Saturday, 9 April 2011
Pocket Scale - portable, chemistry
I needed a scale that could measure quantities less than 10mg and did not want to buy a $1500 piece of lab equipment. If you are careful and consistent with your measuring techniques, this scale is repeatable to within a few milligrams - often to its finest resolution of 0.001g. These are essential for this performance: 1) let the scale stabilize on a hard, flat and level surface. 2) Make sure the sample tray is properly seated inside the circular detent of the scale's metal measuring platform. If you're not careful, the sample tray (as provided) can touch the body of the scale, grossly throwing off the measurement. I glued a small piece of metal to the bottom of the sample tray raising it higher for more clearance. I'll often tap the table that the scale is on to help everything settle. 3) calibrate as described in the manual. 4) place and remove samples consistently and carefully - don't drop them. Even the slightest impact can throw off the measurement. 5) wait for ten seconds or so for the sample to settle. 6) for minuscule samples, use the ten gram weight in addition to the sample to put the scale in the middle of its operating range. With a little care, one will get closer to the performance of a lab-grade milligram scale than anything else for this price. Nice scale.
I was hesitant to buy this given the review indicating that there may be a problem with the power supply to this scale. However, I was hoping that the other reviewer's case may have been isolated given the vast number of scales that AWS offered.
I've been using mine for about two weeks, making sure to turn it on and weigh the calibration weight at least once a day to check a) the power to the scale, and b) the accuracy of the scale over a period of time checking for consistency.
I can say that mine doesn't have an issue with eating away at the batteries and the scale is always within a 3mg error range of the 10g weight (usually less). I would say given the cost, that it is an extremely accurate and affordable scale.
I'm amazed that you get a balance which can display to the nearest milligram for the price that I would expect to pay just for the two calibration weights, which are included. Unless you've had a course in analytical chemistry or work in a lab where precision weighings are routine, here are a few tips. Do keep in mind that it is a precision instrument - use a light touch adding weight to the pan, always use the tweezers -- do not touch the pan or weights with your bare fingers. Keep the balance in a clean environment away from fumes, and only use it on a solid vibration free surface. For precise weightings to the nearest milligram, don't lean on the table, which must be solid, level, and vibration free. This balance is a little gem and an incredible bargain.
I bought this sale for measuring spices for cooking. My kitchen scale had a 2 g resolution, and 1/4 teaspoon of salt is 1.5 g, so it was inadequate. The photos of this product are misleading, the scale is tiny! About half the size it looks in the pictures. I added a picture of the scale with a dime and a ruler to give a better idea of its size.
The construction of this scale leaves a bit to be desired. The aluminum plate that covers the area around the sensor is attached with double sided foam tape, and was slightly warped, so it had sprung away from the tape to the point where it would make contact with the tray, throwing off measurements. Once I got the aluminum plate flat and stuck to the tape, I found that the measuring trays bottom does not quite match the dimple in the sensor, so it does not sit solidly on the sensor.
This scale is less than ideal for my purpose. The measuring tray is only 1.3" in diameter, much too small to catch all of the pepper from a pepper mill, and there is a gap between the sensor and the aluminum plate that would allow crud to fall inside the unit. The ideal scale would have a measuring plate that covered the entire top surface, and an overhanging lip so that spills would land on the table, and not inside the scale. I think that I can make an alternate tray using a sheet of plastic and a toothpaste tube cap that will allow me to use this scale for my intended purpose.
Things that should have been mentioned in the description of this product:
This scale can measure using the following units: g (gram), oz (ounce), ozt (troy ounce), dwt (pennyweight), ct (carat), gn (grain)
This product gets 4 stars because it does what it is intended to do and is cheap, it looses one star because of sloppy construction.
The pan for the scale, which is essential to using it, did not have a deep enough indent, thus the side of the pan hit the edge, causing inaccurate weighing. if the load was slightly off center, the weight would be low. Fixed it by putting a dime inbetween the pan and the weighing surface. now it works well, but I always need a dime. - Balance - Accurate - Pocket Scale - Portable - Digital - Chemistry'
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