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Homework Help: I need the solution for the 3 important problems

  1. Jul 3, 2011 #1
    Question 1:
    A pressure gauge has accuracy equal +/-2% of full scale. The gauge range is from 0 to 100 kg/cm2. When the gauge indicate 50 kg/cm2 What is the tolerance of this indication?

    a) +/- 2 kg/cm2
    b) +/- 10 kg/cm2
    c) +/- 1 kg/cm2

    Question 2:
    An instrument system consists of pressure transducer with a range of 0 to 4 bar and a corresponding output of 0 to 10 mV. The output is connected to an electronic processor which converts the output into a current in the range 4 to 20 mA, and an analogue meter which indicates the measured pressure.
    If the output of the signal processor is 12 mA. Deduce the indicated pressure?

    a) 2 bar
    b) 5 bar
    c) 2.5 bar

    Question 3:
    What is the minimum motor power capacity required to drive a water pump to raise water from sea level to a hill of 1000/9.8 m height AMSL to get a flow rate of 1000 cu m/sec. Ignoring pipe losses. If the motor is to be fed by a 11KV feed, using a 1.1 safety factor, what is the size of the used cable using the following details.

    mm2 ------- Ampere
    16 ------------110
    25 ------------140

    a) 1M Watt, 25 mm2
    b) 1K Watt, 16 mm2
    c) 1M Watt, 16 mm2
  2. jcsd
  3. Jul 4, 2011 #2


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    Science Advisor

    Welcome to PhysicsForums!

    Why don't you show us what you're thinking, and then we can help you with your solutions?
  4. Jul 4, 2011 #3

    A agree, the problems are too easy (the third is the hardest), you have only to interpret the question. How can we explain the third problem to you if you don't even know how to work with %. Show us your work !
  5. Jul 4, 2011 #4
    dear all I need to know the rules and equations or the idea because I forget this kind of problems and I want to remember them.
    Please help me as much as you can with everything to remember how to solve it.
  6. Jul 4, 2011 #5


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    Staff Emeritus
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    Gold Member

    What is 2% of 100 ?
  7. Jul 4, 2011 #6


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    Science Advisor

    These are mostly definition and simple rate-type equations. What sort of review is it that you're doing?

    1) How does an error as a percentage of the full scale compare to an error as a percentage of the reading compare to an error in the least-significant digit?

    2) This is just dealing with percentages (except for the current, where you need to use an offset as the current doesn't go to zero).

    3) Work is force over a distance. To lift a cubic meter of water by 1 meter, you'd have to work against gravity. You can also use the potential energy you'd have to imbue on the water to get it to the height via the formula [itex]E=m*g*h[/itex] Conveniently, the height is given as:
    [itex]\frac{1000}{9.8}[/itex] m

    Since power is energy per second, this allows you to determine the current and apply a safety factor.
  8. Jul 4, 2011 #7


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    Staff: Mentor

    You need to show some effort and work on these problems, or this thread will be deleted.

    We do not do your homework for you here on the PF.
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