# Checking tangency state of crunode.

• posted

My vintage probe-style multimeter started playing up and I decided it was time to replace it.

I got a new one from Jaycar - QM-1498.

It has one slide switch and four push-buttons on it. One of the buttons is marked "LI". As far as I can fathom, LI stands for "Low Impedance", and it appears that pressing this button while in AC or DC volt mode connects an extra resistor across the probes to reduce the normal 10M input resistance to 400K. The leaflet says that this "may check the tangency state of the crunode".

Wikipedia tells me that a crunode is a point on a self-intersecting curve where there are two distinct tangents. However this does not help me to understand how to measure the tangency state.

Actually I don't even know when or why I would want to do that, so I'm not sure why a relatively inexpensive multimeter would have a special button to help me do it.

Can anybody enlighten me?

Andy Wood snipped-for-privacy@trap.ozemail.com.au

• posted

Hmmm, how does this interpretation sound?: If the resistor loads the circuit the waveform height would be lower under load IOW it will be "Checked" using another meaning of the word checked. If the wave height is lower then the tangents would change and the so would the crunonde.

This changing crunode must obviously be how guitarists get their guitar amplifier to sound "Crunchy".

• posted

. . .

Well, it looks like nobody has a better explanation, so you may be right.

I found that some Fluke meters have a what they call the 'LoZ' function which reduces the meter impedance, apparently down to about

3K, rather than the stated 400K of the Jaycar meter. As far as I can see, Fluke don't go off an a tangent talking about crunodes though. Instead they suggest that sparkies could use use this function for ghost busting (not getting mislead by voltage readings on non-energised wires due to capacitive coupling from adjacent energised wires).

Andy Wood snipped-for-privacy@trap.ozemail.com.au

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