So, our final calibration procedure consists of adjusting R1 to give a meter reading of about three quarters full scale with an average emission tube plugged into the 612. I used an average emission 6L6 to calibrate my 612, as I was taught to do it that way, but I don't know of any particular reason why you should not use another tube type. So I've been without a working scale forEVER it wasn't calibrated and didn't work day one. Been randomly searching for this answer online for months, and ended up having to brush up with a quick science course! Calibrating the scale with weigh ticket from bulk tanker driver after loading: 1. With the spreader loaded and the meter turned on, press the CAL button once. The 'Cal', 'Lock', and Channel 'A' lights should be lit. The screen should show the initial calibration number of 2050. Press the CAL button again. Many states require that any scale used to buy or sell based on weight must be NTEP-approved and inspected and certified as to its accuracy. Normally, we recommend calibration every quarter by a trained scale technician with certified test weights. There are several factors to consider when deciding on frequency of scale calibration testing. I'll vouch for puzzler's method. I had to calibrate some scales for work using a standard weight. Just for kicks I compared to a stack of quarters and found that 5 quarters do indeed weigh 1.00 ounce. Didn't know dimes followed the same rule, but I don't weigh my spare change that often.
(Image from: Asuki WeighingSystem Inc.)
Nothing lasts forever, not even the highest quality and heavyduty floor scale you have. Weigh and tear occur over time and accuracy isinevitably affected. However, you can stop your weighing system from degradingeven quicker with just one procedure: calibration.
What is calibration?
Calibration is a vital procedure for heavy duty floor scalesto maintain accuracy and durability. The whole process involves a series oftests to troubleshoot the whole weighing system, determine potentialadjustments, and apply necessary repairs.
How Calibration Is Done:
·Weighing Scale Preparation (determining technicalcharacteristics and observing the overall durability of the product)
·Eccentricity Test (checking how accurate theload cells are with regards to the location of the load on the floor scale)
·Repeatability Test (preventing inaccuratemeasurements and repeatability issues when weighing loads of the same weight)
·Weighing Test (testing the accuracy of the instrumentthroughout its whole weighing capability)
·Minimum Weight Test (finding the smallest loadthat can be measured while still fulfilling accuracy requirements)
·Other Tests (might include but not limited toTare, Discrimination, Variation Indication, and Magnetic Interaction Tests)
Why do you need to calibrate?
Say you're measuring your products with an inaccurate floorscale and end up packing more than your desired measurement, that negligence cancost you and your business a huge amount of money in the long run. It'sessential to calibrate your heavy duty floor scale to increase cost savings,maintain the integrity of your weighing system, measure safely, and adhere tolocal and global regulations. With routine scale calibration and adjustments, youallow your floor scale to measure with the highest reliability while alsoextending the equipment's life.
Where to calibrate?
There are several calibration facilities nationwide but wehighly suggest you calibrate your weighing system with the help of youroriginal floor scale provider as they know your equipment too well. Forexample, you've got your heavy duty floor scale from Asuki Weighing System Inc.,you can easily contact them and avail their service that includes thoroughcalibration procedures, easy-to-read certificates, and audit-proofdocumentation.
When and how often you should calibrate your floor scale?
As per experts, floor scales must be calibrated once perquarter. That's equivalent to four times a year. There are also common signsthat you need repair, adjustment, and maintenance services for your weighingsystem as soon as possible. These are the following:
- Unable to read weight (always giving a readingof zero even if there's a load)
- Reading fluctuations (the reading never settlesdown to a consistent number)
- Repeatability issues (provides the same readingeven with different weights)
- Load cell irregularities (the reading changesdepending on where you place the load)
- Damaged parts (noticeable damages on thematerial, load cells, and indicator)
Conclusion:
Calibration is not a process that can be done once and then forgotten.It's that one simple procedure that makes a big difference in preserving yourweighing equipment and ensuring its accuracy at all times. If you rely on a heavyduty floor scale at any part of your business, do not skip routine calibration,adjustments, and maintenance for the best results.
Weighing scales, weighing instruments, weighing balances… different resources are using different terminology. I will be mainly using the term 'weighing instrument' in this article.
Weighing instruments/scales/balances, are widely used in industry for various measurements. Some weighing instruments are small laboratory instruments measuring a few grams and are very accurate. While some industrial weighing instruments are very large ones that measure, for example, mass of trucks. We all see weighing instruments in our everyday life around us, for instance, when we visit a grocery store and weigh vegetables.
As with any measurement instruments, weighing instruments should also be calibrated regularly to assure that they are measuring correctly and accurately. A proper metrologically traceable calibration is the only way to know how accurately weighing instruments are measuring.
Many weighing instruments are used for legal measurements or measurements used as basis for monetary transfer and these are part of a legal or statutory verification program based on legislation. Often the calibration of weighing instruments is based on a quality system (such as ISO9000), health care, traffic (air, marine) safety or forensic investigation.
There are dedicated regulations for weighing instruments and their calibration (EURAMET Calibration Guide, NIST Handbook 44, OIML); more on those later in the article.
In this article, the main focus is to look at the practical considerations and the different tests you should perform when calibrating your weighing instruments.
Calibrating weighing scales/instruments
Let's start by looking at some of the preparations you should make before the calibration and then look at the different tests you should be doing. Samsung j7 2016 usb driver.
1. Preparations before calibration
Before you can start the calibration of the weighing instrument, you should clarify a few things and get prepared.
You should find out the technical characteristics of the weighing instrument (max weight, d value), the accuracy requirement (max error allowed and uncertainty) and what to do if the calibration fails (adjustment).
Typically, the whole measurement range is calibrated and the calibration is performed in the location where the instrument is being used. Make sure you have enough weights for the calibration procedure available.
The weighing instrument should be switched on at least 30 minutes before the calibration. The temperature of the weights should be stabilized to the same temperature where the calibration is to be done.
The weighing instrument should be at a horizontal level, especially for small and accurate weighing instruments. Perform a few pre-tests by placing weights close to the maximum of the range on the instrument and to ensure it works normally.
In case the weighing instrument fails in calibration and it is adjusted, you should make an 'as found' calibration before adjustment and an 'as left' calibration after adjustment.
Next, let's take a look at the different tests that should be done during the calibration.
2. Eccentricity test
In normal use of a weighing instrument the load is not always placed perfectly on the center of the load receptor. Sometimes the results of a weighing instrument can vary slightly depending if the load is placed in different locations on the load receptor. In order to test how much effect the location of the load has, the eccentricity test is performed.
In the eccentricity test, the reference load is placed in a few different specified locations on the load receptor. First, the load is placed in the center of the load receptor (the load's center of gravity) and the result is observed. Next, the load is placed in four different sectors of the load receptor, as illustrated in the picture below.
The above picture is for rectangular and round load receptors, but naturally in practice there are many different shapes of load receptors and the location of the load will vary. Standards OIML R76 and EN 45501 will give guidance for different load receptor shapes.
The calibration procedure should specify where to place the load during the test and calibration results (in certificate format) should also document the locations.
The test load used in an eccentricity test should be at least one third (1/3) of the max load of the weighing instrument. The test should preferably be done using just one test load, if possible. That way it is easier to be sure that the load's center of gravity is in the specified location. For a weighing instrument with multiple ranges, the eccentricity test should be done with the highest range.
As the aim of the eccentricity test is to find out the difference caused by the location of the load, it is not necessary to have an accurate calibrated load. It is naturally important to use the same load through the test.
If the eccentricity test is used also to determine the errors of the indication, then a calibrated load should be used.
Procedure for the eccentricity test
The indication is zeroed before the test. The test load is placed to location 1 and indication is recorded. The test load is then moved to location 2 to 5 and indication is recorded in each location. Finally, the test load is placed again to location 1 to check that the indication has not drifted from the earlier indication in location 1.
The zero may be checked between each location to see that it has not changed. If necessary, the instrument can be zeroed in between each test.
Alternatively, you may also tare the instrument when the load is in location number 1, as this makes it easier to see any difference between locations.
3. Repeatability test
As any instrument, also weighing instruments may suffer from repeatability issues. This means that when the same load is measured several times, the result is not always exactly the same. To find out the repeatability of the instrument, a repeatability test is done.
The repeatability test is performed by replacing the same load on the same place on load receptor (to avoid any eccentricity error) multiple times. Test should be done in identical and constant conditions and with identical handling.
The load used should be close to the maximum load of the instrument. Often a repeatability test is done with one load only, but it can be done also with several different load values separately.
The load does not necessarily need to be a calibrated load, as the aim is to find out the repeatability. If possible, the load used should be a single load (not several small loads).
A repeatability test is normally done by repeating the measurement at least 5 times in row. For instruments with a high range (over 100 kg / 220 lbs), it should be done at least 3 times.
In the repeatability test, the instrument is first zeroed, then the load is placed on load receptor and indication is recorded once it is stabilized. Then the load is removed and zero indication is checked and zeroed if necessary. Then the load is placed again, and so on.
For a multi-range instrument, a load close but below the first range max is often sufficient.
4. Weighing test
The purpose of the weighing test is to test the accuracy (calibrate) of the weighing instrument throughout its whole range in several steps, with increasing and decreasing weight.
The most common practice is the following: start with zeroing the instrument without any load. Set the loads of the first test point, wait for stabilization, and record the indication. Continue increasing the loads through all the increasing test points. Once the maximum load is recorded, start decreasing the loads through the decreasing test points.
In some cases, the weighing instrument may be calibrated with increasing loads only or decreasing loads only. Typically, 5 to 10 different loads (test points) are used. The highest load should be close to the maximum of the instrument. The smallest test load can be 10% of the maximum load, or the smallest weight normally used.
Generally, the test points are selected so that they are equally distributed throughout the range. More test points can be used for the typical range of usage of the instrument.
With multi-range instruments, each range is to be calibrated separately.
Linearity
In a weighing test, using multiple points through the measurement range of the instrument helps to reveal any issues with linearity. Linearity issues means that the instrument does not measure equally accurate throughout the range. Even the zero and full span are correct, there may be errors in the middle of the range, which is referred as linearity errors, or unlinearity (or nonlinearity).
Below picture is a general illustration of unlinearity. Even instrument's zero and full range are adjusted correctly, there is error in the midrange due to unlinearity of the instrument:
Hysteresis
Hysteresis is the difference in the indication when a test point is approached with increasing or decreasing weight. To find out any hysteresis issues in the instrument, you need to calibrate with increasing and decreasing points.
In a weighing test, when increasing or decreasing the load, it is important not to overshoot or undershoot. This means that when you increase the load, you must approach each test point with increasing weight. You should not add too much weight and then remove it, because then you lose the hysteresis information.
Likewise, with decreasing points, make sure that you approach each point with decreasing weight. Obviously, in order to be able do this, the usage of the test loads should be well planned in advance.
Picture below is a general illustration of hysteresis. When instrument is calibrated, the results are different with increasing and decreasing calibration points:
5. Minimum weight test
Minimum weight test is a test that is not always required to be done. This test is anyhow required within some industries, like the pharmaceutical industry. Air traffic controller 3 download full version windows 7.
The purpose of the minimum weight test is to find the smallest load that can be measured while still achieving reliable measurement results and fulfilling the accuracy requirements. When the measured value gets smaller, typically the relative error of the reading becomes higher. The weighing instrument should not be used to measure any loads smaller than the minimum load.
For the minimum weight test, the two main standards have different approach. Let's take a quick look of those:
The US Pharmacopeia (Chapter 41)
- After the recent changes in the standard it does not refer to a minimum weigh test anymore, this has been replaced by the requirement to determinate the instrument's minimum operating range by finding the point where the instrument's repeatability (2 times standard deviation) is 0.10% of reading.
In practice, in some cases the standard deviation can be very small, but the minimum weight to be measured should anyhow not be smaller than 820 times the actual scale interval (d).
EURAMET Calibration Guide 18 (Appendix G)
- Has the principle that you calculate the measurement uncertainty for each calibration point and the smallest usable load is the point where the uncertainty is still small enough for the requirements for the instrument.
In addition to the above standard requirements, the requirements in the pharmaceutical industry requires a separate minimum weighing test, where a small test load is measured multiple times to find out the accuracy of the instrument with a small load.
6. Other tests
There are also some other tests specified in the standards, although these are typically not done during a normal calibration, but can be done as a type of approval test or in the initial verification.
Example of these tests are:
- Tare test
- Discrimination test
- Variation of indication over time
- Test of magnetic interaction
Additional topics in the related white paper
To avoid this blog post to come way too long, please download the related white paper to read more on this subject. The white paper discusses following additional subjects:
Weights
- Handling of weights
- Nominal mass / Conventional mass
- Calibration of weights
- Local gravity
- Air buoyancy
- Effect of convection
- Substitution load
Calibrate Scale With Quarters For Sale
Calibration certificate
- What information should the calibration certificate include.
Uncertainty
- What kind of things will cause uncertainty in the calibration of weighing instruments?
Instrument classes, Tolerance classes, Max permissible error
Written by
Heikki Laurila is Product Marketing Manager at Beamex Oy Ab. He started working for Beamex in 1988 and has, during his years at Beamex, worked in production, the service department, the calibration laboratory, as quality manager and as product manager. Heikki has a Bachelor's degree in Science. Heikki's family consists of himself, his wife and their four children. In his spare time he enjoys playing the guitar.
Calibrate Scales With Coins
Related references
How To Calibrate Gram Scale
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- EURAMET Calibration Guide No. 18, Version 4.0 (11/2015)
- EN 45501:2015 – Metrological aspects of non-automatic weighing instruments
- NIST Handbook 44 (2017 Edition) – Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices
- U.S. Pharmacopeia Convention 'Chapter 41 Balances' (2014) (abbreviation 'USP 41' used in blog text)
- EA-4/02 (2013) – Evaluation of the Uncertainty of Measurement in Calibration
- JCGM 100:2008 – Evaluation of measurement data — Guide to the expression of uncertainty in measurement
- JCGM 200:2008 – International vocabulary of metrology — Basic and general concepts and associated terms
- OIML R76-1 – Non-automatic weighing instruments Part 1: Metrological and technical requirements – Tests
- OIML R 111 – OIML R111: Weights of classes E1, E2, F1, F2, M1, M1-2, M2, M2-3 and M3
- DIRECTIVE 2009/23/EC (2009) – Non-automatic weighing instruments
