Why does tapping on a guage make it read correctly?

[m32825]

I spent a few hours today doing my part to keep Central Florida warm with my 803 and oven. While I was load testing I kept seeing the Hz gauge slide down a few half-Hz ticks. If I tapped on the gauge it would straighten up and fly right for a while (probably waiting for me to stop looking at it) then go low again. What does tapping do that makes a guage read correctly?

-- Carl

 

[Suprman]

Sounds like the gage is going bad and was sticking. You tapping on it got it to move. May it may not read correct now. I would replace the gage.

 

[Light in the Dark]

Have you checked the rear connections?

 

[Floridianson]

Wakes up the Gerbils.

 

[NormB]

Sticky gauge needles have a long, storied history.

Back when I was first taking flying lessons (gliders, single engine light planes, rare stick time in helicopters), I asked what the buzzing sound from the instrument panel was. Turns out the altimeters are prone to sticking and this crucial value can ruin your day real quick with a CFIT event (Controlled Flight Into Terrain) if you're not paying attention or flying under IFR.

So manufacturers put mechanical "tappers" inside to "unstick" the needles so the pilot can do other things.

 

[Floridianson]

Sticky gauge needles have a long, storied history.

Back when I was first taking flying lessons (gliders, single engine light planes, rare stick time in helicopters), I asked what the buzzing sound from the instrument panel was. Turns out the altimeters are prone to sticking and this crucial value can ruin your day real quick with a CFIT event (Controlled Flight Into Terrain) if you're not paying attention or flying under IFR.

So manufacturers put mechanical "tappers" inside to "unstick" the needles so the pilot can do other things.

Last time I was in a glider the buzz noise was a good thing!

 

[m32825]

Thanks for the replies, guys. While I was load banking I had a digital Hz meter hooked up and it was steady. The analog gauge would slowly work lower a couple Hz over time. At first I wondered: what makes it move lower? Then I remembered to try tapping on it and that fixed it for a bit. After doing that a few times I wondered: why does that fix it?

-- Carl

 

[tennmogger]

Tapping works because dynamic friction is less than static friction.