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David Simpson · 7th Oct 2019, 10:45 am

Graham, you're fortunate that the meter's FSD has fallen slightly short of 30uA, rather than gone beyond, when tested outside the meter. Gives you the opportunity to alter the shunt resistance a tad.
If you're now happy with the meter's mechanical zero, and the issue is just with getting true "Set ac" - have you checked the 55V winding to see that its voltage is spot on(with the pri. tappings adjusted to your mains voltage) ? Sometimes its a bit of a balancing act between RV3 & the wee slider sw to get centre of the black set ac zone(27.5uA), & maintain 55V.
After all - its the 55V derived grid -ve "pulse" that is critical for "Test" procedures.

Regards, David

7th Oct 2019, 10:45 am	#6
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,859	Re: AVO CT160. Meter over reading. Graham, you're fortunate that the meter's FSD has fallen slightly short of 30uA, rather than gone beyond, when tested outside the meter. Gives you the opportunity to alter the shunt resistance a tad. If you're now happy with the meter's mechanical zero, and the issue is just with getting true "Set ac" - have you checked the 55V winding to see that its voltage is spot on(with the pri. tappings adjusted to your mains voltage) ? Sometimes its a bit of a balancing act between RV3 & the wee slider sw to get centre of the black set ac zone(27.5uA), & maintain 55V. After all - its the 55V derived grid -ve "pulse" that is critical for "Test" procedures. Regards, David