PMMC measuring Instrument reading

Click For Summary

Discussion Overview

The discussion revolves around the readings of a PMMC (Permanent Magnet Moving Coil) measuring instrument and a MI (Moving Iron) instrument in the context of a specific homework problem involving diodes and voltage measurements. Participants explore the implications of the circuit configuration on the expected readings of these instruments.

Discussion Character

  • Homework-related, Technical explanation, Debate/contested

Main Points Raised

  • One participant believes that the PMMC should read 0 V, while the book states it should read 1 V, questioning where their reasoning went wrong.
  • Another participant suggests that the question is flawed, arguing that if the diodes are ideal, they would short the supply when forward biased, affecting the voltmeter's reading.
  • A participant reiterates the idea that the question may have intended to depict a diode bridge, asserting that in such a case, the PMMC would read 1 V instead of 0 V.
  • There is a clarification about the diode bridge being a full wave rectifier bridge, with a participant stating that for a square wave input, the PMMC should read an average of 1 V and the MI should read an RMS of 1.414 V.

Areas of Agreement / Disagreement

Participants express differing views on the validity of the question and the expected readings of the instruments, indicating that multiple competing interpretations exist regarding the circuit configuration and its implications.

Contextual Notes

There are unresolved assumptions about the ideality of the diodes and the specific configuration of the circuit, which may influence the readings of the measuring instruments.

jaus tail
Messages
613
Reaction score
48

Homework Statement


upload_2018-1-22_19-47-0.png


Homework Equations


For question 14
PMMC measures average value
MI measures RMS value

The Attempt at a Solution


I think PMMC should give 0 V But book answer is B i.e 1 V (where am I wrong?)
and MI should give 1.414 V. For this book answer matches my answer.
 

Attachments

  • upload_2018-1-22_19-47-0.png
    upload_2018-1-22_19-47-0.png
    7.8 KB · Views: 938
Physics news on Phys.org
I think the question is flawed.
If the diodes are considered to be ideal:
Two diodes on the same side (either left or right) of the voltmeter get forward biased simultaneously and short the supply.
At the same time, the reverse biased diode pair effectively disconnects the voltmeter terminal connected to it from the voltage source.

I guess this was meant to be a diode bridge and got printed incorrectly.
 
  • Like
Likes   Reactions: jaus tail
cnh1995 said:
I guess this was meant to be a diode bridge and got printed incorrectly
And if it were a diode bridge, the PMMC meter would indeed read 1V, not 0V.
 
By diode bridge you mean full wave rectifier bridge?
upload_2018-1-23_13-43-20.png

I think if input is square wave then Voltmeter should read average which is 1 V
MI should read rms which will be 1.414 V
 

Attachments

  • upload_2018-1-23_13-43-20.png
    upload_2018-1-23_13-43-20.png
    2.6 KB · Views: 391

Similar threads

Is it maximum voltage or RMS voltage
  • · Replies 8 ·
Replies
8
Views
4K
How PMMC and MI Instruments Read Average Values for DC Waveforms
  • · Replies 10 ·
Replies
10
Views
3K
Measurement (didn't understand solution)
  • · Replies 1 ·
Replies
1
Views
1K
Calculate Real and Reactive Power and write equation for S = P + jQ
  • · Replies 7 ·
Replies
7
Views
6K
Engineering Source impedance using given voltage swing and power
  • · Replies 2 ·
Replies
2
Views
2K
Calculate Power Using RMS Voltage & Current
  • · Replies 2 ·
Replies
2
Views
2K
Oscilloscope Error: Measuring Sinusoidal Wave
  • · Replies 1 ·
Replies
1
Views
2K
What is the definition of changed point in geomatics?
  • · Replies 5 ·
Replies
5
Views
1K
RMS or Average Current Homework - Tips & Tricks
  • · Replies 6 ·
Replies
6
Views
3K
Finding Steady State Amplitude of Voltage Across Load Resistor
  • · Replies 3 ·
Replies
3
Views
3K