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Engineering Guidelines 
 
 
 
GS-ENG-03-06: Certification of Gas Measuring Apparatuses 
Containing Rotary Meters Used for the Purpose of Calibrating 
Diaphragm Meters 
 
 
 
 
 
 
 
 
Version 1.02 
 
 
 
 
 
 
 
 
 
 
 
 
Patrick (Pat) J. Hardock, P.Eng. 
Senior Engineer – Natural Gas Measurement 
Engineering and Laboratory Services Directorate 
Measurement Canada 
 
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RECORD OF CHANGE 
 
 
Revision Date Description 
0.1 2003-05-07 Gs-Eng-03-Nobell.rev3.wpd 
0.2-0.3 2004-10-20 
Section 8.2 and 9.0 revised to emphasize check 
meter usage 
0.3-0.5 2004-11-02 
Section 9.0 revised to add comments from PDD e-
mail Dated Tue 2004-10-26 11:15 
0.6 2006-09-26 
Added discussion of control charting and 
measurement Uncertainty. 
0.7 2006-09-26 Added editorials 
0.8 2007.01.12 Added section 11.0 
0.9 2007.02.01 
Clarification of use of level 1 & 2 Master Bell 
Provers, alternative check meters and expanded 
scope to include additional diaphragm meters. 
Version 1.0 2007.02.02 Editorials 
Version 1.01 2007.02.05 Editorials 
Version 1.02 2007.02.27 Editorials 
 
 
 
 
 
 
 
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1.0 Scope 
 
The purpose of this Instruction is to clarify the process of certification of gas measuring 
apparatuses containing rotary meters used for the purpose of calibrating diaphragm meters. This 
document must be read in conjunction with the references listed below. 
 
 
2.0 References 
 
(a) Draft Specifications for the Calibration, Certification and the Use of Gas Measuring Apparatus 
- Low Pressure Meter Provers 
 
(b) S-G-01, Specifications for the Calibration, Certification and Use of Gas Measuring Apparatus - 
Working Level Sonic Nozzle Provers 
 
(c) GL-CP-002: Calibration Procedure for the Certification of Reference Meters Used in Low 
Pressure Transfer Provers Document Number, Version: 01 
 
(d) GS-ENG-06-01, Recommendations for the Determination of Measurement Uncertainty, In Two 
Meter Comparisons, 
 
(e) Engineering Instructions for the Determination of Measurement Uncertainty for Two Meter 
Comparisons Using Numerical Analysis Software, GS-ENG-06-02 
 
(f) Measurement Uncertainty and Meter Conformity Evaluation Specification, 
 Measurement Canada, S-S-02, 2007 
 
 
3.0 Introduction and Background 
 
Measurement Canada certification procedures for gas measuring apparatus can generally be 
divided into two basic types or categories. The first is based on a set of methods and 
philosophies presented in the current bell prover and sonic nozzle prover specifications. The 
second is based on common practices and experience with rotary meter transfer provers and large 
test facilities. 
 
In the case of rotary meter provers used for the purpose of verifying diaphragm meters, an 
examination of the two methods reveals that there is no great compelling technical reason to 
choose one method over the next. This is not to suggest that neither method would need to be 
adapted to fit rotary meter based diaphragm meter provers. The purpose then of the remainder of 
the document is to help establish the differences between the present bell prover and sonic nozzle 
prover specifications and those which need to be considered as a result of the differing technology 
base. This document recognizes the traditional method of on-going measuring apparatus 
correlation with a master bell prover but, allows for reduced bell prover corrections provided that 
continual system monitoring is conducted using a stable check meter. 
 
Specifications specifically addressing rotary meter based measuring apparatus have not yet been 
developed and promulgated. However, Measurement Canada specifications covering all types of 
low-pressure transfer provers are currently in the process of being developed jointly with the gas 
meter industry, as part of the Natural Gas Trade Sector Review (NGTSR) implementation process. 
The typical time required to complete a new specification, when performed by or administered by 
a national standards writing body, is in the order of two years. As such, the following document is 
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intended to provide interim guidance to manufacturers, owners and operators of rotary meter 
based provers until these new specifications have been completed. 
 
Until such time as the new specification is promulgated, selective sections of the draft 
Specifications for the Calibration, Certification and the Use of Gas Measuring Apparatus Low 
Pressure Meter Provers, Specifications for the Calibration, Certification and Use of Gas 
Measuring Apparatus - Working Level Sonic Nozzle Provers and the Evaluation Guidelines for 
Reference Meter Test Data Used for the Certification of Measuring Apparatuses, GS-Eng-02-10 
will be used by Measurement Canada Engineering and Laboratory Services Directorate (ELSD) to 
certify rotary meter based provers. 
 
 
4.0 Process Overview 
 
When a measuring apparatus is of a design or type that is not governed by a promulgated 
specification and the owner or operator wishes to use this apparatus for the purpose of verification, 
reverification or compliance sampling authorized under the authority of the Electricity and Gas 
Inspection Act, the following process will be applied. 
 
4.1 Making Application to Measurement Canada 
 
The administrative processes described in section 4.0 of S-G-01, Specifications for the 
Calibration, Certification and Use of Gas Measuring Apparatus - Working Level Sonic Nozzle 
Provers, are directly applicable with the following additional requirements. 
 
Piping and instrumentation drawings, component specifications and user manuals should be 
provided by the applicant for review. Block diagrams as well as explanations of controlling 
software should also be included. This information should be sent to and/or gathered by the 
Measurement Canada Regional Gas Specialist. Once he/she is satisfied that the information is 
complete, it should be forwarded to Measurement Canada Gas Engineering for review. Once this 
package of information has been reviewed and any modifications to the intended test plan 
determined, initial testing can commence. 
 
As this time it is also recommended that the manufacturer provide a reference meter calibration 
test plan for pre-approval to ELSD. The calibration test plan should be consistent with reference 
to the Evaluation Guidelines for Reference Meter Test Data Used for the Certification of 
Measuring Apparatuses GS-Eng-02-10. The purpose of this pre-review is to avoid any 
unnecessary duplication in testing or calibration. 
 
4.2 Initial Testing and Review 
 
Once the reference meter has been calibrated and a certificate of calibration issued by ELSD, on-
site evaluation can commence. 
 
The on-site certification will be performed in accordance with the principles contained in references 
(a) and (b). Once compliance with these requirements is demonstrated, the test data and reports 
will be sent by the Regional Gas Specialist to ELSD for review. Upon revi ew and acceptance, a 
certificate for the measuring apparatus may then be issued by this authority. 
 
4.3 Certification Periods 
 
For the purpose of certification of a measuring apparatus for which specifications have not been 
promulgated, a one-year certification period based on these interim guidelines will be applicable. 
 
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When the reference meter(s) contained in the apparatuses has been calibrated using methods 
and laboratories acceptable to Measurement Canada, the meter(s) will receive a separate 
certification from ELSD for a period of five years. 
 
 
5.0 Certification of Prover’s Reference Meter 
 
When Measurement Canada is unable to perform the required calibration testing, laboratories 
recognized by Measurement Canada in bulletin G-16(rev.3) shall be used instead. The 
permissible uncertainty, required number and distribution of test points and manner of handling 
data, is all described in the Evaluation Guidelines for Reference Meter Test Data Used for the 
Certification of Measuring Apparatuses (GS-Eng-02-10.rev.2), and is applicable to this type of 
measuring apparatus. 
 
In general, the following requirements shall apply: 
 
(a) The calibration of the reference meter should be established at a Measurement Canada 
recognized test facility or using a certified proving apparatus. 
 
(b) The calibration of the meter should be established over the intended range of its operation at a 
sufficient number (usually 15) of test flow rates. 
 
(c) The test flow rates should be distributed based on the meter’s characteristic operating curve 
and the intended range of use. 
 
6.0 Use of Measurement Canada Supplied Data in Flow Computers Associated 
with Measuring Apparatus 
 
In order to use the data provided on Measurement Canada’ s certificate of calibration for the 
reference meter, to its fullest potential, various linearization schemes will need to be employed in 
the flow computer/instrumentation associated with the reference meter. Where such schemes are 
not employed, the measuring apparatus will be restricted to use in the linear portion of the 
reference meter’s performance curve. 
 
Where point-to-point linearization schemes are used, the values may be taken directly from the 
certificate provided by Measurement Canada. If additional values are needed they can be 
calculated from the supplied coefficients. 
 
 
7.0 Security of Prover Calibration Data 
 
In order to ensure that the integrity of the measuring apparatus is maintained throughout its 
certification period, the following information shall be provided to ELSD and will constitute part of 
the certificate issued for the measuring apparatus: 
 
(a) All pressure, temperature, reference meter and calibration factors 
(b) Any additional preset values determined during the initial verification of the apparatus 
 
Records should be kept at the site such that: 
 
(a) This data will be accessible for audit purposes 
(b) Any changes to calibration data will be readily detectable under audit 
 
 
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8.0 Determination of Measurement Uncertainty 
 
Prior to the initial certification process, the system measurement uncertainty, reported at the 95% 
confidence interval, should be determined by the contractor. Guidance on this determination can 
be found in references (d) and (e). The measurement uncertainty should be determined for each 
class or type of transfer meter in a manor that represents the intended use of the measuring 
apparatus. A statistical estimate for the MUTs repeatability should also be included. Assistance 
can be provided by Measurement Canada Engineering in the application of the papers. A detailed 
copy of the completed analysis should be sent to Measurement Canada Gas Engineering for 
review. 
 
8.1 Establishment of Traceability 
 
Regardless of the method chosen for the certification of the measuring apparatus, traceability is 
maintained by periodic comparison to the local level 2 master bell prover. The frequency of this 
comparison is dependent on section 10.0. Under specific circumstances, traceability can be 
established directly to level 1 standards held by Engineering and Laboratory services in Ottawa. 
 
 
9.0 Initial On-site Evaluations of Measuring Apparatuses 
 
The initial evaluation of the gas measuring apparatus shall be performed at a location mutually 
acceptable to all parties involved, and must be consistent with the above references such that the 
following tests listed in Table 1 can be performed. 
 
Table 1: Initial On-site Evaluations of Measuring Apparatuses 
 
# Test Name Reference Specification or Requirement 
1 Environmental controls Section 5.1 of S-G-01. 
2 Operational leak test Section 5.3.1 of S-G-01. 
3 Flow rate tests Section 5.3.2 of S-G-01. 
4 Register verification Section 5.3.3 of S-G-01. 
5 Maximum error detection Section 5.5.4 of S-G-01. 
6 Modified correlation and preset 
value determination 
See 8.2 below for details 
7 Pressure sensors Accuracy of registered reading at sufficient 
number of points over intended range of 
operation (tol. = +/- 0.2 in. w.c.) 
8 Temperature sensors Accuracy of registered reading at sufficient 
number of points over the controlled 
temperature range of the test environment 
(tol. = +/- 0.5°F) 
9 Programming of prover controller Verification of pressure and temperature 
corrections using registered values (no error 
permitted) 
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Verification that the reference meter’s 
certified calibration curve results were 
entered correctly into the prover software. 
 
 
9.1 Selection and use of Transfer Meters for Initial Evaluation 
 
The Draft Specifications for the Calibration, Certification and the Use of Gas Measuring Apparatus 
- Low Pressure Meter Provers discusses the concepts of transfer meters and check meters. 
These concepts will be applied here. Specifically, for measuring apparatus specifically intended to 
verify diaphragm meters, transfer meters should be selected for each make and model of 
diaphragm meter included in the statement of intended use. The concept of classes of transfer 
meters will not be applied; however the requirements for the performance of diaphragm transfer 
meters should be consistent with those in section 5.4.2 of S-G-01. 
 
9.2 Modified Volume Correlations and Determination of Prover Preset Values 
 
Present specifications for the use of bell and sonic nozzle provers provide for the use of preset 
calibration values to eliminate any perceived bias between the local master bell prover and the 
measuring apparatus. 
 
These presets can be applied to classes of diaphragm meters or alternatively to each type or 
model of meter shown on the Statement of Intended Use. In order to determine which option is 
acceptable, it is recommended that each type/model of meter be used and the results analyzed, 
to determine if the concept of meter classes can be applied. The testing associated with this 
process would be consistent with the correlation process described in section 5.5.3 of S-G-01. 
 
Alternatively, provided that at the time of certification, the differences between the values of the 
transfer meter’s performance found using the master bell prover and the rotary meter prover are 
within the expected bounds of the individual measuring apparatuses’ uncertainty, then the 
difference between the two values can be considered as not significant and no preset corrections 
need to be applied. 
 
This value should not exceed the root sum squared of the uncertainty (k=2) of the measuring 
apparatus (±0.3%), the master bell prover (±0.2%) and an allowance for the variation in the transfer 
meter (±0.3%). Therefore a value of {(±0.3%)2 + (±0.2%)2 + (±0.3%)2}1/2 = ±0.5% should be 
considered as a estimate of the maximum permissible value. Please not that this estimate allows 
for both bias and random errors. 
 
It is also recommended that the determination of presets be performed by the owner of the 
apparatus based on their documented procedures, and the application or programmingof presets 
be completed prior to the initial evaluation testing of the apparatus. This testing would be 
effectively repeated by the Measurement Canada representative during the initial evaluation of the 
measuring apparatus. 
 
At the time of initial evaluation of the measuring apparatus, the tests described in section 8.0 
should be performed, based on the procedures in S-G-01. 
 
9.3 Use of Prover Preset Values 
 
If chosen, the preset values determined for the purpose of initial evaluation of the measuring 
apparatus, once programmed, should not be modified until the next certification process. These 
values should be recorded and form a part of the information forwarded to Measurement Canada’s 
Engineering and Laboratory Services for inclusion in the certificate of calibration of the measuring 
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apparatus. 
 
 
10.0 Post-certification Usage Requirements 
 
As discussed in the introduction there are two possible methods for the long term tracking of the 
rotary piston prover’s performance. 
 
In the first case those applicants which use rotary meter based provers along with bell provers 
may choose to perform the daily and weekly correlation process similar to that specified for 
working level bell provers. This method is deemed acceptable, provided there are no changes in 
the system’s presets values. The frequency of the comparison can be reassessed once a 
statistically significant number of comparisons have been completed. This information can then be 
used to determine the long-term standard deviation for each particular class of MUT and establish 
monitoring/correlating frequencies. 
 
Again, in the second case the concept of check metering is utilized. Check meters should be 
selected based on the meter classes established in S-G-01. The method of tracking the 
measuring apparatus’s performance should be based on established statistical process control 
procedures. The documented method and handling of the data should form part of the information 
presented to Measurement Canada with the initial documentation. The written SPC procedure 
should be submitted to MC's Senior Gas Engineer detailing the SPC method, control limits and 
how it is to be updated. A sample spreadsheet for this purpose is available from Measurement 
Canada Gas Engineering. Again, the contractor is to ensure that his choice of "control meters" 
adequately represents all of the classes of meters to be tested on the prover. 
 
Where check meters of a differing principle of operation from those of the meters under test is 
selected (alternative check metering), a period of inter-comparison between the alternative check 
meter, the check meter selected based on the meter classes established in S-G-01 and the 
level 1 master bell prover shall be established. Where sufficient data has be collected and 
presented at the time of recertification to demonstrate that the alternative check meter provides 
the same level of confidence as those based on the meter classes in S-G-01, the use of the 
check meters based on the class system may be suspended. Again, the frequency of the 
comparison can be reassessed once a statistically significant number of comparisons have been 
completed. 
 
Where the stability of the check meter or alternative check meter has been demonstrated by 
comparison to the local level 2 master bell prover or other means authorized by Measurement 
Canada Engineering, traceability can be established directly to level 1 standards held by 
Engineering and Laboratory services in Ottawa. 
 
These procedures should also address the stability of the temperature and pressure measuring 
devices contained in the apparatus. 
 
 
11.0 Re-certification Requirements 
 
The certificate of calibration for each measuring apparatus is valid for a period of one year. The 
annual re-evaluation of the gas measuring apparatus shall be performed at a location mutually 
acceptable to all parties involved, and must be consistent with the above references such that the 
following tests listed in Table 2 can be performed. 
 
 
 
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Table 2: On-site Re-evaluations of Measuring Apparatuses 
 
# Test Name Reference Specification or Requirement 
1 Environmental controls Section 5.1 of S-G-01. 
2 Operational leak test Section 5.3.1 of S-G-01. 
6 Modified correlation and preset 
value determination 
See 8.2 above for details 
7 Pressure sensors Accuracy of registered reading at sufficient 
number of points over intended range of 
operation (tol. = +/- 0.2 in. w.c.) 
8 Temperature sensors Accuracy of registered reading at sufficient 
number of points over the controlled 
temperature range of the test environment (tol. 
= +/- 0.5°F) 
Verification of pressure and temperature 
corrections using registered values (no error 
permitted) 
9 Programming of prover controller 
Verification that the reference meter’s certified 
calibration curve results were entered correctly 
into the prover’s software. 
 
 
The control charts shall also be reviewed to ascertain if the system is in control and that the 
measurement uncertainty determined at the time of initial calibration is still valid. If it is not it shall 
be modified accordingly. 
 
Where alternative check metering is used, a summary of the inter-comparison between the 
alternative check meter, the check meter selected based on the meter classes, and the level 2 
master bell prover shall be presented.