What You Need to Know about Meter Calibration


In this issue and the next issue, we’d like to discuss the various aspects of meeting customer’s needs concerning meter calibration. Have you received questions from your customers concerning ISO 9000, and the accuracy of the customer’s meters? It’s possible you may be asked just to calibrate meters so that the customer knows their meters are accurate. Or, your customer may be concerned with ISO 9000 certification. The purpose of ISO 9000 standards is to ensure that customers purchase products that are designed, built, tested, and sold under controlled conditions by trained people. Any customer, whether they represent a small company or a large multinational company, minimizes their purchasing risk by dealing with internationally recognized, ISO 9000 registered suppliers. ISO 9000 audits are concerned with the documentation that businesses have, and whether they are following that documentation in their work procedures. It’s up to the business to be responsible for the step-by-step procedures of their documentation. Providing meter calibration services can be easier than you think, and the goal of these articles is to help you provide this service to your customers. We’ll begin by laying some of the groundwork to help understand what we are trying to accomplish with meter calibration. Four topics will be covered
at this time:
1. Calibration vs. Certification
2. How often is calibration necessary?
3. Resistive load vs. a welding arc
4. Calibration Equipment Source

Calibration vs. Certification

When you calibrate a meter, you are simply verifying that the meter is accurate within tolerances, and if not, you adjust it to make it accurate. Certifying the meter means supplying a “paper trail” showing that the calibrated meter can now be traced back to the National Institute of Standards and Technology (NIST), through your testing equipment. This simply means that you need a source to certify your meter also. How often is calibration necessary? When do you calibrate the customer’s machine meters? We recommend every year, hopefully combined with a preventive maintenance package. Remember that for the procedures for ISO 9000, you can make this interval any time period you want. The actual procedures made for ISO 9000 documentation can come from a couple of sources: the customer could give you the procedure, they may ask you to provide a procedure, or you may work on the procedure together with the customer.

What You Need to Know about Meter Calibration

In an article to follow, we will provide a sample procedure form that can be used as a guideline. The “bottom line” with a procedure is – make sure you do what you say you are doing in the procedure. (If you say you are going to test the meters every two years, make sure you have a system in place to remind you when two years are up.) Also keep in mind that the time interval you and your customer develop can be changed. For example, if you find that the meters are staying accurate and don’t need to be adjusted year after year, there is nothing wrong with extending the meter calibration interval to every two years. And the opposite is also true, that if the meters are needing calibration more often, you can change the interval to every six months. Resistive load vs. a welding arc A welding arc is often referred to as a dynamic load, which simply means it is a changing load. Therefore, do not calibrate meters while welding. We strongly recommend using a resistive (constant) load. Both Miller Load Banks are excellent examples of resistive loads. The LBP-350 Portable Load Bank was specifically designed to help you calibrate meters in the field. (It weighs only 46 pounds.)

Calibration Equipment Source

Some of you may already have a company that you purchase your calibration equipment from, and that’s fine. If you do not have such a company, we’d like to introduce you to Transcat, a company that we are very familiar with. Transcat calibrates and services all brands of calibration, test, and measurement instruments. They are headquartered in Rochester, New York, and have many locations across the nation.

They can be reached at:
Phone: 800-828-1470, or 716-352-9460
FAX: 800-395-0543, or 716-352-1486
Website: www.transcat.com
E-mail: info@transcat.com

Transcat not only sells test equipment, but will also supply you with the “paper trail” you need for your testing equipment certification. Transcat can also calibrate your previously owned test equipment. We also can recommend a source, Q-Cee’s Products Division, that can supply you with the actual stickers you apply to the meters. These stickers will have places for you to fill in the information needed, such
as the date calibrated, due date for the next calibration, and the calibrating person’s identification. QCee’s is located in Houston, Texas, and can be contacted by phone at 800-950-4922, or 707-575-3524.

Editor’s Note: Hopefully this first article raised your interest in calibrating and certifying welding equipment. In the next issue of TechLine, we will go into more detail on calibration test equipment, and we will provide information on a sample calibration procedure. If you have questions on the information provided here so far, or something else you’d like to see in TechLine, please don’t hesitate to drop us a fax at TechLine, 920-735-4013. We appreciate your input!

Warning: When working on welding equipment, follow all safety precautions in the Owner’s and Technical Manuals. Have only qualified service technicians calibrate welding equipment.

In this follow-up article on meter calibration and certification, we want to show you a sample procedure you might follow. Please locate the insert page and keep it handy, as we’ll be referring to it. Let’s say for example that your customer has asked you to calibrate/certify their Miller CP- 302 welding power source. You have also been

provided with a procedure written by their Quality Assurance department. (See #1 on insert.) At this time, read Steps A & B. We have filled out a sample sheet for Step B – Ammeter.

To calculate the percentage of error, follow this example from the Calibration Data Sheet (#2 on insert):
300 – 289.7 = 10.3
10.3 300 = .034333 = 3.4%

In Step “C” fill out the Certificate of Calibration (see #3 on insert). Add a sticker to the CP-302, fill out the paperwork, and you’re done!

We’ll cover more on calibration in future TechLines, but we’d like your input as to what issues about calibration concern you. Why not drop us a line on our fax machine? Contact us at: FAX 920-735-4013. Let us know what you think about this calibration information so far, and what else we can cover that would be of value to you. Thanks!

A. Voltmeter Certification
1. Voltage readings shall be taken at the output studs of unit under test. Voltage readings shall be taken at open circuit
voltage with the Fluke 45.
2. Verify that welder voltmeter reading is within + or – 10% of standard meter reading. (If adjustment is required, see
technical manual for each make and model.)
3. Take readings at 10 volt intervals from min to max open circuit voltage.
4. Record data on a Calibration Data Sheet (Form #686-8/99).

B. Ammeter Certification
1. Put certified shunt in series with Miller Load Bank #043329 and the output of unit under test.
2. Monitor output of shunt with Fluke 45.
3. Verify that welder ammeter reading is within + or – 10% of standard meter reading. (If adjustment is required, see
technical manual for each make and model.)
4. Take readings at 100 amp intervals from 100 amps to max amperage output of unit under test.
5. Record data on a Certification Calibration Data Sheet (Form #686-8/99).

C. Certificate
1. Fill out Certificate of Calibration form #189-3/99.
2. Fill out a Certification sticker. Place sticker on front panel of unit under test.
3. Customer receives the original Certificate of Calibration.
4. File a copy of the Certificate, along with a copy of the order inquiry, and all of the completed data sheets.