. Electronic, starter-mounted TDRs are also available. In this application, energizing the motor starter causes the timing function to begin contacts within the device operate when timing is complete. For instance, a TDR can be fixed on a motor starter. However, they are also available in a range of other forms, including base-mounted devices and direct IEC DIN-mounted controls. TDRs are available as plug-in devices, much like plug-in control relays. However, some TDRs postpone closing of the contacts after voltage is applied while others close the contacts - and then reopen them after a delay. In a variety of applications, it’s desirable to have the operation of the contacts delayed following application or removal of voltage. In a standard control relay, contacts close immediately when voltage is applied to the coil, and open immediately when voltage is removed. They have a variety of features and operating characteristics, such as compactness, economy, simplicity, and ease-of-use. Additionally, they play an important role for targeted logic needs, such as in a small panel or in sub-panels. Providing time-delayed switching to start a motor, control a load, or affect a process, TDRs are typically used in industrial applications and OEM equipment. Adjusting the delay time is often as simple as turning a knob. No matter what the application is, when a definite-purpose solution is required, time delay relays (TDRs) can provide simple, reliable, and economical control.
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