air, liquid.Ī pressure switch can be called a pressure relay. Pressure switch Pressure switch with NO contact The contact is driven by pressure, e.g. Below is an example on a pressure switch: Symbol Therefore, with contacts controlled other than electrically, their drive is drawn. The wiring diagram will not draw the pipeline in which the pressure switch is installed, only its contact. Drives with contacts can also be drawn as one symbol, e.g. a phase control sensor can be drawn on one page and its auxiliary contact on the next page. This also applies to devices with special functions, e.g. For example, solenoids may be drawn on a different page of the schematic than contacts. In wiring diagrams, contact drives can be drawn in several ways. When analyzing the wiring diagram, we should first pay attention to the actuator that triggers the contact and analyze its use in the diagram. through-hole, self-reversing and other functional symbols, rather rarely used. There are several other contact symbols on the schematic diagrams, e.g. It can be used, for example, to confirm motor operation by transmitting a signal via this contact to a lamp or PLC It is used in a control system when there is a need to transmit information with a small delay after the main/normal contacts are switched on. Can be used for protection in control systems.ĭelay NO contact – This type of contact closes with a delay compared to “normal” contacts connected to the same actuator. switching on the motor by the main contacts. It is used in a control system when there is a need to transmit information faster than e.g. Actuating the drive switches the contact from 11.12 to 11.14Ĭontactor main contact – Contactor power contact Contactor operating contact Īdvance NO contact – This type of contact closes in advance of “normal” contacts connected to the same actuator. NCNO contact – general symbol for a changeover contact c/o (close/open) contact. Activation of the drive opens the contact and there is no transition between terminals 11 and 12 NC contact – general symbol for normally closed contact opening contact. Actuating the actuator (e.g., pushbutton, solenoid) short-circuits the contact and there is a transition between terminals 13 and 14. NO contact – general symbol for normally open contact closing contact. Electrical symbols – Contact types Symbol In this article, I will introduce other types of contact control. In lessons #2 and #3, electromagnetic drives – coils – have been described. However, shorting or opening the contacts can be controlled in many ways – thanks to actuators. We know from previous lesson #2 that electrical contacts can be normally open (NO) and normally closed (NC) or changeover (NCNO). In this lesson, I will provide a summary of contact symbols along with their drives. There are many other devices in which the contacts are switched mechanically, inductively, pneumatically or hydraulically. In the previous two lessons, I wrote about relays and contactors, where the electrical contacts were switched electromagnetically.
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