Multimeter (VOM) Design in Electronics Engineering

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Discussion Overview

The discussion revolves around understanding the operation and design of a volt-ohm meter (VOM) in the context of electronics engineering. Participants are exploring the principles behind voltage measurement, the configuration of a VOM, and how to approach related homework problems.

Discussion Character

  • Homework-related
  • Technical explanation
  • Exploratory

Main Points Raised

  • Some participants express confusion about how a VOM operates, particularly regarding the maximum scale value and the concept of a voltage divider when a resistor is attached.
  • One participant suggests a formula for calculating output voltage based on internal resistance and load resistance, indicating a basic understanding of the circuit behavior.
  • Another participant describes the VOM configuration as having a 50μA output test current monitored by an infinite input impedance voltmeter, linking this to the external resistance producing a test voltage of 1V.
  • There are requests for visual aids, such as schematics, to clarify the operation of a VOM, indicating a need for simpler explanations or representations.
  • Terminology issues are noted by one participant, who expresses uncertainty about understanding the questions posed in the homework.

Areas of Agreement / Disagreement

Participants generally express confusion and seek clarification on the operation of a VOM, indicating that there is no consensus on the understanding of the topic. Multiple viewpoints and interpretations of the VOM's functionality are present.

Contextual Notes

Some participants mention specific values and configurations (e.g., 50μA, 20kΩ, 1V) without fully resolving how these relate to the overall operation of the VOM, suggesting that assumptions about the circuit's behavior may not be fully articulated.

nebbione
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Homework Statement


The statement is this one... (from the horowitz "The Art of Elctronics")
http://www.electroyou.it/forum/download/file.php?id=13691


Homework Equations


How should I proceed, i really didn't understand how this VOM works, i mean, i understood, that there a max scale value of a VOM which in this case is 1V, so when i attach a resistor, a voltage divider is created, and I'm going to read the value of voltage on the internal resistance of my voltmeter, is this right ? And how is the second point of the exercise solved?
Can you explain me how this works? and what does it mean a VOM 50μA 20kΩ/1V ??


The Attempt at a Solution


I think it's right for the first point to proceed like this :

Vout=Vin*(Rint/Rint+Rload)

but for the second point i have no idea...
 
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nebbione said:

Homework Statement


The statement is this one... (from the horowitz "The Art of Elctronics")
http://www.electroyou.it/forum/download/file.php?id=13691


Homework Equations


How should I proceed, i really didn't understand how this VOM works, i mean, i understood, that there a max scale value of a VOM which in this case is 1V, so when i attach a resistor, a voltage divider is created, and I'm going to read the value of voltage on the internal resistance of my voltmeter, is this right ? And how is the second point of the exercise solved?
Can you explain me how this works? and what does it mean a VOM 50μA 20kΩ/1V ??


The Attempt at a Solution


I think it's right for the first point to proceed like this :

Vout=Vin*(Rint/Rint+Rload)

but for the second point i have no idea...

Your link is not working for me, and the website has some pretty dubious advertisements. Can you upload an image of the problem? Or sketch it yourself and upload it?

You are not authorized to view, download, or insert links to / from this site.
 
http://postimage.org/image/wkzxm7ro1/ sorry, here you are !
 
nebbione said:
http://postimage.org/image/wkzxm7ro1/ sorry, here you are !

Your second link is worse than the first. Can you just upload the image as an attachment please? The advertisements in those pages are quite risque.
 
here you are !
 

Attachments

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Thank you. It looks like they are defining the VOM configuration as a 50uA output test current that is monitored by an infinite input impedance voltmeter. So that's why an external 20kOhm resistance will produce a test voltage of 1V.

So I would approach these questions as having a 50uA current source (from some higher voltage) driving the loads that they mention. So for the first question, draw the circuit as a 50uA current source driving down into a 10k resistor and a 1V power supply. What voltage would you then see at the junction of the current source output terminal and the input of the 10k resistor?

And for the second question, the 50uA current source drives the mid-point of the voltage divider. What voltage would be measured between the low-side output of the current source and ground?

(TBH, I'm not sure I'm understanding this question because of the terminology issue. I'll ask for help from other HH'ers to check this.)
 
anyway i still didn't understand how a VOM works, can you put me a very simple and basic schematic telling me how does it works ?
 

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