Testing Accuracy of a 0.25 Water Manometer Using a 10:1 Inclined Mount

[Asymptotic]

"outlined, 3% of full scale is +/- 0.008" w.c. (0.008" in 0.25") so obtaining accurate measurements down to 0.02" w.c. is problematic in either case." The gauge I referenced is FS accuracy 2% which is 0.005. I am ok with +/-0.005.

Could be I'm looking at this incorrectly, but not per Dwyer bulletin A-27, and specs at the web page for series 2000 gauges. The model xxxx-0 is 3%.

Accuracy:
±2% (-HA model ±1) of FS (±3% (-HA ±1.5%) on -0, -100PA, -125PA, -10MM and ±4% (-HA ±2%) on -00, -60PA, -6MM ranges), throughout range at 70°F (21.1°C).

 

[paulmars]

maybe u right. I am unhappy with dwyer email support on other issues. I asked what the accuracy was, since their page lists 2,3, and 4%. response was for that specific unit 2%. Still, I don't like used and new costs too much. Interesting is that dwyer also lists the same 3% for mark ii mdl 25 and for mark ii mdl 40-1 of 3% FS. So, 40-1 would be more accurate. I wonder why both have same stated FS accuracy.

3% of 1.0 is 0.03 and that is not accurate enough and no one is recommending this unit and I wonder why.

 

[sophiecentaur]

However, the accuracy makes it really useless.

I cannot believe that a simple oil heater can require the sort of measurement accuracy that you suggest. If the concern is the rate of flow of exhaust gases then there will be many other factors involved than pressure. Tolerances can't be particularly tight. The flue layout spec for most boilers has some recommendations about length and bends which are pretty non demanding.
I suggest you visit a plumbing and heating forum and ask what they all do. Be prepared for a less friendly response when you actually suggest DIY for anything to do with heating. They will probably tell you to get it done 'professionally' and then go on to explain things in impossible non-Science terms. The words "idiot" and worse are to be expected if you suggest taking the bread out of their mouths but you may get the name of a suitable instrument from someone before the sky falls in.

You wrote "
" I wonder why both have same stated FS accuracy."
I think the answer could be that they just thought it up from nowhere.

 

[paulmars]

mount it inclined 10:1 for 10 times the resolution. https://www.amazon.com/dp/B0038QHTK2/?tag=pfamazon01-20

its graduated at 0.25 intervals and you can easily judge 1/5 of that. So, 0.25 included 10:1 the 0.25 would then be 0.025 and I could fairly accurately judge 1/5 of that or 0.005.

thoughts?

 

[sophiecentaur]

mount it inclined 10:1 for 10 times the resolution. https://www.amazon.com/dp/B0038QHTK2/?tag=pfamazon01-20

its graduated at 0.25 intervals and you can easily judge 1/5 of that. So, 0.25 included 10:1 the 0.25 would then be 0.025 and I could fairly accurately judge 1/5 of that or 0.005.

thoughts?

That will magnify the scale but its accuracy will depend on things like the bore being parallel with the sides and distortion through the glass sides at an angle. (And thickness of the glass)
I ask again where you got the information about the required accuracy. Or was it just the claimed accuracy of a recommended instrument? Those are two different things. I am sure you are worrying needlessly about this.