# Question about frequency counters and circuits

1. Apr 2, 2005

### mathlete

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?

Last edited: Apr 2, 2005
2. Apr 4, 2005

### Delta

How is it being used???

Is it a frequency counter IC?, A RPM counter?, a electromechanical lap counter?

3. Apr 4, 2005

### faust9

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

4. Apr 4, 2005

### waht

re

Some of the Agilent (Hewlett Packard) counters can switch between a 50 Ohm and a high impedance input. But those cost big bucks.

5. Apr 5, 2005

### pack_rat2

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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