Chapter 1 electro mecha device part 4


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Chapter 1 electro mecha device part 4

  1. 1. D. Protection Circuit (Relays) <ul><li>There are 4 types of protection circuit </li></ul><ul><ul><li>Diode circuit </li></ul></ul><ul><ul><li>RC circuit </li></ul></ul><ul><ul><li>Zeners circuit </li></ul></ul><ul><ul><li>MOV circuit </li></ul></ul>
  2. 2. Different types of coil transient suppression
  3. 3. Coil transient suppression..cont. <ul><li>-When circuit complete (transistor forward </li></ul><ul><li>bias), current will flow into relay coil & not </li></ul><ul><li>through diode. </li></ul><ul><li>-relay coil energize, produce magnetic field from </li></ul><ul><li>i=0 to i=max. </li></ul><ul><li>-but if transistor is off, circuit is open, current </li></ul><ul><li>accumulate at relay coil need to discharge. </li></ul><ul><li>-Will go through diode, called freewheeling </li></ul><ul><li>diode. </li></ul><ul><li>-But if no protection device, it will go back </li></ul><ul><li>through relay coil and can cause arching (cause contact to </li></ul><ul><li>wear/oxidized). </li></ul><ul><li>-strength of the i=max will slowly decay its value until </li></ul><ul><li>i=0 </li></ul>
  4. 4. Pressure switch <ul><li>-Pressure is force exerted over a </li></ul><ul><li>surface divided by its area ; P=F/A </li></ul><ul><li>-Pressure switch is control switch that </li></ul><ul><li>detect amount of force & activates </li></ul><ul><li>electrical contact when the set amount </li></ul><ul><li>of force is reach. </li></ul><ul><li>-Application: </li></ul><ul><li>To control the air pressure in the tank </li></ul><ul><li>by turning the air compressor motor on </li></ul><ul><li>whatever the tank pressure falls below </li></ul><ul><li>the set value. </li></ul>NC Pressure switch NO Pressure switch
  5. 5. Pressure switch application <ul><li>-When switch is closed, current flows </li></ul><ul><li>through rung 1, motor will start </li></ul><ul><li>compress the air until system </li></ul><ul><li>pressure is reach. </li></ul><ul><li>-When system pressure is reach, the </li></ul><ul><li>NC contact will open & pump motor </li></ul><ul><li>is turn off. </li></ul><ul><li>-When pressure in the compressor </li></ul><ul><li>falls below the set point, pressure </li></ul><ul><li>switch in rung 1 will close and </li></ul><ul><li>restart the motor again. </li></ul><ul><li>-NO contact use to signal </li></ul><ul><li>overpressure condition. </li></ul><ul><li>-Alarm is sound when overpressure. </li></ul>
  6. 6. Example pressure switch. <ul><li>-Deflecting mechanism </li></ul><ul><li>that moves when a </li></ul><ul><li>force (pressure) is </li></ul><ul><li>applied </li></ul><ul><li>-Diaphragm switch use </li></ul><ul><li>for pressure less than </li></ul><ul><li>200psi. </li></ul>Diaphragm
  7. 7. Example pressure switch..cont. - Cylindrical device with several deep fold which expand or contract when pressure is applied. -The expanding bellow moves against spring mechanism which operate elect. contact when source pressure increase. -can use for pressure up to 500psi. Bellows
  8. 8. Example pressure switch..cont. - Move back & forth in a tight fitting chamber by pressure applied in a chamber. -Design for high pressure application of 10,000psi Piston
  9. 9. Limit Switch <ul><li>-require physical contact of the object </li></ul><ul><li>with the switch actuator. </li></ul><ul><li>-the mechanical motion physically </li></ul><ul><li>open or close a set of contact within </li></ul><ul><li>the limit switch </li></ul><ul><li>enclosure. </li></ul>NO limit switch NC limit switch
  10. 10. Reed Switch <ul><li>-electrical switch operated by an applied magnetic field. </li></ul><ul><li>- consists of pair of contact on ferrous metal reeds in a hermetically </li></ul><ul><li>(insulated or protected from outside influences) sealed glass </li></ul><ul><li>envelope . </li></ul><ul><li>-contact maybe normally open, closing when magnetic field is </li></ul><ul><li>present, or normally closed and opening when a magnetic field is </li></ul><ul><li>applied </li></ul><ul><li>-usage example-computer keyboards, petrol pump, automatic </li></ul><ul><li>dentist drill activation. </li></ul>
  11. 11. BREAK TIME ! <ul><li>Any Questions So far??? </li></ul><ul><li>Thank you see u on next story </li></ul>