# indicators

Discussion in 'Homework Help' started by conehed, Jan 14, 2008.

1. ### conehed Thread Starter Member

Jan 9, 2008
11
0
Good Evening all.
I am currently studying HND BS(E) and have got my first research project! Hoorah!! NOT! lol- anyway- anyhelp/links would be gratefully received.

OK where to start.... We are currently on the DC phase, but some of the questions relate to both DC and AC. This assignement is called, funnily enough, "INSTRUMENTATION RESEARCH ASSIGNMENT".

QUESTION 1:

" Many power measurement indicators can be categorised into the following types:

a. Electrodynamic indicators.

b. Thermocouple indicators.

c. Induction indicators.

Describe the function/operation of each type."

That is the exact question- cut 'n' pasted

Thankyou

Apr 20, 2004
15,815
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3. ### hgmjr Moderator

Jan 28, 2005
9,030
214
conehed,

The three terms you have listed would make more sense, to me anyway, if the word "indicators" were replaced with the word "sensors".

Do you think that would be an absurd substitution to make?

hgmjr

4. ### conehed Thread Starter Member

Jan 9, 2008
11
0
hi all- thanks for your time.

The three terms you have listed would make more sense, to me anyway, if the word "indicators" were replaced with the word "sensors".

mmmmmm- unknown- the questions to research are all very broad and the questions are exactly cut and pasted- so to rename indicators would surely mean the answer would be incorrect, however i will pose the question to the instructor tomorrow.

As for finding aswers so far- we are thinking along the following lines!!! Can anyone see a problem from the angle we are looking at it from?....

a. Electrodynamic indicators.

Electrodynamic Indicators. Electrodynamic indicators comprise of 2 current coils connected in series and a movable potential coil connected in parallel. The potential coil carries a needle used to indicate the power set against a calibrated scale. As current is passed through the current coils it generates an electro-magnetic field (emf) that is proportional to the line current. In a Direct Current (DC) circuit this indicates power as the deflection of the needle is proportional to the current and the voltage. In an Alternating Current (AC) circuit the emf is proportional to the instantaneous product of the voltage and current which indicates the true power.

b. Thermocouple indicators.

Thermocouple Indicators. As one end of a piece of metal is subjected to a change in temperature, electrons become free from the atoms and migrate towards the cooler end of the metal, generating a voltage. The voltage generated is dependant on the atomic structure of the metal, therefore different metals generate different voltages. A thermocouple is based on this principle. In a closed circuit with two different metal elements, current will flow due to the difference in voltages. In a thermocouple, the circuit is broken with a sensitive voltmeter attached to measure the thermo-electric voltage of the loop. The voltage is due to a change in temperature which, inturn, is due to the Radio Frequency (RF) power across the thermocouple element.

c. Induction indicators.

Induction Indicators. An induction meter functions by recording the number of revolutions of an aluminium disc. The disc is acted upon by 2 coils, each producing a magnetic flux. The flux generated by one coil is proportional to the voltage, and the remaining coil produces a magnetic flux proportional to the current. A lag coil is used to delay the field of the voltage coil by 90º. The resulting eddy currents exert a force on the aluminium disc forcing it to rotate in proportion to the voltage and the current. A permanent magnet exerts an opposing force, proportional to the rotational speed of the disc, causing it to stop when power stops being drawn and preventing it from accelerating. The coils in conjunction with the magnetic brake make the disc rotate in proportion to the power being used.

5. ### conehed Thread Starter Member

Jan 9, 2008
11
0
Thanks to allaboutcircuits for the information i gained on this DC Phase assignment- it has been passed at 84%. I will attach a copy for any future reference should anyone wish to do so. I understand that one or two may be incorrect, but as an assignment it passed. Now onto the next phase.........AC!

6. ### conehed Thread Starter Member

Jan 9, 2008
11
0
sorry guyz- tried to split up the word doc into 2 parts to each was below 2MB but neither will upload- sorry