Proposed Rule: Mandatory Reporting of Greenhouse Gas Emissions 

Meeting Documentation 

Date Staff Contact 

Information (Name, email, phone #) 

Name of Organization (Attach list of all attendees names and emails if possible) 

Summary of Discussion (e.g., applicability, reporting requirements, etc.) 

Written CommenProvidedDid they submit to 

Email & telephone correspondence from 7/2/10 – 7/10/10 

 Mollie Averyt, ICF International, 202-862-1569 

maveryt@icfi.com

Paul Stewart, ICF International 202-862-1135 pstewart@icfi.com

Deborah Harris, ICF International 202-862-1574 dharris@icfi.com

on behalf of EPA under Contract EPW-07-068, Task Order 68 

Representatives from Partner Companies of EPA’s SF6 Emission Reduction Partnership for Electric Power Systems, including: Oncor, AEP, BPA Industry contacts including: Dilo, Air Products, Airgas, and NIST 

Topic: Error in cylinder weight measurements 

Questions were researched regarding: 

- whether the error of scales is typically expressed in 

absolute terms; 

- if scale manufacturers distinguish between accuracies 

and precisions; 

- precision and accuracy of the best-performing scales 

now owned by electric power systems; and 

- procedures at gas suppliers for filling cylinders and 

verifying that they contain the correct amount of gas 

In addition to telephone correspondence and e-mail, web research also conducted. Research notes provided below. 

No 
Scale Error Research Notes - 7/2/10 – 7/10/10 

1. Is error of scales typically expressed in absolute terms (e.g., percent of full-scale or 2 lbs) or in relative terms 

any level)? If precisions and accuracies are expressed in terms of full scale, what is full scale? 

Web research: Scale Manufacturers: 

1. Dilo (http://dilo.com/accessories.html) – absolute (+/- 0.1 lbs) 

2. Scaletron Industries (http://www.scaletronscales.com/) – absolute 

3. Intercomp (see attached spec sheet) - relative 4. Brooks Instruments 

(http://www.brooksinstrument.com/downloads/Product%20Documentation/Cylinder%20Scales/Data%20Sheets/gc(+/- 0.1% of full scale) 

5. Avery Weigh-Tronix (http://www.wtxweb.com/literature/drum_L.pdf) –understanding is that this is absolute (5000 

6. Tramfloc (http://www.tramfloc.com/tf57.html) – relative (some are 1% some are 0.5 % of capacity) 

It is clear that both relative and absolute terms are used. However, +/- a certain percentage of capacity (i.e., absolute) seemthrough research of various web sites of industrial scale manufacturers (that may not necessarily be targeted for SF6, althou

weighing liquefied gases such as ammonium). A +/- a certain percentage of capacity translates into an absolute term; capa

between 300 and 350 lbs (e.g., 0.1% * 349lbs = .349lbs in absolute terms). Accuracy expressed in this way may be the reaothers in the electronic industry) submitted the comment to have the accuracy expressed in absolute terms. NIST Handbook 44: It is not clear whether the NIST handbook does addresses this question; it certainly does not address i

devices are divided into accuracy classes (I, II, III, III L, or IIII) according to the number of scale divisions (n) and the valu

(d). Table 3 provides n and d for each class. Table 7a explains each class in terms of weighing application or scale type. Cthe scale type for these industries. 

1 “Divisions” refers to the amount of increments a scale offers. The amount of divisions can be determined by taking the scale's capaci

readability (the smallest number a scale can display). http://www.balances.com/applications/glossary.html
Additional information from Steve, Cook, NIST (7/7/10):

- Tolerance is defined by NIST Handbook 44 as “A value fixing the limit of allowable error or departure from true p

- “Maintenance tolerance” applies to equipment in actual use; whereas the “acceptance tolerance” applies to equipm

commercial use for the first time (along with some other conditions, for example, equipment returned to commerciofficial rejection for failure to conform to performance requirements ,which is officially tested w/in 30 days after c

- The term “count” is synonymous with the terms “division” and “graduation”. - Scales are tested against a reference and that reference is a physical standard. This physical standard, or “value” as 

definition of tolerance, is a block of metal that is a certain weight as verified by weight and measures divisions at sgovernments. 

- An example –a scale that has a capacity of 1,000 lbs is graduated by 1lb. Therefore, if something is weighed that i

graduations. You would then go to Table 6 of handbook 44 (“Maintenance Tolerances”) 

(http://ts.nist.gov/WeightsAndMeasures/Publications/upload/2-20-09-HB44-FINAL.doc) and look up the allowabl

case is 1 graduation. 

2. Do scale manufacturers distinguish between accuracies and precisions? Repeated measurements on a scale 

decrease (improve) the precision of the summed or averaged measurements, but will not affect the accuracieaveraged measurements. 

Brooks Instruments does provide precision expressed in absolute terms (+/- 0.1% of full scale). In a brief search, precision

specification sheets from other manufacturers. BPA and Oncor (phone calls): out of all of the scales they researched, they did not see any information on precision, only 

AEP (phone call): not sure. 

Reply from Dilo (information from Cooper Instruments): “There is the overall accuracy of a load cell. This is determined b

Hysteresis, and Non-Repeatability. This is based on the full scale of the load cell I.E: 1000 lbs. So if you want to know whacan multiply an accuracy of 1% by a full scale of 1000 lbs. So you can say your precision is 1 lbs.” 
3. What is the precision and accuracy of the best-performing scales now owned by electric power systems? 

BPA (phone call): They use Dilo scales, which, from the research, appears to be best performing. 

Oncor (phone call): They use the basic scales available at retail stores such as Walmart. 

AEP (phone call): they have a scale in each of their store rooms but was not certain of accuracy. Believed that they were lo

reporting rule in mind, they are planning to have each region buy new scales. They have at least 5 store rooms – each store 

keep their gas for each of regions. There may be some scales at some substations that are 3 hours away or more. They do naround on trucks. 

4. What is procedure at gas suppliers for filling cylinders and verifying that they contain the correct amount of 

placed on a scale and filled until they reach the target weight of nominal tare + correct fill (119 lbs + 115 lbs

tare weights measured at the supplier prior to cylinder filling? 

Response from Gas Suppliers: Airgas (phone call): The former, i.e., the target weight of nominal tare + correct fill. They refer to a tare weight stamped on 

cylinder. They will know how much each cylinder can hold. They rarely fill them empty. Air Products: sent email (and followed up with a call): “I can only speak for what we do at APCI. Our competitors may do 

different. For cylinders: We get the tare weight of each cylinder prior to fill. We fill these in batches of 10 on the same manifold. We use scales fo

1 for cylinder 1, scale 2 on cylinder 2 for cylinders 2&3, Scale 3 on cylinder 4 for cylinders 4-6, scale 4 on cylinder 7 for cyexample we would fill cylinder 7 to target and then stop the fill on 7-10. After the fill on all 10 is complete, we weigh each to get the product weight. For Y Containers: Each Y has its own scale and is tared and then filled to a target weight. For ISO containers: Iso containers are filled to target weights using Temperature and Pressure readings. After they are fill

the truck scale. The are tared prior to fill. We use Metler-Toledo scales for cylinder and Y fills. Toledo truck scales for ISO fills.”