Download Professional Literacy Development, Electrical Measurements

Professional Literacy Development, Electrical Measurements - G3A and G3B
Read the text and complete the exercises.
Electrical Measurements
Measurements in Engineering are necessary for the development, production, and use of accurate and reliable
real world solutions. In Electrical Engineering, voltage, current and resistance are three important quantities
that need to be measured accurately. Wrong measurements are often the cause of technical faults in electrical
and electronic systems.
Voltmeter
A voltmeter measures the change in voltage between two points in an electric circuit and therefore must be
connected in parallel with the portion of the circuit on which the measurement is made.
Ammeter
An ammeter is an instrument for measuring the electric current in amperes in a branch of an electric circuit. It
must be placed in series with the measured branch, and must have very low resistance to avoid significant
alteration of the current it is to measure.
Ohmmeter (Voltmeter/Ammeter Measurements)
The value of electrical resistance associated with a circuit element or appliance can be determined by
measuring the voltage across it with a voltmeter and the current through it with an ammeter and then dividing
the measured voltage by the current. This is an application of Ohm's law.
Analogue displays
Meters with analogue displays have a pointer which moves over a
graduated scale. They can be difficult to read because of the need to
work out the value of the smallest scale division. They are useful for
monitoring continuously changing values (such as the voltage across a
capacitor discharging) and they can be good for quick rough readings
because the movement of the pointer can be seen without looking
away from the circuit under test.
To take an accurate reading from an analogue scale you must have your
eye in line with the pointer. Avoid looking at an angle from the left or
right because you will see a reading which is a little too high or too low.
Many analogue meters have a small strip of mirror along the scale to
help you. When your eye is in the correct position, the reflection of the
pointer is hidden behind the pointer itself. If you can see the reflection,
it means you are looking at an angle and will record a wrong reading.
Digital displays
Values can be read directly from digital displays so they are easy to read
accurately. It is normal for the least significant digit (on the right) to continually
change between two or three values. This is a feature of the way digital meters
work, not an error. If you do not need great precision, the least significant digit
can be ignored or rounded up.
Adapted from: http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
1. Answer the questions according to the text.
1. Why are measurements necessary in Engineering?
2. How are voltmeters connected?
3. What are ammeters used for?
4. Why must ammeters have low resistance?
5. How can Ohm’s law be applied to measure electrical resistance?
6. What are meters with analogue displays useful for?
7. Give one disadvantage of analogue displays.
8. Why do some analogue displays have a small strip of mirror along their scale?
9. Give one advantage of using meters with digital displays.
2. Vocabulary
Translate these key words in Slovene and write down their definitions in English.
Key word in English
measurement
Engineering
meter
voltmeter
ammeter
ohmmeter
parallel connection
series connection
analogue
digital
Key word in Slovene
English Definition