ebay panel voltmeter accuracy and a question..

[GHA]

8 quid from eBay , could it be any good?
http://www.ebay.co.uk/itm/Digital-V..._Measurement_Equipment_ET&hash=item4aab51b377

And surprisingly accurate.




And...... I've been messing about with bits of broken boats for a while now and accumulated a fair chunk of handy test kit. As much a hobby as nothing (buying stuff off Ebay that is )
And it would be nice to recoup some of the cost in some sort of minor way. So was thinking of maybe making up some flyers to put up in the shower block etc. Very low key, for beer or barter sort of thing. Though karma works IMHO , lend a hand and unexpected good things happen back.


Mostly lx stuff, various meters, dc clamp meter to track down missing amps or just how many amps, tiny oscilloscope for tracking nmea data or ac where it shouldn't be, plus a USB scope coming soon. And a newly found obsession, arduinos for logging temp, current or voltage to a sd card over time & battery capacity test.
So what you think? Worth doing?
Just created a rather grand Google id of boatdatasystems
Or anyone round the Thames with problem where lots of measuring might help? Petrol money from Kent I'd be up for it, non commercial.

Cheers and hope this isn't breaking any forum rules.

 

[BruceDanforth]

It will be precise but not necessarily accurate. Consider a null method with a potentiometer and galvanometer if you want real accuracy. Don a white lab coat and wander up and down the pontoons with it....

 

[mjcoon]

It will be precise but not necessarily accurate. Consider a null method with a potentiometer and galvanometer if you want real accuracy. Don a white lab coat and wander up and down the pontoons with it....

You'd still need an absolute reference voltage! Not a "standard cell" from my old physics course, surely?

Mike.

 

[GHA]

It will be precise but not necessarily accurate.

Don't quite understand that?? It's within 30mV of the Fluke, which seems pretty accurate...

 

[GHA]

You'd still need an absolute reference voltage!

Some of these on the way....

http://pages.ebay.com/link/?nav=item.view&id=271177863521

 

[BruceDanforth]

Yes but the 2 meters have become part of the circuit you are measuring and changed it....a tiny current is flowing through them

The fluke will have a huge internal resistance and won't disrupt the circuit much.

The 8 quid thing? Who knows what the internal resistance will be. It will be OK but nothing like the fluke so don't confuse 3 figure precision with 3 figure accuracy.

Don't quite understand that?? It's within 30mV of the Fluke, which seems pretty accurate...

 

[GHA]

Yes but the 2 meters have become part of the circuit you are measuring and changed it....a tiny current is flowing through them

The fluke will have a huge internal resistance and won't disrupt the circuit much.

The 8 quid thing? Who knows what the internal resistance will be. It will be OK but nothing like the fluke so don't confuse 3 figure precision with 3 figure accuracy.

It makes no difference if the meters are connected one at a time or both together, the readings don't change. How can 2 meters read the same and one be inaccurate ?

 

[elton]

It makes no difference if the meters are connected one at a time or both together, the readings don't change. How can 2 meters read the same and one be inaccurate ?

If you connect both meters to a voltage source that has a low (internal) resistance, they'll probably both read the same. If you connect the same meters to a voltage source that has a high resistance, you might find that one of the meters reads under because it has a relatively low resistance.

 

[BruceDanforth]

deleted 'cos Eltons explanation was clearer than mine which was waffly and a bit wrong...

 

[nigelmercier]

... oscilloscope for tracking nmea data or ac where it shouldn't be, plus a USB scope coming soon.

Doesn't everyone already have an oscilloscope on board?

I like your idea of flyers to offer help. It can be so frustrating to know what tool you need, and that you don't have one with you. Perhaps this is why I do have an oscilloscope on board, very handy http://amzn.to/1gC1h4R

 

[GHA]

If you connect both meters to a voltage source that has a low (internal) resistance, they'll probably both read the same. If you connect the same meters to a voltage source that has a high resistance, you might find that one of the meters reads under because it has a relatively low resistance.

Where would I find one of those onboard, I'll give it a go.

Both meters within 20mA on the main batteries. Which is the idea. One cost 8 quid, the other 70.

Sort of feels like I've wandered into the negativity societies AGM on here......

 

[nigelmercier]

Sort of feels like I've wandered into the negativity societies AGM on here......

Don't feed them after midnight

 

[GHA]

Doesn't everyone already have an oscilloscope on board?

I like your idea of flyers to offer help. It can be so frustrating to know what tool you need, and that you don't have one with you. Perhaps this is why I do have an oscilloscope on board, very handy http://amzn.to/1gC1h4R

With a scope and a dc clamp meter you can track down an awful lot, I have one of these already and a USB scope coming....
http://www.ebay.co.uk/itm/like/4005...ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=95&ff19=0


This is what a cheap inverter looks like...

 

[JumbleDuck]

If you connect both meters to a voltage source that has a low (internal) resistance, they'll probably both read the same. If you connect the same meters to a voltage source that has a high resistance, you might find that one of the meters reads under because it has a relatively low resistance.

And if you connect them at the same time?

 

[Telstar26]

Have a look at the SparkBright voltage monitors - http://www.sparkbright.co.uk/products.html. A nice simple way of keeping an eye on the battery voltage.

 

[VicS]

Doesn't everyone already have an oscilloscope on board?

Gosh I knew there was some vital bit of equipment I was missing.

I wonder how I got by all these years without one.



Must go out and buy one without delay ...

Something like this

.... or can I convert an old tele?

 

[sarabande]

this has sparked (ha!) a memory of Pico oscilloscopes.


A piece of hardware with various probes which you attach to a laptop.

http://www.picotech.com/picoscope2000.html

and lo and behold, there are even oscilloscopes for th eiphone.

https://itunes.apple.com/gb/app/oscilloscope/id388636804?mt=8


Does anyone have experience of either system please ?



TIA

 

[aquaplane]

I fitted one of those £8 jobs from EBay and it seems to work OK. Access to the batteries with the multi meter was/is poor so I fitted one instead. I fitted a switch so I could test the engine battery or the domestic one.

I was told that I really needed a £100+ battery monitor but I ignored that advice and bought a beer, and quite a lot of other stuff too.

 

[mjcoon]

Gosh I knew there was some vital bit of equipment I was missing.

I wonder how I got by all these years without one.

Must go out and buy one without delay ...

Something like this
.... or can I convert an old tele?

That dinky little 'scope looks as though it has a small version of the six-inch VCR97 radar tube my Dad used to construct the TV on which we watched the coronation. (Trying to ignore that the Queen, and everyone else, were green!)

I still have the last of his VCR97s because as a school-boy I built it into a home-made oscilloscope.

I also have an elderly Philips digital storage 'scope which would, to edge back towards boats, make good ballast...

Converting a TV, especially if old, would not be trivial! (It's the magnetic beam deflection, don'cha know.)

Mike.

 

[elton]

Where would I find one of those onboard, I'll give it a go.

Both meters within 20mA on the main batteries. Which is the idea. One cost 8 quid, the other 70.

Sort of feels like I've wandered into the negativity societies AGM on here......

If you don't understand the difference between precision and accuracy, it's probably best you leave the measuring to someone who does.