Relays have a wide range of applications, so we should have a basic understanding of devices such as relays. To deepen your understanding of relays, the following will introduce the classification of auxiliary relays and the differences between AC relays and DC relays.
1. auxiliary relay
Auxiliary relays are implemented in software, they can not receive the external input signals, also can not directly drive the external load, is an internal status mark, equivalent to the intermediate relay in the relay control system.
There are many auxiliary relays in the PLC, which cannot receive external input signals or directly drive the external load. Inside the PLC, it only plays the role of signal transmission and does not connect with the external PLC. It is an internal state sign, which is equivalent to the intermediate relay in the relay control system. Its normally open and normally closed contacts can be used for unlimited times when programming inside the PLC. The contact cannot drive the external load, and its coil is driven by the contacts of various soft components in the PLC, which can make the logical structure of the program clearer.
2. Auxiliary relay classification
1. General-purpose auxiliary relays
The universal auxiliary relay of the FX series PLC has no power-off protection function. In FX series PLC, except for the input relay and output relay components are in decimal system.
If the power supply is suddenly interrupted during PLC operation, the output relay and the universal auxiliary relay will all become OFF. If the power supply is switched on again, the OFF state will remain, except for the ON due to the external input signal.
2. Battery backup / latch auxiliary relay
Some control systems require an instantaneous power interruption for memory, where the battery backup / latch auxiliary relay can be used. Keep the contents of the image register in the RAM with a power outage, or save them in the EEPROM. They simply maintain the power off instantly during the first scan cycle after the PLC. To exploit their power-off memory function, circuits with memory functions can be employed.
3. Special auxiliary relay
Special auxiliary relays total 256 points, which are used to indicate some states of PLC, provide clock pulses and signs (e. g., carry, borrow sign), set the operation mode of PLC, or use for step control, no interruption, set whether the counter is added or subtract, etc
3. How to distinguish an AC relay from a DC relay
Choose the DC relay or the AC relay, many customers have a lot of confusion in their products. Customers often ask: my relay input is DC, output is AC; or my input is AC, output is DC; or DC to DC, AC to AC, ok. In the face of the problem of using AC relay or DC relay, it is necessary for us to popularize what is AC relay, what is DC relay, and then how to use it.
The most simple popular term: alternating current called AC relay, direct current called DC relay, AC relay working power supply for AC, DC relay working power supply for DC. The AC relay coil diameter is less than the thick turns, and the DC relay coil diameter has more fine turns. The AC relay core has a short circuit ring, no DC. The AC relay core is mostly E-shaped, and the DC core is cylindrical. AC coil because the core vortex and hysteresis loss will heat, so the coil has a skeleton to isolate the core from the coil, and the coil is short and thick short fat, so that the coil and the core heat dissipation.
DC coil is no skeleton, high and thin thin high type, so that the coil and core direct contact to facilitate heat dissipation. For the heating situation of the coil and the core, the AC electromagnetic system is heating parts, and there is a large gap between the coil, not the heat to the coil, and the coil shape is short and thick, facilitate the iron core cooling; DC magnetic system, the coil is a heating component, and the iron core cooling, and the coil shape is slender, facilitate the coil itself cooling.
Q: " If the coil is connected to the AC loop, can the contact be connected to the DC circuit?"This is OK, and conversely, if the coil is connected to the DC loop, its contact is connected to the AC loop. These two cases generally its cable Peugeot is different, its line number selection case is also different. But this circuit is easy to produce some induction voltage, which is easy to make misjudgment during measurement and maintenance.
Q: " How should the relay choose AC or DC?"The application scope of communication is more extensive, but the use of DC relay is relatively less. There are generally two kinds of DC relay application scope:
1 applied to the protection interlocking system, even in the case of factory AC power loss, can also trigger the protection circuit, of course, its contact must be DC system;
2 used in high power occasions, some occasions on the control of the electromagnetic force requirements can use the DC relay, because the same 220V but DC electromagnetic force is much larger, more beneficial to the control of the main loop. In automotive applications, we all use direct current to supply electricity, so we all use DC relays.