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Problem in dalher connection QUESTION: Contactors in a Dahlander connection are controlled by a PLC. Very often contactors are welding after a speed changeover commands. No transition times are parameterized into the PLC program. Contactors are electrically interlocked however. ANSWER: Enhanced by unfavorable configurations of line frequency and residual magnetic field of rotor, transient reactions inside the motor occur during a changeover of motor speeds. As a result current peaks arise higher than current peaks during ordinary DOL starting. In the worst case the making capacity of contactors is exceeded with contact welding as a consequence.In order to allow the residual magnetic rotor field in to decay, a transition time of at least 50 ms has to be allowed before the line voltage is re-connected during speed changeovers .....

Errors and their Adjustments in 1Φ energy meter Energy meters should give correct readings over a period of several years under normal use conditions. Some of the common errors in energy meter and their remedial measures are discussed below. 1.        Phase Error: It is necessary that the energy meter should give correct reading on all power factors, which is only possible when the field setup by shunt magnet lags behind the applied voltage by 90 o . But the flux due to shunt magnet does not lag behind the applied voltage exactly by 90 o because of winding resistance and iron losses. Adjustment: The flux in the shunt magnet can be made to lag behind the supply voltage by exactly 90 o by adjusting the position of shading band (or shading ring or shading coil) placed round the lower part of the control limb of the shunt magnet. This adjustment is known as lag adjustment or power factor adjustment (or power factor compensator ). 2.     ...

Multiple Pedals or Effects in the same box - switching.

In an evident attempt to retain its market-dominating position in the fiercely competitive smartphone and tablet arena, tech giant Apple is reportedly preparing for a busy close to the ongoing year, with the launch of new iPhone and iPad models. According to unidentified sources aware of the proceedings at Apple, a new iPhone model - and probably even a budget iPhone aimed at smartphone users in developing countries - will be unveiled by the company at a September 10 event. Along with hinting at the possible introduction of a new iPhone model at the September event, two sources have also revealed that Apple will also launch new iPad models in the coming months. These models will include an iPad with a sleeker body design, as well as an iPad Mini with a high-resolution screen. The speculated update of the iPhone and iPad models by Apple will give the company the ability to unveil a refreshed lineup of its best-selling products to consumers, ahead of the holiday shopping season this ye...

Want to avoid the problem of carrying three different flashlights to perform a test? Why don’t you try integrating Ultra Violet, Infra Red and visible light together in one flashlight? Read on to know more about this. The multi-tasking flashlight is basically composed of a metallic case, a switch, cables and connections, four 9V batteries and three different LED heads that provide the desired light beam. For the construction of this flashlight, LedEngin’s LZ4-40 is recommended. This comes with a very wide wavelength that includes infra red and ultra violet light. Distinct visible light color temperature can also be found The first step is to build the body of the flashlight, using an aluminum tube. Next come the drilling and cutting for switches and covers. Once the body is finished, the work on the constant current driver should be completed, adding the proper terminals for the batteries and the base for the LED heads.  Once all the power source wiring is completed and insulated w...

Multiple Switching Operation is a system where the street light can be energized and de-energized (switch ON and OFF) from multiple location by simply a push button switch. Figure below (A)  illustrate the layout of the street lights (L1,L2,L3…Ln) which are installed in the street of camp M. By pressing any one of the push button switches P1,P2,P3,P4, and P5 installed in buildings A,B,C,D, and E respectively, one can switch On and OFF the street lights. Multiple Switching Operation applied to lights in a camp Control Circuit Operation Figure below (B) illustrates the control circuit of a multiple switching operation. Encircled A and B maybe the power made of relay or contactors. Encircled C is the power contactor that will energized the street lights (L1,L2,L3…Ln) directly from the source. Pressing any one of the five push button switches (P1,P2,P3,P4 and P5) will energized contactor A. For example, pressing the push button switch P3 which is at the Administrator building will cause th...

Types of Timers in PLC | OFF Delay Timer (TOF)   PLC Timers are generally used for delaying an event from taking place, or to delay a device from shutting off either on an on transition or an off transition.   There are three types of PLC timers:   The Timer ON delay (TON), Timer Off delay (TOF), and the Retentative Timer On delay (RTO). By default, timers are stored in the T4 Data file, however other time files can be created. A timer consists of the following components:   Preset word (PRE), Accumulate word (ACC), Done bit (DN), Timer Timing bit (TT), and Enable bit (EN).   For Timers, the Enable bit follows the rung condition. The entire timer is addressed by it's element (example: T4:0) Pieces of the timer can be used in logic however such as the DN bit on an XIC (T4:0/DN), or the Accumulated value in a MOV statement (T4:0.ACC) PLC Timer Off Delay (TOF)   The Off Delay Timer is generally used to delay an event from shutting off.   Image a lube sy...