Question about frequency counters and circuits

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Discussion Overview

The discussion revolves around the properties of frequency counters and their impact on circuit measurements. Participants explore the necessary characteristics of frequency counters to ensure accurate readings without affecting the circuit being measured.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about the necessary properties of frequency counters to avoid affecting circuit measurements, drawing a parallel to the low resistance required for ammeters.
  • Another participant asks for clarification on the specific application of the frequency counter, suggesting different types such as ICs, RPM counters, or electromechanical lap counters.
  • It is proposed that frequency counters should ideally have high input impedance to prevent loading the circuit, similar to ohmeters, with practical values typically ranging from 1M to 10M ohms.
  • A later reply mentions that some Agilent counters can switch between a 50 Ohm and a high impedance input, although these models are noted to be expensive.
  • One participant points out that a common source of error in frequency counters is triggering on noise, which does not affect the circuit itself, and suggests that careful adjustment of the trigger or sensitivity can enhance accuracy.

Areas of Agreement / Disagreement

Participants express varying views on the necessary properties of frequency counters, particularly regarding impedance and error sources. There is no consensus on a single approach or solution.

Contextual Notes

Some assumptions about the specific application of frequency counters remain unclear, and the discussion does not resolve the potential impact of different counter types on measurement accuracy.

mathlete
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I'm trying to figure out something about frequency counters. When you hook up one up to a circuit, what property of the counter is necessary so it doesn't affect the measurement of the circuit - for example, an ammeter has to have a very low resistance, etc.

edit: I really don't see what this has to do with electrical engineering, I guess all question's pertaining to Ohm's law are not physics now?
 
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How is it being used?

Is it a frequency counter IC?, A RPM counter?, a electromechanical lap counter?
 
Frequency counters should have high(ideally infinite) input impedence to prevent loading the circuit--Just like an ohmeter.

In practice you'll find thay(like ohmeters) have 1M to 10M of impedence(give or take a little).

Here's a simple one if you want to look over the schematics: http://www.piclist.com/techref/piclist/weedfreq.htm
 
re

Some of the Agilent (Hewlett Packard) counters can switch between a 50 Ohm and a high impedance input. But those cost big bucks.
 
The main source of error with counters is that they can trigger on noise. But this isn't something that affects the circuit. Careful adjustment of the trigger or sensitivity control can improve accuracy.
 

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