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Labs - Safety first. Safety First! Powerful rotating machinery and high voltage! Accidents may occur, we must take precautions Know basic first aid Concentrate fully on the task, at all times Watch your fellow student and warn him/her if necessary

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Labs safety first
Labs - Safety first

  • Safety First!

  • Powerful rotating machinery and high voltage!

  • Accidents may occur, we must take precautions

  • Know basic first aid

  • Concentrate fully on the task, at all times

  • Watch your fellow student and warn him/her if necessary

  • You may be required to sign regulations for working in the lab

Lecture 1


Labs safety first1
Labs – Safety first

  • Rotating machinery

    • Long hair – roll up hair under cap

    • No loose sleeves on shirt and jackets

    • Wearing tie or scarf in the labs is strictly forbidden

    • Touching moving parts is strictly forbidden

    • Never lean over running machinery

    • Stand back whenever possible

    • Do not touch anything unless necessary and stationary

Lecture 1


Labs safety first2
Labs – Safety first

  • High voltage is dangerous

    • Make connections before turning the ”ON” switch

    • Turn swith ”OFF” before disconnecting equipment

    • As a general rule, always check voltage before you touch live equipment parts, even if you ”know” that power is turned OFF

    • Use insulated voltage, current and temperature probes

    • Never touch equipment parts under voltage (live parts)

    • Wearing rubber soled shoes is always an advantage

    • Never touch or lean onto metal machinery parts while making measurements with probes – then you may create a current path to earth

    • Wearing metal finger rings may be risky

Lecture 1


Labs safety first3
Labs – Safety first

  • Low voltage is potentially harmful

    • In general you follow the same rules as for high voltage.

    • Wearing finger rings is risky

    • Example: A guy is disconnecting his 12 V car battery, using a steel wrench. He first disconnects the positive terminal, and his finger ring suddenly short circuits the wrench to the car chassis. The finger is burnt to the bone.

  • Examples of incidents with a 24 V DC /230 V AC power inverter

    • In the half bridge inverter the transistor switches are mounted on large cooling fins, not insulated from transistor collectors. You have moist hands and take a firm grip with the left hand on one and the right hand on the other cooling fin to compare temperature. Then you have 2 x 24 V between moist hands. The electric shock may be harmful – it is certainly painful, and you get dizzy and are breathing heavily: I still remember I did this in 1968: Have respect also for 24 V DC.

    • You touch a 230 V part of the inverter with one hand and the chassis/earth with the other hand

Lecture 1


Labs safety first4
Labs – Safety first

Working with inductors

  • Inductors give a voltage surge when current is suddenly interrupted

  • The voltage limiting mechanism is usually arcing through winding insulation breakdown

  • Typical surge voltage is 2 – 5 kV

  • Therefore: Swith circuit ”OFF” before disconnecting an inductor

  • If you are measuring ohmic resistance, short circuit the inductor before disconnecting instrument probes

Lecture 1


Labs safety first5
Labs – Safety first

Working with capacitors

  • Good capacitors keep their voltage for hours after being disconnected

  • Disconnect capacitors only after equipment is powered ”OFF” and capacitors have had time to discharge

  • Sometimes a meg-ohm discharge resistor is connected across capacitor terminals

Lecture 1


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