Weighing Basics

Weighing Basics

  • Submitted By: Rupak
  • Date Submitted: 10/09/2009 11:58 AM
  • Category: Technology
  • Words: 4629
  • Page: 19
  • Views: 381

Calibration Weights, Frequently Asked Questions
Q. I did the "auto calibration" on the analytical balance. But when I check it with my weight, it still isn't right. I know my weight is accurate, since its class 1, and we just had it calibrated. What can the problem be?

A. Your weight is erroneous, even though it's just been calibrated. Class 1 weights have errors just like all other weights, and those errors are easily measured on an analytical balance. The following table shows the nominal value, and both the high and low limits of class 1 weights Nominal Value g 10,000 5000 2000 1000 500 200 100 Maximum ASTM 1 10,000.02500 5,000.01250 2,000.00500 1,000.00250 500.00125 200.00050 100.00025 Minimum ASTM class 1 9,999.97500 4,999.98750 1,999.99500 999.99750 499.99875 199.99950 99.99975

that it is within class 1 tolerance. It WOULD BE a certificate that says what the actual weight value is – gives you a number. If you are buying calibration services for your weights, be sure you understand the difference between a certificate that simply says the weight is in tolerance, and a calibration report that tells you precisely what the actual value of the weight is.
Q. What if I don't have a calibration certificate for my weight?

For example, the 100 gram weight can be as much as 100.00025 gram, and as low as 99.99975 gram , and still be within ASTM class 1 (formerly class S) tolerance. A standard analytical balance reads out to four decimal places. If we round the maximum and minimum to four decimal places, then the maximum reading is 100.0003, and the minimum is 99.9998. So any reading in this range is possible on a "perfect" analytical balance. Of course, if the instrument has any errors (they all do), then those are additional.
Q. Wait a minute! Are you saying my class 1 weights aren't good enough?

A. Right. An ordinary analytical balance is MORE accurate than those weights, and it will readout (measure) the difference between the internal calibration...

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