Re: Scales & Balances (was APD V5 #383)

[George Slusarczuk <yurko at warwick_net>]

Hello James,

To keep their accuracy, electronic (digital) balances have to be
calibrated frequently. An electronic analytical balance has to be
calibrated at least daily. If you have a "standard weight" it's not much
of a chore, but a chore nevertheless. If you are NOT doing many
weighings each day, the convenience of an electronic balance is not such
an advantage.

A mechanical balance generally holds its calibration forever. It takes a
bit longer to weigh something on it, but if you average only 1 or 2
wighings a day, it just does not matter.

You probably need only 0.1 g accuracy, BUT a "0.1 g sensitivity" does
NOT guarantee you a 0.1 g accuracy! With a 0.01 g sensitivity on a
reasonable quality mechanical balance (Ohaus is such a brand) you are
fairly certain of 0.1 g accuracy.

Thus I would recommend the 310 g capacity Ohaus balance. (I own one.) It
will be suitable for 99.9 % of a hobbyist's requirements!

Best,

George 



> 
> Back in February of 2001, Chuck Gadd was wondering about how he could obtain
> more accuracy in dosing certain nutrients. In response to his question,
> Roger Miller wrote the following:
> 
> "The best procedure is to get (beg/borrow/buy) a reasonably accurate
> scale and measure the weight and volume of the chemicals you use under
> your conditions.  That isn't a real satisfying alternative for most
> people, but I think it's the only solution that will make your
> calculations reasonably accurate."
> 
> O.K., I don't have access to a University/Research Lab with an analytical
> balance, but I do have a web browser and a credit card (oh no, not the
> credit card again!). I've been considering buying a balance and from
> searching the web, it seems that my choice is to get either a mechanical
> beam balance or a digital scale, probably one designed for use by jewellers
> (small size and precision).
> 
> I have narrowed down the search to the following models:
> Mechanical -
> Ohaus Triple Beam, capacity of 610 g with a sensitivity of 0.1 g
> Ohaus Cent-O-Gram, capacity of 310 g with a sensitivity of 0.01 g
> Digital -
> iBalance 101, capacity of 100 g with a sensitivity of 0.01 g
> MyWeight MX-50, capacity of 50 g with a sensitivity of 0.01 g
> MyWeight Flipscale 125, capacity of 125 g with a sensitivity of 0.05 g
> MyWeight Flipscale 350, capacity of 350 g with a sensitivity of 0.1 g
> 
> Now, to my questions - does anyone have any opinions as to the relative
> accuracy of a mechanical balance such as either of the Ohaus models and a
> small digital balance. Is one to be preferred over the other on the basis of
> absolute accuracy?
> 
> - - how much precision is required? Is a sensitivity of 0.1 g enough or should
> I pop for a model that can read to 0.01 g?
> 
> I'm REALLY tired of tablespoons, teaspoons, etc. and would like to know what
> I'm putting into my tanks with more precision.
> 
> Thanks,
> 
> James Purchase
> Toronto