mismeasurement multimeter MEGGER

Thread Starter

spacecadet88

Joined Jun 15, 2019
3
Hi guys, I have a megger multimeter (AVO310) my problem is that it gives measurements without there being anything connected, the battery check it and try a new one and the problem continues, it's a gift, when I opened it to review it I realized that a resistance was bridged, I would like to fix it, but I do not know the value of that resistance, is there someone who can help me? occupy the search engine without good results. Thank you very much, I attach images. Greetings.


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Thread Starter

spacecadet88

Joined Jun 15, 2019
3
I repeated the welding on the right, but it's still the same, I do not think it's a resistor chunt, or maybe if, what I'm sure is that it's not original, it was soldered on one side and because of the quality of the welding and the cable of copper is not original, I attach more images and thanks for the answers, I am very grateful.

6.jpg 7.jpg
 

sagor

Joined Mar 10, 2019
207
R69 IS a current shunt, not a "resistance bridge". Passing larger amounts of current produces a smaller millivolt reading, which the meter uses to display the current.
These wire shunts are usually very low resistance (0.1 ohm or less), and are a specific length to give an exact shunt resistance. At 10A, a 0.1 ohm shunt will give 1.0V full scale reading. A 0.01 ohm shunt will give a 100mV value for the meter to read and display (properly scaled for the 10A range.
It is even possible it is a 1 ohm shunt, and the meter reads the 0-10V for 0-10A and displays that as the current reading.
The fact that it seems desoldered means it was either not assembled right, or someone passed a huge current surge through it, enough to heat up the shunt. Usually a fuse prevents this.... You seem to have a 10A fuse in that meter, that should have blown if too much current was passed thru the current shunt.

Thus, that current shunt is probably not the cause of your random readings problem, you have to look elsewhere... (but do fix that shunt so it works properly)
 

dendad

Joined Feb 20, 2016
3,528
Some electronic soldering paste flux on the shunt joint may help it solder better. But it could just be the shunt was soldered in with an iron that did not have the heating capacity to fully heat the joint so the solder could flow. It is a pretty horrible looking joint!
 

KL7AJ

Joined Nov 4, 2008
2,225
Hi guys, I have a megger multimeter (AVO310) my problem is that it gives measurements without there being anything connected, the battery check it and try a new one and the problem continues, it's a gift, when I opened it to review it I realized that a resistance was bridged, I would like to fix it, but I do not know the value of that resistance, is there someone who can help me? occupy the search engine without good results. Thank you very much, I attach images. Greetings.
https://imgur.com/4jXIXzH
https://imgur.com/vaWAx23
https://imgur.com/INFBhnR
Also be sure everything is super super clean. Wipe the entire outside of the cabinet down with alcohol, and then a coating of silicon lube spray. If it's been sitting around for a while, minuscule amounts of dust and crud can create a conductive path. Which is exactly what a megger is sposta measure.
 
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