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Discussion in 'B&W: Film, Paper, Chemistry' started by patrickjames, Dec 8, 2006.
Can anyone recommend a good place to get a chemistry scale and a good one to buy?
Do a search, there are a few good threads about it, but I use a mechanical scale, an Ohaus triple beam balance, good for up to 2610 grams (with extra weights), with an accuracy of 0.1 gram. Mine is without the extra weights, so it works to 610 grams. Others may have other preferences.
I just got this:
Item Name: Acculab EC-211 Portable Scale [210g x 0.1g]
Item Number: EC211
or maybe this one would do - I'm not sure how big it is:
I'm using an older version of that - up to 200g, 0.1g precision. It works - and works well enough for darkroom use.
I have a little digital pocket scale. 200 grams, accurate to +/- 0.1 gram. 200 is fine for small formulas, but if I got another one, I'd want it capable of up to 500 grams.
Oh, you do get what you pay for. I had a cheap digital model which had sensitivity all over the place while it just sat there. 63 grams, no, 62. No, 65. Wait, 61. Grrrr. Look for a model with a calibration weight included - those are nice to check accuracy.
I've an Acculab from five years ago and working
perfectly. I've found it's 200 gram capacity, .01 gram
resolution and accuracy a best combination. That many
grams will see you through just about any full liter of stock
or concentrate you will likely ever come across. The .01
gram resolution will handle those very small amounts of
this or that often encountered. Also very nice to have
when experimenting or working with less than full
amounts when preparing fractional batches. Dan
I was able to get an Ohaus tipple-beam scale on ebay for $25 in good shape, bit it took a little patience. They can be had for a bit more any dey of the week though if you want one now. Personally, I prefer the mechanical scale, but there are good digital scales out there.
A scale used by those who load cartridges can be had at sporting good shops. Some will have both the gram scales and the grain scales. A gram is 15.28 grains IIRC. The capacity is not great, but is enough for most of the chemicals that need accurate weighing. These are usually balances. Larger amounts can be weighed with sufficient precision on kitchen spring scales.
You have discovered from a previous post the difference between accuracy and precision. A scale may read to 0.001 grams but not be accurate to 1 gram.
Pat, still remember that one from school. Accuracy is hitting the x-ring one time. Precision is being able to do it every time. I bought an Ohaus tripple beam balance (new) on the internet from a scale dealer a few years back. It is the stripped down model without weights, but it works well enough for my use. I think it was about $85 with shipping.
I was surprised to see how many digital scales were out there, and how few were analog types. Being middle age, I chose the older type and have been happy ever since. Nice to use one which you can actually see the amounts on a scale. My powder measure won't go up as far as I need at times. Don't usually reload for artillery, largest is just the puny 375 H&H. tim
I have an Australian version of the Ohaus triple beam which is capable of 610g or 2610 with the extra weights.
I bought it new about 15 years ago, was a brilliant decision.
Recently with my business, I bought another process which required measuring to 0.01gm accuracy. Well the process came with electronic scales and my first thought was that I could use these for photographic chemicals.
This I duly did, but after using them for about three months, I went back to the analogue scales. I cannot explain why, but the analogue scales are more user friendly, even if I have to screw the superfine adjuster in or out to zero in, for each plastic measuring cup I use.
I think it comes down to the way one can tap, tap the measuring spoon slightly, allowing more chemicals to drop and at the same time, watch the sway of the beam as it gets closer and closer to zero.
I have an Escali Liberta that I bought cheap on eBay. It's got a capacity of 100g, a precision of 0.05g, and the accuracy seems OK (at least, it consistently gives me the same reading when I weigh the same object). It comes with a 50g calibration weight. I fully expect it'll die sooner than would a more expensive model. If I were doing it again, I'd probably go one of two routes:
Buy two cheap scales: One with 0.01g precision and (probably) 50g or less capacity and a second with 1g or coarser precision and a capacity of over 100g.
Buy a more expensive scale with 0.01g precision and 100g or greater capacity.
In cheap scales, as precision improves (that is, goes to smaller numbers), the capacity goes down, and vice-versa. The problem is that when mixing photochemistry, you sometimes need to measure large quantities of stuff (say, sodium thiosulfate for a fixer), but you don't generally need great precision when making such measurements; and other times you need to measure small quantities (say, small fractions of a gram of phenidone for some developers) with high precision. Thus, a single cheap scale won't do a good job unless you split up the big stuff into multiple batches, create percentage solutions of the small stuff, or both. The Escali scale I bought is something of a compromise, with its peculiar 0.05g precision and 100g capacity, but I think two scales or a single more expensive and capable scale would do better.
I bought an Ohaus on eBay. Looked great in the picture. Description was 'excellent'. It's basically a $30 paper weight. Needs service. The service will come close to what a new scale would cost. Avoid the temptation of buying a used mechanical scale on eBay. I believe that that is a hit or miss proposition, and the money is better spent on a new scale from a reputable dealer.
Weighing precision in photography is rarely needed. And most of the scales floating around are "consumer" scales with enough accuracy - pick up a test weight (200g) does not need to be certified.
I sell scales for a living - all of them would be overkill for photography. An old mechanical would also be fine. Understand that a "good" load cell is at least $70 - that is the heart of the scale. Then put a cabinet around it and electronics to do the conversion and then the math ... a decent industrial commercial scale is at least $750. The costly items are a good 24bit a/d chip and the buffering and protection around it. A good power supply - any fluctuation in voltage will reduce accuracy. And don't forget good software, which includes Finite Infinate Response filtering - and linearization - none of these come on the calculator chip used in the cheap scales I see floating around. So know you know more than you ever needed to know about scales - and it doesn't really matter.
The scale I use retails for $800, it is a 500g scale at .01g displayed resolution with a million internal counts of resolution and an on board database for recipes. Very cool. I can weigh my phenidone for small batches. There is better yet .. a lab balance - we have a pill counter at 310g with .001g resolution and a database. It uses forced restoration technology to do the weighment. At $3100, way overkill - We sold 6,000 last year.
I believe that what you're trying to say here is that we don't need precision as much as repeatability. And that even in that we have a pretty large margin of error, so that basically any scales which can weigh a small enough amount is very likely to be "good enough"?
In my experience, keeping things within a 10% margin of error is overkill.
Just curious: what was the problem with it? They look kind of foolproof, but I am no expert on scales...
If I calibrate the scale with a known weight, and then weigh another item with a known weight to test it, the second item doesn't weigh the correct amount. And if I recalibrate with the second item and go back to the first, or to a third item with a known weight, again the scale is 'off'.
It's not at all consistent.
If anyone has suggestions on what to do with it besides sending it into Ohaus for overhaul, I am all ears.
Thanks Neal, I've never thought of it that way - I will have to check mine in the same manner, just to be sure. I also bought mine secondhand.
I used to measure powders at the post office, then I almost got arrested! That's when I switched to liquid concentrates.
And to the practised user, the beam doesn't have to settle down for most measurements. One can judge the center of its swing quite well, especially when the beam has some inertia and consequently a fairly long period to the swings, and some degree of damping of the motion due to the size of it and the consequent air drag.
I already had a letter scale accurate to 1 gram so I bought a cheap digital 0.1g accuracy scale. Weigh large stuff on the letter scale and small, more precise, amounts on the pocket scale.
Is any body using this scale? Acculab VIC-212 Laboratory Balance 210g x 0.01g
Thank You for your help.
I've a V-200 0.01 x 200 bought new six
years ago. Very pleased. Dan
I use an Ohaus Centigram scale I purchased at a flea market, had to get a new pan and recalibrate it for zero. But its a great scale, weighs to 0.01g and a total of 311g. You don't need good precision often, unless you're weighting phenidone.
Maybe something to do with (my young) age, but I'd kill myself if I were to measure anything on a beam balance repeatedly.
Digital scales give the reading in 5 seconds or less and you don't see the rocking of the beam back and forth.
I find it useful to have two scales. One for loading shotgun shells used every day to mix paper developer. One very nice expensive scale from a scientific supply store for measuring film developer and platinum chemistry. Using the scales everyday for paper developer it gets pretty groady and it is nice to dedicate that for one use.