Nov. 04, 2024
Calibration of gas meters has become a necessity nowadays. Several methods are applied for performing gas meters&#; calibration. The most common ones are:
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Bell
Prover:
This is actually a calibrated vessel with well-known volume characteristics. It is often used as a primary standard. The Bell Prover provides a certain volume to the gas meter under test and thus a direct comparison between the meter&#;s reading and the volume&#;s value can be performed. This method is mainly used for calibrating small domestic / diaphragm meters.Gravimetric method
: A very accurate weighing scale is used to define the amount of gas that actually flows through the meter during the calibration procedure. This method is considered to be very accurate.Test Bench:
It is a complete system which uses master meters as reference standards. The same amount of volume flows through the master meter and the gas meter under test, and the two meter readings are compared to each other. This method is widely used by many calibration laboratories all over the world. Depending on the size of the master meters, high flowrates can be achieved and very large gas meters can be calibrated.Before proceeding with the analysis of the Test Bench method of calibration, it is important to give some information about the metrological characteristics of the most common types of gas meters.
When a gas meter is calibrated, the result reported in the calibration report is the % Error of Indication which must be measured in specific flow points (depending on the meter&#;s type and rangeability). Error of Indication (f) is defined as follows:
[math]f=\frac{V_{MUT}-V_{TRUE}}{V_{TRUE}}-100 \%[/math]
Where:
VMUT = Volume Reading of the MUT
VTRUE = Actual Volume that flowed through the MUT
Based on these measurements, a calibration curve can be included in the calibration report. A typical calibration curve can be seen below:
The black curve indicates the Error of Indication of the gas meter in several flow points, while the red lines represent the error limits (maximum permissible error) for the specific type of meter. Error limits as well as measurement flow points are specifically defined within the corresponding European Standards for each type of gas meter.
Diaphragm Meters
According to EN the error limits of Diaphragm gas meters are shown in the following table:
Diaphragm Gas meter Error Limits
Flow Rate Q
Limits
Qmin &#; Q < 0,1Qmax
± 3,0 %
0,1Qmax &#; Q &#; Qmax
± 1,5 %
The flow points for the calibration of a diaphragm meter are Qmax, 0,2Qmax, Qmin.
Rotary Displacement meters
For Rotary Displacement meters, the error limits are defined according to EN :
Rotary Displ. Gas meter Error Limits
Flow Rate Q
Limits
Qmin &#; Q < Qt
± 2,0 %
Qt &#; Q &#; Qmax
± 1,0 %
Where Qt (Transitional Flowrate) is given by the following table:
Flowrate Range (Qmin/Qmax)
Qt
&#; 1:20
0,20 · Qmax
1:30
0,15 · Qmax
1:50
0,10 · Qmax
> 1:50
0,05 · Qmax
EN also specifies that the meter must be calibrated at the following flow points depending on the meter&#;s rangeability (Qmin/Qmax):
Test flow rates in % of Qmax
Rangeability
1:10 to 1:30
&#; 1:50
Qmin
Qmin
5
5
10
15
25
25
40
40
70
70
100
100
Turbine meters
Turbine gas meters are calibrated according to EN which specifies the following error limits:
Turbine Gas meter Error Limits
Flow Rate Q
Limits
Qmin &#; Q < Qt
± 2,0 %
Qt &#; Q &#; Qmax
± 1,0 %
Where Qt (Transitional Flowrate) is given by the following table:
Flowrate Range (Qmin/Qmax)
Qt
1:10
0,20 · Qmax
1:20
0,20 · Qmax
1:30
0,15 · Qmax
&#; 1:50
0,10 · Qmax
The test flow rates for turbine gas meters are defined as follows:
Test flow rates in % of Qmax
Rangeability
1:10
1:20
1:30
1:50
2
3
5
5
5
10
10
10
15
25
25
25
25
40
40
40
40
70
70
70
70
100
100
100
100
Calibrating gas meters with the Test Bench method
The Test Bench consists of:
In the above figure the master meters used are one G16 and one G650 covering a total flow range of 0,5m3/h to m3/h. Usually rotary displacement meters with dual impellers are used in order to eliminate pulsation and resonance to the flow profile. In large test benches, where high flow rates must be achieved, turbine meters are also used as master meters.
In the case that the Calibration Medium is air at atmospheric pressure (which is an acceptable method for calibrating gas meters which operate at a pressure lower than 4 bar, as defined in EN ), the principal of operation of the Test Bench is described below.
The air enters through the filters (with the fan operating in suction mode) and flows through the master meter. The flow is adjusted via the control valves and the speed of the fan. The air passes through the meter under test and returns to the room exiting from the fan.
A temperature and a pressure sensor are placed on each meter (master meter and meter under test).
The test bench must have the capability to monitor the pressure drop at the meter under test as well as leakages at any part of the installation.
During the measurement (at each flow point) the following data are measured at the master meter and at the meter under test:
The indication error of the meter under test results from the comparison of the readings of the meter under test and the master meter and is given from the following formula:
[math]f_{MUT}=(\frac{V_{MUT}-(1+f_{STD}/100)P_{MUT}-T_{STD}}{V_{STD}-P_{STD}-T_{MUT}}-1)-100 \%[/math]
For more information, please visit Bell-Prover Gas Meter Test Bench.
Where:
[math]V_{MUT}=\frac {N_{MUT}}{F_{MUT}}[/math][math]V_{MUT}=\frac {N_{MUT}}{F_{MUT}}[/math]
and
[math]V_{MUT}=\frac {N_{MUT}}{F_{MUT}}-\frac{t_{MUT}}{t_{STD}}[/math][math]V_{MUT}=\frac {N_{MUT}}{F_{MUT}}-\frac{t_{MUT}}{t_{STD}}[/math]
Where:
VMUT : The volume of the meter under test
VSTD : The volume of the master meter
fSTD : The error of indication of the master meter (taken from the master meter&#;s calibration report)
PMUT : The pressure measured at the meter under test
PSTD : The pressure measured at the master meter
TMUT : The temperature measured at the meter under test
TSTD : The temperature measured at the master meter
NMUT : The number of pulses of the meter under test during the measurement
NSTD : The number of pulses of the master meter during the measurement
FMUT : The pulse value of the meter under test (written on the meter&#;s index)
FSTD : The pulse value of the master meter (taken from the calibration report)
tMUT : The measurement time of the meter under test
tSTD : The measurement time of the master meter
Specifications regarding the pressure and temperature measurement points, the upstream and downstream piping and the pressure loss measurement are mentioned in the relevant European Standards (EN , EN , etc.).
Useful information regarding construction and operation of Test Benches are also given in PTB Band 29 Guide &#;Testing of volume gas meters with air at atmospheric pressure&#;.
Measurement Uncertainty
When using a Test Bench to calibrate gas meters, similar to the one described above, there are several sources of measurement uncertainties:
Based on the formula mentioned above:
[math]f_{MUT}=(\frac{V_{MUT}-(1+f_{STD}/100)P_{MUT}-T_{STD}}{V_{STD}-P_{STD}-T_{MUT}}-1)-100\%[/math]
The standard uncertainty of measurement can be calculated by the following method:
[math]u(f_{MUT}=\sqrt{\sum(\frac{\partial f_{MUT}}{\partial xi})^2-(u(xi))^2}[/math]
Where:
xi is each measurement component (pressure, temperature, etc)
u(xi) is the standard uncertainty of each xi
[math]\frac{\partial f_{MUT}}{\partial xi}[/math]is the partial derivative of fMUT related to each xi[math]\frac{\partial f_{MUT}}{\partial xi}[/math]is the partial derivative of frelated to each x
A typical uncertainty value resulting from a measurement similar to the one described above, can be around 0,3%.
The same measurement philosophy can be used for high pressure measurements with natural gas as test medium. In this case the calculations are more complicated, since many more quantities affect the measurement (pressure, natural gas composition, etc).
In both cases, high or low pressure, air or natural gas, the calibration method must be well documented and validated, since gas meters are mainly used for billing processes. One way to achieve this is accreditation according to ISO .
Written by Sofia
1.1 This document outlines the requirements for the certification, recertification, calibration and use of working level gas measuring apparatus using bell provers up to 10 ft³ capacity. These measuring apparatus are used for the verification, reverification and/or compliance sampling of gas meters. Bell provers with a volumetric capacity greater than 10 ft³ must be processed for certification on an individual basis as determined by Measurement Canada.
1.2 This document is supported by the procedures set out in GS-ENG-09-01.1&#;Procedures and Worksheets for Calibrating and Certifying Gas Measuring Apparatus&#;Working Level Bell Provers pursuant to the Requirements of GS-ENG-09-01.
1.3 This certification document is considered as interim, as it does not fully incorporate the requirements of S-S-02&#;Measurement Uncertainty and Meter Conformity Evaluation Specifications. However, the determination of measurement uncertainty is subject to the guidelines in GS-ENG-09-04&#;Guidelines for the Determination of Measurement Uncertainty in Working Level Bell Provers&#;Correlation Method.
This document is issued pursuant to sections 7 and 8 of the Electricity and Gas Inspection Regulations. It has been produced under the delegated authority of the Senior Engineer, Gas Measurement, Measurement Canada for the purposes of setting out the requirements for the calibration, certification and use of gas measuring apparatus.
Christian Lachance, P. Eng.
Senior Engineer &#; Natural Gas Measurement
Engineering and Laboratory Services Directorate
Measurement Canada
4.1.1 These requirements apply immediately upon issue to all gas measuring apparatus utilizing bell prover displacement technology.
4.2.1 For measuring apparatus to be certified, all the requirements of this document must be evaluated and the results must meet the applicable requirements.
4.2.2 Gas measuring apparatus may be certified for testing any or all types of approved gas meters at test flow rates within the flow rate capacity of the local volumetric standard and the gas measuring apparatus.
4.2.3 The certificate issued by the designating authority must be valid for a period established by regulations for the gas measuring apparatus at the location where the calibration was completed. Any relocation or software, equipment or component replacements or modifications which affect the performance of the gas measuring apparatus require recertification of the gas measuring apparatus. The extent of the recertification is to be determined by the designating authority upon receipt of the notice referred to in clause 4.5.2(g) of this document.
Gas measuring apparatus or related accessories intended to perform statistical calculations of average error and standard deviation of a sample of gas meters for the purposes of verification, reverification or compliance sampling must do so pursuant to the requirements of a Measurement Canada-approved statistical sampling plan for the verification or reverification of gas meters.
The method of certification testing must be sufficient to ensure that the gas measuring apparatus will function accurately and reliably over the conditions to which it will be subjected. These conditions include, but are not limited to, ambient air temperature, meter proving air temperature, model of meter, condition of meter, test flow rates and modes of gas measuring apparatus operation. Where it has been determined analytically or empirically that the effect of a particular condition is not significant with respect to the accuracy of a specific type of gas measuring apparatus, the method of certification testing may, with the Senior Engineer's - Gas Measurement permission, be modified to take this evidence into account. If more than one method of meter proving is to be certified, the steps in sections 5.5.3, 5.5.4 and 5.5.5 must be performed using all meter proving methods requested.
The designating authority is responsible for:
The owner is responsible for:
The owner must provide to the designating authority a detailed statement of intended use of the gas measuring apparatus. The documentation provided must be sufficient to determine the capabilities of the gas measuring apparatus, its intended uses and all installation requirements. The intended use of the gas measuring apparatus must:
The minimum test volume must be as specified in Table 1 or the metric equivalent unless the owner or manufacturer can demonstrate that reducing the volume will not affect the performance of the apparatus.
Table 1: Minimum test volumes for bell provers Bell capacity Direct counting type Inferential type 2 ft3 2 ft3 0.5 ft3 5 ft3 2 ft3 0.5 ft3 10 f3 5 ft3 2 ft3The statement of intended use of the gas measuring apparatus must include:
5.1.1.1 The prover room ambient air temperature must be continuously maintained and monitored at ± 1 °C of the temperature chosen by the owner. The owner may change the temperature at any time during the period of the certification, but it must fall within a range of 22 °C ± 4 °C and meet the requirement of section 5.1.1.3.
5.1.1.2 The temperature of the prover room ambient air, the meter outlet air, the gas measuring apparatus bell outlet air and the prover oil must be within 0.5 °C of each other during all testing procedures and during any subsequent verification, reverification or compliance sample testing during the certification period.
5.1.1.3 Prior to and during certification testing, the prover room ambient air temperature must not vary by more than ± 1 °C and ± 0.5 °C over the previous twenty-four hour and four-hour periods, respectively.
5.2.1 New prover oil, when acquired for use in bell provers, must have the following properties:
5.2.2 The owner must ensure that specifications of oil purchased are met. The documentation supplied with regards to the prover oil must clearly indicate the source, brand name and batch number of the oil being used.
5.2.3 Where more than one prover has been filled with new oil from the same batch, only one representative oil sample from one of the provers needs to be tested to ensure the oil meets the specifications.
5.2.4 Prover oil must be tested annually and at the time of certification, at an approved laboratory or by the use of authorized procedures. The sample is to be drawn from the top of the prover tank.
5.2.5 The following American Society for Testing Materials (ASTM) test method specifications are applicable to testing oil for the stated properties.
Table 2: American Society for Testing Materials test methods applicable to testing oil Property ASTM test method specifications Viscosity D445: Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity). Relative density D: Standard Test Method for Density, Relative Density, or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer MethodThe gas measuring apparatus installation and operation must be verified for compliance with the manufacturer's installation instructions and Measurement Canada requirements. Where auxiliary equipment is attached or is to be attached to the bell, the counterweight wheel or its shaft or any other movable component of the gas measuring apparatus installation not specifically mentioned, the bell balance calibrations must be performed with the auxiliary equipment attached.
5.3.1.1 The components listed below must be checked to ensure that they are vertical. Installation of the components must be checked at least in two views spaced 90° from each other:
5.3.1.2 The bell components must be aligned such that all components will operate in the same plane of motion throughout the entire operating range of the bell.
5.3.2.1 The prover oil level must be checked at the start point and the maximum point of travel with the bell closed to atmosphere and the internal bell pressure adjusted to 2.00 ± 0.02 inches water column.
5.3.2.2 The sealant oil level must be measured and recorded when the bell is lowered to its maximum travel and open to atmosphere.
5.3.2.3 The prover oil level must be recorded and shown on the certificate issued by the designating authority together with the reference point.
5.3.3.1 The bell balance testing must commence at the start point used to start the proving operation and at points equal to 20, 40, 60 and 80 % of the intended range of travel of the bell and end at the maximum point of travel.
5.3.3.2 The bell must remain stationary at any and all points chosen for bell balance calibration.
5.3.4.1 Upon completion of the procedure set out in clause 5.3.3, the bell pressure must be adjusted, if required.
5.3.4.2 With the bell positioned within the range of bell travel, the main counter weight must be adjusted to achieve a bell pressure of 2.00 ± 0.02 inches water column.
5.3.5.1 The bell static pressure calibrations must commence at the start point and at points equal to 20, 40, 60 and 80 % of the intended range of bell travel and end at the maximum point of bell travel.
5.3.5.2 The bell static pressure at all calibrated points must be equal to 2.00 ± 0.02 inches water column.
5.3.6.1 The bell dynamic pressure calibrations must commence at the start point and at points equal to 20, 40, 60 and 80 % of the intended range of bell travel and end at the maximum point of bell travel.
5.3.6.2 The bell dynamic pressure at all calibrated points must be equal to 2.00 ± 0.02 inches water column as the bell descends at a rate not exceeding 8 inches per minute.
5.3.7.1.1 A system leak test must be conducted with all auxiliary equipment connected to the gas measuring apparatus. The piping of gas measuring apparatus must include a meter in the system leak test.
5.3.7.1.2 The system leak test must be conducted with the bell at a cardinal point near the bottom of the intended range of bell travel. The leak test time interval must be a minimum of 10 minutes during which the bell position must be monitored.
5.3.7.1.3 The position of the bell must not change during the system test.
5.3.7.1.4 When a gas measuring apparatus is equipped with an outlet control valve and the meter and associated piping up to the outlet control valve is pressurized, the entire system, including the outlet control valve, must be part of the system leak test.
5.3.7.2.1 The operational leak test procedure must be incorporated into the use of the gas measuring apparatus process and must be tested for both leak detection capability and repeatability.
5.3.7.2.2 Operational leak test procedures must be capable of detecting a leak of 0.25 cubic feet per hour at 2 inches of water column or greater using a leak test duration and applied pressure/vacuum designated by the owner. The operational leak test must be initiated three consecutive times to verify the reliability and repeatability of the process.
5.3.7.2.3 The owner must provide the leak test apparatus, calibrated to the local volumetric standard or another certified reference standard, for the purpose of the operational leak test.
5.3.8.1 The flow rate setting mechanism of the gas measuring apparatus must be tested at both the high and low load verification test points for each meter listed in the statement of intended use.
5.3.8.2 The flow rate mechanism must be capable of setting the flow rates to within the specifications of the nominal high load and low load verification test points for each meter listed in the statement of intended use.
5.3.8.3 The flow rate setting mechanism must be tested on the gas measuring apparatus using:
5.3.8.4 In the case of an adjustable flow rate mechanism, the flow rate mechanism calibration must be repeated six times at the high load flow rate and six times at the low load flow rate for each meter. In the case of fixed flow rate caps, the flow rate tests must be repeated three times at the high load flow rate and three times at the low load flow rate.
5.3.8.5 Each calculated flow rate must be within ± 5 % of the designated low and high load flow rates for the meter being tested.
If the gas measuring apparatus is equipped with a register ratio verification option, it must be verified. The register ratio option must be verified by utilizing both a correct and an incorrect model of register representing a metric and imperial meter designated in the statement of intended use to ensure that the system is capable of accurately detecting the correct register ratio.
Note: This optional equipment does not remove the dial test inspection requirement. Where an inspection is carried out using the direct counting method, the dial test is effectively addressed, since the proving is carried out directly off the test dial. Where an inspection is carried out using an inferential method, a dial test procedure must be developed by the contractor, and evaluated and approved by the Measurement Canada gas specialist.
Meters shown in the statement of intended use must be grouped according to either meter class or meter classification, depending on the method of counting used by the gas measuring apparatus. A transfer meter is chosen to represent each meter class or meter classification.
5.4.2.1 Transfer meters representative of meters in the various meter classes or meter classifications must be used to determine the percent error of the gas measuring apparatus by comparison to the local volumetric standard.
5.4.2.2 Transfer meters must be non-converting positive displacement gas meters.
5.4.2.3 Each transfer meter must be calibrated to possess an error within the range of -2 % and -3 % at low and high load flow rates, and a maximum difference between the low load error and the high load error (spread) of 0.5 or less.
5.4.2.4 Transfer meters must be acclimatized in the area of the gas measuring apparatus for a minimum period of four hours.
5.4.2.5 It is the responsibility of the owner to ensure that selected transfer meters are proven repeatable prior to use as transfer meters. The suggested method is as follows:
The selected meter is considered acceptable for use as a transfer meter provided that the percent error of each of the runs at the specified test flow rate is within ± 0.2 of the X-bar of percent errors for all six runs (see Table 3 for example).
Table 3: Determination of meter repeatability Run #1 Run #2 Run #3 Run #4 Run #5 Run #6 X-bar5.4.2.6 The flow rate of the local volumetric standard must be set to within ± 2 % of Qmax of the specified high and low load test points for the transfer meter to be tested. For example, the high load flow rate of a meter with a rated capacity of 180 cubic feet per hour would be within 257.4 cubic feet per hour to 264.6 cubic feet per hour and the low load flow rate would be 77.4 cubic feet per hour to 84.6 cubic feet per hour.
5.4.2.7 The flow rate of the gas measuring apparatus must be set to 145 % ± 5 % and 45 % ± 5 % of the badged flow rate of the transfer meter to be tested. The flow rate of the gas measuring apparatus must be set to within ± 5 % of Qmax of the specified high and low load test points for the transfer meter to be tested. For example, the high load flow rate of a meter with a rated capacity of 180 cubic feet per hour would be within 252 cubic feet per hour to 270 cubic feet per hour, and the low load flow rate would be 72 cubic feet per hour to 90 cubic feet per hour.
In order to test a direct counting gas measuring apparatus for the purpose of certification or recertification, a transfer meter must be chosen from each meter class listed in the statement of intended use to act as representative of the class.
In order to test an inferential gas measuring apparatus for the purpose of certification, a transfer meter of each meter classification listed in the statement of intended use must be tested. In the case of a scheduled recertification of an inferential gas measuring apparatus, a transfer meter representative of each meter class listed in the statement of intended use is chosen.
5.5.3.1 Volume correlation must be made to the local volumetric standard to determine whether the gas measuring apparatus may be certified for:
5.5.3.2 Volume correlations must be conducted at the low and high load flow rates of each meter being tested.
5.5.3.3 Volume correlations must be conducted with the gas measuring apparatus in the non-converting mode.
5.5.3.4 Testing of a gas measuring apparatus using a transfer meter must be completed on the same day that the transfer meter acceptability and proof errors were established with the local volumetric standard.
5.5.3.5 Each transfer meter must be proven six times with the gas measuring apparatus at both the low and high load flow rates of that transfer meter.
5.5.3.6 The percent error for each of the six runs must be within ± 0.2 of the X-bar of the percent errors of the meter as determined with the local volumetric standard at each flow rate.
5.5.3.7 The requirements of sections 5.5.3, 5.5.4 and 5.5.5 must be satisfied for each method of meter proving, as designated by the owner.
5.5.4.1 Volume correlations to determine the maximum detectable error must be completed with non-converting transfer meters of any one meter class, type or design set out in the statement of intended use. Transfer meters must be adjusted by the owner to register the following errors:
5.5.4.2 The transfer meters must be run six times with the gas measuring apparatus at the high load flow rates. The X-bar of the errors of the six runs must be used to determine compliance for maximum error detection. The gas measuring apparatus must be placed in non-converting mode.
5.5.4.3 The percent error of each transfer meter test, as determined with the gas measuring apparatus, must be within ± 0.2 of the X-bar of the percent errors as determined on the local volumetric standard.
5.5.5.1 Temperature differential mode correlations
5.5.5.2 Temperature converting mode correlations
6.1.1.1 The volume correlation of the transfer meters to the local volumetric standard must be performed:
6.1.1.2 The transfer meters used for the weekly volume correlation must be representative of the metric or imperial meter classifications of those meters which are to be verified, reverified or compliance tested that week.
6.1.1.3 The transfer meter must be run six times with the local volumetric standard at both the low and high load flow rates. The flow rate of the local volumetric standard must be set to 145 % ± 2 % and 45 % ± 2.0 % of the badged air flow rate of the transfer meter to be tested. The X-bar of the percent errors of these runs must be used to determine the average true errors. These values must be utilized during correlation of the gas measuring apparatus over the course of the next week.
6.1.1.4 Transfer meter performance must be tracked to ensure reliability and repeatability. Weekly errors greater than ± 0.2 for either the high or low load flow rate from the previous correlation to the local volumetric standard must be investigated and noted in the designated prover log book.
6.1.2.1 Volume correlation of the gas measuring apparatus must be performed:
6.1.2.2 For direct counting gas measuring apparatus, the transfer meters used must be representative of the metric or imperial meter class of those meters which are to be verified or reverified that day. For inferential gas measuring apparatus, the transfer meters used must be representative of the metric or imperial meter classification of those meters which are to be verified or reverified that day. Meters of any other classification must not be processed until the transfer meter representing that meter classification has been subjected to the daily volume correlation process. Daily volume correlations need not be performed if gas meters are not to be verified or reverified during that day.
6.1.2.3 Transfer meters must be run three times with the gas measuring apparatus at both the high load flow rate and low load flow rate. The low and high load flow rates of the gas measuring apparatus must be set to within 145 ± 5 % and 45 ± 5 % of the badged air rate of the transfer meter to be tested. The X-bars of the percent errors of these three runs must be used to determine the average true error, which must be within ± 0.2 of the percent error as established against the local volumetric standard within the previous one-week period.
6.1.2.4 Where the ± 0.2% allowable error tolerance has been exceeded, the steps below must be followed until the deficiency is resolved:
6.1.3.1 An operational leak detection sequence must be utilized prior to the final test sequence for all verification, reverification and compliance testing procedures.
6.1.3.2 The duration of the operational leak test must be as determined by the owner and specified for the test shown in section 5.3.7.2.
The owner of the gas measuring apparatus must have a sample of the prover oil tested annually and at the time of recertification for viscosity and relative density in accordance to the test methods requirement in section 5.2.5. Certificates of analysis must be made available to the designating authority upon request.
6.1.5.1 The prover room ambient air temperature must be continuously maintained and monitored at ± 1 °C of the temperature chosen by the owner. The chosen temperature may be changed by the owner at any time during the period of the certification, but must fall within a range of 22 °C ± 4 °C and meet the requirement of section 5.1.1.3.
6.1.5.2 The prover room ambient air temperature, the meter outlet air, the gas measuring apparatus bell outlet air temperature and the prover oil temperature must be within 0.5 °C of each other during all testing procedures and during any subsequent verification, reverification or compliance sample testing during the certification period.
6.1.5.3 Prior to and during all verification, reverification or compliance sample testing, the prover room ambient air temperature must not vary by more than ± 1 °C and 0.5 °C over the previous twenty-four hour and four-hour periods, respectively.
6.1.5.4 Temperature records must be retained for a time period of not less than three years.
6.1.6.1 The owner must perform routine maintenance as specified in the manufacturer's and owner's manuals. As a minimum, the maintenance and/or calibration of components and sensors must be performed annually.
6.1.6.2 The calibration of pressure, temperature and other sensors must be performed with a traceable standard.
6.1.6.3 Records of maintenance and calibrations must be maintained as part of the prover log book as per section 4.5.2(h).
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