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Weather Related Organizations => CoCoRaHS => Topic started by: miraculon on February 11, 2022, 09:54:21 AM
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One of my outer cylinders that I use for CoCoRaHS has apparently changed mass over time. The original label said 459g, I re-weighed it and it shows 456g on both the Escali scale and a postal scale that I have. I am certain that my original mass measurement was correct.
I use a 500g test weight that shows 501g in the garage scale (w/heater) and the basement Escali shows it as 500g (tipping to 501g sometimes) each time I measure the snow mass.
Can the loss of plasticizers (VOC?) cause this? Has anyone else seen an apparent mass change for an empty cylinder?
Greg H.
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Hi Greg,
My scale isn't a high precision scale but it does measure in 0.5 gm increment. I have 5 outer tubes, 2 for daily precipitation catchment and 2 for replacement at 8:00 am, and the other for measuring new snow and total snow on the ground SWE. A couple are 8 years old and the most recent this fall from CoCoRaHS Canada. I got the scale before first snowfall in November and empty weighing for the 5 tubes at the time varied from 451.0 to 460.5 gm. I have continued to weigh the empty tubes after each rain and snowfall and have found that the same empty outer tube can weigh different on different days, with a +/- difference of up to 3 gm. I've only submitted the weight method SWE to CoCoRaHS for my weekly total snow on the ground where any difference is relative minor. I wait for the snow melting to submit the daily SWE.
A bigger beef is that I submit in metric and CoCoRaHS converts to Imperial in their records and then display back in metric and with the rounding then does not display nor log what I submitted - i.e. 0.6 mm becomes 0.5 mm and 26.0 mm becomes 25.9 mm, and in metric the increments are in .2s so 0.5 and 25.9 shouldn't exist.
Enjoy,
Paul
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Hmmm.. Interesting. My recent measurements of the suspect cylinder have been consistent from day-to-day. I also weigh the 500g calibration weight (https://www.amazon.com/gp/product/B01MT5G632?th=1) each time and the scales are repeatable.
It might be interesting to see if your variation is due to drift in the scale or some other factor when using a calibration weight. I picked 500g since it falls in range with a reasonable rain amount.
Thanks for the response, Paul.
Greg H.
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Hi Greg,
One thing I've noticed is that when I bring in the full cylinder and weigh it, then leave it for a while while snow is melting (I cover it to hopefully avoid evaporation) and then when snow is melted I weigh the full cylinder again and often see a 0.5 gm difference (mostly less). I've wondered if the temperature difference between just coming from outside and then leaving it inside for a while could affect the weight?!?. After the snow is melted I pour it in an inner tube to get the actual mm, and then I weigh the empty cylinder after the melt is complete.
Maybe it is my scale as it is a cheapy from CTC. I'll experiment by also weighing the cylinders before I put them outside and compare that to the empty cylinder when I bring it in the next morning. I'll also do the same for the cylinder I use to measure the new snow and the snow on the ground on Mondays as then I get two empty measurements of the same cylinder within a short period. I'll also check with another kitchen scale...
Enjoy,
Paul