S-S-06—Sampling Plans for the Inspection of Isolated Lots of Meters in Service

S-02—Implementation Schedule for the Application of Statistical Sampling Requirements in S-S-01, S-S-02, S-S-03, S-S-04 and S-S-06


Category: Statistical methods
Specification: S-S-06
Document(s): S-S-06 Implementation, Information Bulletin (2010-02-08)
Issue Date: 2010-06-21
Effective Date: 2011-01-01
Supersedes: PS-S-04, LMB-EG-04


Table of Contents


1.0 Scope

This specification establishes the requirements that are applicable to in-service isolated lots of homogeneous electricity or gas meters, where a meter owner has chosen to utilize sampling inspection for the purposes of extending the reverification period of an in-service lot of meters. Where applicable, this specification may be utilized as an alternative to performing 100% meter reverification, upon expiry of a meter lot's initial or subsequent reverification period.

Note: Sampling plans, by design, contain inherent risks and limitations with regard to their usage and the conclusions they may or may not provide. Meter owners are therefore advised that, although conformity with the requirements of this specification may allow for the extension of a meter's reverification period, relying solely on the use of the sampling plans contained in this specification will not provide users with an assurance of compliance with the metering accuracy obligations prescribed under the Electricity and Gas Inspection Act.

2.0 Authority

This specification is issued under the authority of section 19 of the Electricity and Gas Inspection Regulations.

3.0 Normative References

3.1 ISO 2859-2:1985, Sampling procedures for inspection by attributes—Part 2: Sampling plans indexed by limiting quality (LQ) for isolated lot inspection. Table A—Single sampling plans indexed by limiting quality (LQ) (Procedure A).

3.2 S-S-01, Specifications for Random Sampling and Randomization

3.3 Relevant Measurement Canada specification for the verification and reverification of the meter under test.

4.0 Administrative Requirements

Sampling inspection shall be carried out well in advance of the expiry of the reverification period of the meters so that in the case of non-conformity with the requirements, all meters forming part of the lot can be removed from service prior to the expiry of the reverification period.

5.0 Sampling Inspection Requirements

5.1 Lot Formation

5.1.1 The lot shall be formed from meters that are homogeneous with respect to the requirements in Annex A.

5.1.2 At the discretion of a meter owner, larger lots may be reformed into multiple lots of smaller size.

5.2 Sample Selection

5.2.1 The sample shall be drawn at random, without replacement, from the lot listing, using authorized random sampling software that meets the requirements referenced in section 3.2. (Systematic sampling shall not be used).

5.2.2 The size of the sample shall be one obtained from the table in Annex C as per the sampling instructions provided by this specification. The sample representing the lot shall correspond to a value between nmin and nmax as identified in the table of Annex B.

5.2.3 Meter owners shall be responsible for assuring that the meters which are included in the sample meet the following criteria:

  1. the identified meter is one which is currently installed in service;
  2. the identified meter's metrological parameters have not been adjusted post installation;
  3. the identified meter is homogeneous with regard to the criteria of A.1 of Annex A: and
  4. the identified meter meets the total time on test criteria of A.2 of Annex A.

5.2.4 Where a sample meter does not qualify for inclusion as per the requirements of 5.2.3, meter owners shall not consider this meter as part of the sample group for performance testing purposes, and shall replace it with the sequentially subsequent meter on the preselected unsorted sample meter listing meeting the applicable criteria. The exclusion rationale for the subject meter(s) shall be reported as per the requirements of 5.3.4.

5.2.5 Where a meter, which has been removed from service, is not capable of having its performance assessed in accordance with the requirements of this document, the meter owner shall replace it with the sequentially subsequent meter on the preselected unsorted sample listing of meters available for testing. All meters and their associated test results shall be included unless compelling evidence for exclusion is identified and reported as per the requirements of 5.3.4.

5.2.6 Meters which have been excluded as sample meters as a result of not satisfying either 5.2.3 (a), 5.2.3 (b), 5.2.3 (c), 5.2.3 (d) or 5.2.5 shall not be returned to the parent lot.

5.2.7 Lots failing to meet the minimum sample size (nmin) criterion as a result of the total number of exclusions under 5.2.3, are not considered to be homogeneous and are not acceptable for seal extension. Where a lot is deemed to be nonhomogeneous, meter owners shall implement one of the following actions:

  1. Re-form the lot on the basis of both the lot and sample homogeneity criteria contained in Annex A;
  2. Assign a lower initial reverification period to the lot as per the requirements of section 5.7; or
  3. Remove the lot from service.

5.3 Meter Sampling Records

5.3.1 For each lot assessed, a meter owner shall maintain records documenting:

  1. a unique, owner-assigned lot number or record reference which includes an ordinal number indicating the lot's occurrence for assessment under this specification (including the current—i.e. 1st, 2nd, 3rd, etc.);
  2. the homogeneity criteria details specified in A.1;
  3. the utility number and manufacturer's serial number for each meter.

5.3.2 All meters identified by the owner as forming part of the lot, shall be listed in ascending order based on meter identification numbers or an inventory number generated by the associated informatics system.

5.3.3 The identification of each unsorted sample meter (n to nmax) selected from the lot, the sample meters tested, the quality characteristics examined, and the test results obtained, shall be documented.

5.3.4 All sample meters selected but not involved in the final calculations shall be accounted for by the meter owner and the reasons for exclusion shall be documented and, on request, made available for Measurement Canada review. Evidence of deliberate exclusion or improper accounting may disqualify the results of the sample's analysis.

5.4 Meter Inspection, Quality Characteristics, and Corrective Actions

5.4.1 Each sample meter shall be examined for conformance to all pertinent requirements as prescribed by reference 3.3.

5.4.2 Sample meters shall be inspected under identical conditions and within as short a time period as is practicable to achieve valid inspection results.

5.4.3 Each defective meter excluded from the final calculations shall be preserved for Measurement Canada review and shall be the subject of an investigation by the meter owner to determine the cause of the defect or defects. In the case of defective meters, a report shall be prepared and shall include the following information associated with this investigation:

  1. details of the meter's make, model, Notice of Approval number, seal year, and identification numbers;
  2. a description of the defect and its effect on the meter's operation, including performance test results where feasible;
  3. a description of the steps taken to investigate the cause of the defect, including identification of the personnel both performing the investigation and providing information for its purpose;
  4. an explanation of how the defect occurred, including where it occurred in the process;
  5. an evaluation of the extent of the defect in the immediate situation as well as in situations likely to be similarly affected; and
  6. details of the corrective and preventive action proposed or performed to address the cause and symptoms of the defect.

5.4.4 In cases where a defective meter is encountered, the report required by clause 5.4.3 shall be provided to the local Measurement Canada representative for review prior to deciding upon the acceptability of the affected lot. Decisions regarding acceptability of the affected lot and the possible need for further investigation or corrective action shall not be made until Measurement Canada has evaluated the report and the statistical analysis of the data from the sample meters involved in the final calculations.

5.5 Acceptance Criteria

5.5.1 Individual Meters

5.5.1.1 Each meter in the sample can be considered acceptable if the following conditions are met:

  1. the meter complies with all specified reverification performance requirements (reference 3.3);
  2. the meter does not possess any defect which could affect its ability to meet specified requirements during its usage;
  3. the meter has been obtained from a population whose seal year is still valid;
  4. the meter has been received with a broken seal and an exclusion as per 5.3.4 cannot be justified.

5.5.1.2 To maintain overall homogeneity of the lot, sample meters, obtained from lots qualifying for an extension, which meet reverification requirements and which have been granted the same extension as the parent lot, shall, wherever possible, be returned to the parent lot and reinstalled following acceptance of the lot. Alternatively, these meters can be reverified.

5.5.1.3 Where sample meters require their seals to be broken in order to conduct meter performance testing, precautions should be taken to ensure the integrity of the results. If the lot is acceptable, the individual sample meters that are also acceptable shall be resealed with an additional identifier indicating the original seal year in the sealing assembly. Alternatively, these meters shall be reverified.

5.5.1.4 Sample meters that meet reverification requirements, yet have been obtained from lots not qualifying for an extension or sample meters not returned to the parent lot, shall be governed by Measurement Canada bulletins E-26 Reverification Periods for Electricity Meters and Metering Installations or G-18 Reverification Periods for Gas Meters, Ancillary Devices and Metering Installations, with respect to the assigned reverification period.

5.5.2 Meter Lots

5.5.2.1 The sampling plan parameters of ISO 2859-2 (reference 3.1) as modified in Annex C of this document, shall be utilized for the inspection of isolated lots of meters in service.

5.5.2.2 The acceptability of the lot for the purposes of extending its reverification period, shall be established on the basis of the performance results of the sample with regard to the number of marginally conforming meters (C1) and the number of nonconforming meters (C2) evidenced, as defined in section 5.5.3.

5.5.2.3 Contractors are responsible for ensuring the performance quality of the in-service meter lots which they own. Where a seal extension period is available under this specification, contractors shall give consideration to their statutory obligation for keeping meters in good repair, when selecting the seal extension period to be applied from those which are available. Specifically, the conformance quality of an in-service lot of meters shall, in all cases, meet or exceed the declared limiting quality that is associated with level 5.

5.5.3 Meter Performance Test Limits

5.5.3.1 For all performance tests, required to be conducted as per the reverification specification applicable to the subject meter type or class, a Type 1 (C1) marginally conforming meter is one whose performance error exceeds ± 2.0% at any test point.

5.5.3.2 For all performance tests, required to be conducted as per the reverification specification applicable to the subject meter type or class, a Type 2 (C2) nonconforming meter is one whose performance error exceeds ± 2.9% at any test point.

5.5.3.3 For the purposes of section 5.5.2.2, a Type 2 (C2) nonconforming meter is also counted as a Type 1 (C1) marginally conforming meter.

5.5.4 Seal Extension Levels

5.5.4.1 Where a lot of meters is assessed against the requirements of this specification, the maximum seal extension level available for application to the lot, shall be established on the basis of satisfying the following criteria when applied to the nmin sample size as specified in a column of the applicable Annex C table:

Maximum Extension Level Criteria:

  1. c1 ≤ Ac type 1
  2. c2 ≤ Ac type 2

5.5.4.2 Subject to the requirements of section 5.6, the maximum seal extension level that may be available for application to a lot, is the seal extension level associated with the limiting quality column of the applicable table in Annex C, C-1 or C-2 which satisfies the requirements of 5.5.4.1 for the established sample size nmin.

5.5.4.3 Where the maximum level of extension available to a lot of meters is determined to be level 4, the applicable seal extension period, as determined under Annex E, may be repeated without limitation on an ongoing basis where the applicable level 4 limiting quality criteria of Annex C, C-1 or C-2 and the Time on Test criteria of Annex E are met.

5.5.4.4 Subject to section 5.5.4.5, lots failing to meet at least level 4 criteria are not acceptable for extension. All meters in non-acceptable lots shall be removed from service.

5.5.4.5 Where a lot failing to meet level 4 criteria is capable of meeting the limiting quality criteria of level 5 (where available), the applicable level 4 extension period available as per Annex E, may be applied to the lot. However, upon expiry of this period, the lot cannot be re-sampled and must be removed from service.

5.5.4.6 Where a lot fails to meet at least level 4 criteria and this failure is as a result of not meeting the requirements of sec 5.5.4.1(ii), all sample meters identified as C2 meters under section 5.5.3.2 shall be held in storage until Measurement Canada authorizes their further processing. Sample meters shall not be required to be held in storage (without just cause) after December 31st of the calendar year in which the sampling was conducted.

5.6 Use of Sampling Tables (Annex C, C-1, and C-2)

5.6.1 The value of nmin shall be established on the basis of the lot size and the maximum seal extension level being targeted. Once the nmin sample size has been determined, it is this value that shall be utilized for establishing the maximum seal extension level, where further movement within the table is limited to either the horizontal or a diagonal downward direction for the same nmin.

5.6.2 Notwithstanding the seal extension level available under the requirements of section 5.5.4.1, and subject to section 5.6.3, the maximum seal extension level that may be applied to the lot shall be established on the basis of the lot's ordinal sampling occurrence under this specification as specified in Annex D.

5.6.3 Where the maximum seal extension level available to the lot under Annex D is longer in duration than the previous seal extension period granted to the lot, the period applied shall not be greater than one level better than the previous extension level and this eligibility for the application of a longer period, is limited to a single occurrence within a meter lot's in-service life.

5.6.4 Where a lot population has never been assessed against the requirements of this specification, the seal extension period of reference for the purposes of 5.6.3, shall be the last extension period granted to the lot under the previously authorized compliance sampling program.

5.6.5 Where a lot population is re-formed under the requirements of 5.1.2 or 5.2.7, the maximum seal extension levels available to the re-formed lot shall be established in accordance with the requirements of 5.6.2, 5.6.3, and 5.6.4, as applicable to the parent lot before re-formation.

5.6.6 Where a lot's population size is 500 meters or less, a meter owner may, at their discretion, utilize the sampling plan as specified in Annex C-1. Where the sampling plan of Annex C-1 is utilized, the seal extension periods available under Annex E are reduced by 50% (rounded down to the nearest whole year).

5.6.7 Where a lot's population size is 60 meters or less, a meter owner may, at their discretion, utilize the sampling plan as specified in Annex C-2. Where the sampling plan of Annex C-2 is utilized, the only seal extension periods available under Annex E are those associated with a level 4 extension.

5.7 Seal Extension Periods (Annex E)

5.7.1 For meter lots still within their initial reverification period, the time on test (TT) requirements which need to be met or surpassed by each meter in the sample (as per the homogeneity requirements of A.2), shall be established on the basis of the meter's initial reverification period and the minimum period (in months) prescribed under Annex E.

5.7.2 For meter lots still within their initial reverification period, a sample meter's time on test (in months) is established from the date the sample meter is placed into service, to the date that it is removed from service (rounded down to the nearest whole month). For the purposes of this section and section 5.7.4, where months are established on the basis of day counts, one month is to be considered 31 days. Alternatively, months may be established on the basis of actual month days where this information is tracked on an ongoing basis relative to true months completed within a calendar period.

5.7.3 Subject to section 5.7.5, where a meter lot is no longer within its initial reverification period, the time on test (TT) requirements that need to be met or surpassed by each meter in the sample (as per the homogeneity requirements of A.2), shall be established on the basis of the previous seal extension period granted to the lot and the applicable subsequent extension percentage prescribed for the subject row as per Annex E.

5.7.4 For meter lots no longer within their initial reverification period, a sample meter's time on test (in months) is established from the date that the certificate was issued relative to the meter lot's last seal extension, to the date that the sample meter is removed from service (rounded down to the nearest whole month). Alternatively, a meter's time on test requirement is satisfied where it can be demonstrated that the sample meter has continuous uninterrupted service.

5.7.5 Meter lots that are sampled on an annual basis under this plan, are not subject to the time on test requirements of Annex E.

5.7.6 Where the time on test requirements for the 1st extension or subsequent extensions of a lot have not been met or where a sample is deemed non-homogeneous relative to the applicable time on test requirement, a lower initial reverification period (where the time on test requirements are satisfied) may be assigned to the lot.

5.7.7 Once a lower initial reverification period row has been assigned to a lot, further movement within the table is limited to either the horizontal, downward or diagonal downward directions (i.e. the initial reverification period reference cannot be increased on subsequent samplings of the lot).

5.8 Reverification Date Calculations

5.8.1 Subject to 5.8.2 , where a seal period extension is granted under Annex E, the meters in the lot, less any nonconforming meters, shall be considered due for reverification on or before December 31 of the calendar year calculated as the sum of the year in which the first sample meter was removed from service and the extension period granted under Annex E (in years).

5.8.2 Where the first sample meter is removed from service in the calendar year which immediately precedes the meter lot's seal expiration year, the meters in the lot, less any nonconforming meters, shall be considered due for reverification on or before December 31 of the calendar year calculated as the sum of the lot's seal expiration year and the extension period granted under Annex E (in years).

5.8.3 Subject to 5.8.4, where a lot of meters fails to meet the requirements for an extension of its reverification period, the meters in the lot shall be considered due for reverification on the date established by the previous verification or reverification, as the case may be.

5.8.4 In the case of a lot of meters which fails to meet the requirements for an extension of its reverification period and the first sample meter was removed from service in a calendar year which preceded the meter lot's seal expiration year by more than one (1) calendar year, the meters in the lot shall be considered due for 100% reverification, on or before December 31st of the calendar year which postdates the year in which the first sample meter was removed from service.

Annex A

(normative)

A.1 Lot Homogeneity Requirements

Where applicable, the meters in the lot shall be homogeneous with respect to the following characteristics:

Electricity Meters

  1. type (transformer or self contained);
  2. manufacturer and model, unless otherwise authorized in accordance with clause A.1.1;
  3. voltage or voltage range;
  4. maximum current range, unless otherwise authorized in accordance with clause A.1.1;
  5. measurement functions (e.g. measured quantities, energy, demand), unless otherwise authorized in accordance with clause A.1.1;
  6. firmware version, unless otherwise authorized in accordance with clause A.1.1;
  7. frequency rating;
  8. same model or type of telemetering device (if so equipped), unless otherwise authorized in accordance with clause A.1.1;
  9. configuration / form (i.e. number of elements Footnote 1, wye, delta or auto configuration);
  10. status at time of last inspection (i.e. new, renewed, or reserviced);and
  11. seal year (same seal year or two consecutive seal years, provided both are valid);

Natural Gas Meters

  1. manufacturer and model, unless otherwise authorized in accordance with clause A.1.1.
  2. same or similar capacity rating, unless otherwise authorized in accordance with clause A.1.1.
  3. measurement functions (e.g. measured quantities, temperature/pressure conversion).
  4. firmware version, unless otherwise authorized in accordance with clause A.1.1.
  5. same model or type of telemetering device or auxiliary attachment (if so equipped), unless otherwise authorized in accordance with clause A.1.1.
  6. status at time of last inspection (i.e. new, renewed, or reserviced).
  7. seal year (same seal year or two consecutive seal years, provided both are valid).

A.1.1 Forming Lots with Mixed Meters

Where a lot includes meters which, for the purposes of lot homogeneity, are ones which possess a similar characteristic rather than a characteristic which can be readily identified as being the same, meter owners are responsible for maintaining documented records identifying the similarities which support the homogeneity conclusion (as concerns including these meters within the subject lot). For the purposes of compliance sampling, if an accredited organization wishes to combine, in one lot, various models or vintages of meters, and/or meters equipped with and without a telemetering device, the accredited organization shall submit a request to MC with accompanying documentation in support of their claim that these differing meters can be considered homogeneous.

A.2 Sample Homogeneity Requirements

The meters in a sample shall be homogeneous with respect to similar time in usage. For a sample meter to be considered homogeneous with regard to similar time in use, a meter shall have been in service for a time period that meets or exceeds the applicable time on test (TT) requirements of Annex E. Where nmin is not achieved with regard to this criteria, a meter owner may re-form the lot or reduce the seal period extensions available as per the requirements of section 5.7.

Annex B

(normative)

Table 1—n min to n max Sample Sizes
n min n max
30 37
42 52
44 55
65 81
80 100
125 156
200 250
315 394

Annex C

(normative)

Table 2—Single Sampling Plans Indexed by Limiting Quality (LQ)
Lot Size Limiting Quality (LQ)
3.15
(Level 1)
5.0
(Level 2)
8.0
(Level 3)
12.5
(Level 4)
20.0
(Level 5)
nmin, Ac type 1, Ac type 2
Up to 500 80, 0, 0 65, 0, 0 not
available Footnote 2
not
available Footnote 2
not
available Footnote 2
501 to 1200 125, 1, 1 80, 1, 0 65, 1, 0 42, 2, 0 42, 4, 0
1201 to 3200 125, 1, 1 125, 3, 1 80, 3, 0 65, 4, 0 65, 8, 0
3201 to 10000 200, 3, 3 200, 5, 3 125, 5, 1 80, 5, 1 80, 10, 1
10001 to 35 000 315, 5, 5 315, 10, 5 200, 10, 3 125, 10, 3 125, 18, 3
over 35000 not available not available 315, 18, 5 200, 18, 5 200, 32, 5

Note:

Maximum permissible lot size is 35000

As per 5.5.3.1, Type 1 (C1) > 2.0%

As per 5.5.3.2, Type 2 (C2) > 2.9%

Footnotes

Footnote 2

move down targeted Level column to criteria for Lot Size of 501 to 1200

Return to footnote 2 referrer

Annex C1

(normative)

Table 3—Small Lot Size Plan (with increased sampling frequency)
Lot Size Limiting Quality (LQ)
5.0
(Level 1) Footnote 3
8.0
(Level 2) Footnote 3
12.5
(Level 3) Footnote 3
20
(Level 4) Footnote 3
nmin, Ac type 1, Ac type 2
Up to 500 44, 0, 0 44, 1, 0 44, 2, 0 44, 4, 0

Note:

As per 5.5.3.1, Type 1 (C1) > 2.0%

As per 5.5.3.2, Type 2 (C2) > 2.9%

Footnotes

Footnote 3

Extension period as per section 5.6.6.

Return to footnote 3 referrer

Annex C2

(normative)

Table 4—Very Small Lot Size Plan
Lot Size Limiting Quality (LQ)
(Nonconforming)
5.0
(Level 4)
nmin, Ac type 1, Ac type 2
Up to 60 30, 0, 0

Note:

As per 5.5.3.1, Type 1 (C1) > 2.0%

As per 5.5.3.2, Type 2 (C2) > 2.9%

Annex D

(normative)

Table 5—Maximum Seal Period Extension Levels Available
Ordinal Sampling Occurrence Maximum Seal Period Extension Level
1st Level 1
2nd Level 2
3rd Level 3
4th
(and higher)
Level 4

Annex E

(normative)

Table 6—Time on Test (TT) Requirements and Maximum Seal Period Extensions
Initial Reverification Period (years) 1st Extension (Months) Subsequent Extensions Footnote 4 Maximum Seal Period Extension (years)
Level 1 Level 2 Level 3 Level 4
12 115 75% 10 8 5 2
11 105 75% 9 7 5 2
10 84 70% 8 6 4 2
9 75 70% 7 5 3 2
8 67 70% 6 4 3 2
7 58 70% 5 4 2 1
6 50 70% 4 3 2 1
5 42 70% no Level 1 extension 3 2 1

Footnotes

Footnote 4

Subsequent extension TT based on indicated percentage multiplied by the previous extension (rounded up to the next whole month).

Return to footnote 4 referrer

Footnotes

Footnote 1

With the exception that 1-element and 1.5-element meters may be mixed to form a lot.

Return to footnote 1 referrer

Date modified: