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Rudder indicators


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#11 Black Panther

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Posted 12 June 2018 - 07:57 PM

My rudder angle indicator lies. So do my wind instruments. I find it helps not to look at them.
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#12 Chrisc

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Posted 12 June 2018 - 08:25 PM

Thanks BP, I agree that it's a wiring issue. The problem is that the power off position of the needle is hard to starboard. Powered up, the mis-reading gauge shows 15 degrees to port with rudder midships which would then indicate excessive voltage?
I wonder if the top deck rudder system is over-earthed, possible? A wiring diagram I found online shows the system earthed at the rudder sender unit with an optional earth at the gauge. My set up has both positions earthed.
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#13 wheels

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Posted 13 June 2018 - 05:59 AM

No it is likely that it is "under earthed" err for use of a bad description. This maybe difficult to explain, but in effect, the Earth pulls back the voltage.
You couldn't have a gauge system where the Main Ships voltage is across the Gauge and Resistor as such. Because then when the wiper reached Earth, there would be a dead short to ground and the wiring would melt. So there is a small signal voltage applied to the system parts, which is called "signal". Sometimes gauges tend to work in reverse to what you would think, in that full scale deflection is actually the lowest voltage and that the high voltage actually pulls the gauge back. So a poor earth ends up reading high.
So, if you are experiencing fluctuations with the Key and engine running etc, then this actually makes a little sense now that you say the system is earth at two points. It may not be the Gauge Earth that is the issue, but the main Earth feed itself. Check that the main Earth to the instruments is properly connected at both ends. There is a "voltage drop" on the feed for some reason. Turning the Key is placing a load on the Earth, but the earth is not able to pull right down to zero.
I hope that made sense.


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#14 Chrisc

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Posted 13 June 2018 - 06:29 AM

No, I'm afraid it doesn't but that's my fault, not yours. Electricity is confusing! However, I will follow your advice and check out the earth connections.
Joke says why don't I save myself all the heartache and just scratch a line on the upper indicator bezel where the instrument shows the midships helm position.
She's right and it makes sense, it's just that misbehaving equipment drives me crazy.
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#15 Jon

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Posted 13 June 2018 - 07:06 AM

I was about to suggest you put a little arrow sticker on center for the one that’s out but I was beaten by Joke
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#16 wheels

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Posted 13 June 2018 - 08:27 AM

And as the connection worsens, the needle is going to move across further and eventually you are not going to be able to read it with all the updated scratch marks. ;-)
Sorry to have made that explanation confusing. To summerise, sounds like a bad earth. check all Earth connections.

You may even find that other gauges could shift their position if they were all attached to the same Earth.


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#17 mattm

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Posted 13 June 2018 - 12:09 PM

I’d eye ball the wiring sure, but my first actual task after that would be swapping the gauges.

I think the bit you missed Chris, was that either gauge could be misreading. If you rotate the base of the RPS 15 deg to starboard, the ‘wrong’ gauge will be right, and the ‘right’ gauge will read 15deg to starboard and now be wrong. Assuming it’s the gauge for a minute, what you want is two gauges that read the same at any given resistance, then you set the RPS to read center when is centered.
The simplest check you can do, with limited understanding of power, is swap the gauges over and report the findings. Or, perhaps fitting the spare gauge in the position of the ‘correct’ gauge would tell a story also, wouldn’t be my preference though unless the gauges are a PITA to remove, which often they can be.
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#18 Chrisc

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Posted 15 June 2018 - 04:38 AM

I am pleased to advise that the rudder indicator issue is now resolved. As with a lot of these type problems the issue was one of human error, essentially mine.
I don't know how I missed it but the two installed gauges were slightly different which made me think different gauges, perhaps different signal voltages. Changing the odd-man-out gauge and installing the spare to match the other one installed solved the problem. Both reading the same now, Thank goodness.
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#19 Winter

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Posted 15 June 2018 - 09:03 AM

Glad to hear it is solved.
some of the vdo indicators do actually have an adjustment pot, however it is set at the factory and not accessible.
if you carefully drill a hole in the side of the housing you can shine a light in and look, you can then workout where on the housing the pot is, and drill another hole right above that.

I have a VDO voltmeter I adjusted in this way
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#20 Chrisc

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Posted 15 June 2018 - 05:44 PM

Thanks Winter. That's a handy bit of info.
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