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Field inspection manual—volumetric measuring devices

Category: Volume
Part: 4-STP
Section: 27
Publication date:
Revision number: 4

Part 4, section 27—Specialised test procedure—Gravimetric testing of meters registering in units of volume

Application

This gravimetric procedure can be used to test any type of approved meter indicating in units of volume. This procedure will be used in conjunction with the appropriate density determination procedure as documented in the volumetric field inspection manual Part 4, STP-41 "Specialized Test Procedures: Procedure for Density Determination".

Note: The accuracy and suitability of any density measurement are dependent upon the density sample being representative of the product measured during the meter evaluation. The sample must be homogeneous and identical to the product used during testing. The sample must not contain any entrained air and must have reached a stable temperature. Slurries, suspensions or mixtures will not be suitably homogeneous and therefore, this procedure cannot be used.

Purpose

This procedure is used to determine the accuracy of liquid measuring systems using gravimetric test methods and to assess their compliance with the applicable limits of error prescribed by the Weights and Measures Act and Regulations, or other applicable terms and conditions.

References

R.262, R.263, R265, R.267(2)(3), R.268(5)(6) of the Weights and Measures Regulations, Terms and Conditions for the Approval of Coriolis Liquid Meters, section 4.1.1.

Equipment

  • A product reference scale suitable to hold the delivery vessel when full of product. Consult the table in Appendix 1 or the Measurement Canada (MC) minimum test quantity (MTQ) spreadsheet for selection of the appropriate scale and/or test volume.
  • A delivery vessel of sufficient capacity and constructed with materials suitable for the product collected.
  • Local standards of mass in sufficient size and quantity to establish the suitability of the product reference scale and the density sample scale if used.
  • A certified thermometer with 0.1 °C graduations or less, appropriate for thermal well insertion.
  • Authorized volume correction tables appropriate for the product and/or MC-authorized spreadsheets or software applications.
  • Suitable density determination equipment (density scale and pycnometer or hydrometer).
  • A method to move product from the delivery vessel back to the storage tank (e.g. pump, etc.).

Procedure

Determine the product density

The key component of any gravimetric test of a liquid product, when metered in units of volume, is the determination of the product density. In simple terms, the dispensed volume of the meter under test is compared to the mass reading obtained from the product reference scale used for the tests. The volume of product on the reference scale is calculated with the use of the following basic formula:

Volume=mass÷density

The sample density for the product is determined using the appropriate procedure as outlined in the volumetric field inspection manual, Part 4, STP-41 "Specialized Test Procedures—Procedure for Density Determination".

Determine the suitability of the product reference scale

The accuracy, repeatability, linearity and sensitivity of the scale must be determined using local standards of mass before and after inspecting a particular measuring system. Refer to STP-45 for scale performance testing procedures. Only scales that meet the requirements of STP-45 may be used for the gravimetric testing of liquid measuring systems.

Determine the minimum test quantity to be delivered for the test

The relationship between the required MTQ and the scale's minimum interval must be such that the expanded uncertainty (k=2) of the delivered volume is less than or equal to 1⁄3 of the limit of error (LOE) for the meter under test.

The MTQ for each run must meet the minimum load size requirements, as per the appropriate reference tables in Appendix 1. In order to meet the uncertainty requirement for the measurement as stipulated above, these tables include values that relate the MTQ for the particular device LOE to the graduation size of the scale used for density determination and the large reference scale.

For many liquid measuring systems, the MTQ is prescribed in the Weights and Measures Regulations as a function of the meter size, type or application and in-service LOE. For example:

  • R.265: Applicable to dispensers for motor fuel, refuellers for small aircraft and boats, meters for use in measuring automotive or petroleum liquids not mentioned elsewhere.
    While there are no legislated MTQs for devices subject to R.265, MC policy is to use test volumes not less than the following:
    • 5 L for pistol-style lube oil dispensers (60 ml in-service LOE)
    • 20 L for dispensers with an approved maximum flow rate of ≤ 90 lpm (100 ml in-service LOE)
  • R.266(2): Applicable to positive displacement (PD) meters 2½" (65 mm) or smaller, including truck-mounted meters for use in measuring automotive or petroleum liquids, chemicals, including diesel exhaust fluid (DEF), and liquid fertilizers.
    • 225 L min. to 900 L max. (0.25% (¼%) in-service LOE)
  • R.266(3): Applicable to PD meters 3" (75 mm) or larger, including truck-mounted meters for use in measuring automotive or petroleum liquids, chemicals, including DEF, and liquid fertilizers.
    • 1350 L minimum (0.25% (¼%) in-service LOE)
  • R.267(2): Applicable to PD meters 2½" (65 mm) or smaller, including truck-mounted meters for use in measuring lube oils, bunker oil and other products of high viscosity.
    • 225 L min. to 900 L max. (0.5% (½%) in-service LOE)
  • R.267(3): Applicable to PD meters 3" (75 mm) or larger, including truck-mounted meters, lube oils
    • 1350 L minimum (0.375% (3⁄8%) in-service LOE)
  • R.268(5): Applicable to liquefied petroleum gas (LPG) dispensers for auto propane
    • 25-45 L (2% in-service LOE)
    • >45 L (1% in-service LOE)
  • R.268(6): Applicable to LPG meters 1" (25 mm) or larger
    • 100-200 L (1% in-service LOE)
    • >200 L (0.75% in-service LOE)

Note: Where one (1) minute of flow at the meter's maximum rated flow rate is greater than the quantity prescribed above, the required load is a quantity of product equivalent to at least one (1) minute of flow for all meters covered by R.266 and R.267.

The minimum measured quantity (MMQ) for any Coriolis meter is listed on the corresponding meter notice of approval (NOA) issued by Approval and Calibration Services Laboratory. It should be noted that LOEs can be applied to Coriolis metering assemblies without using the one-minute flow provision, as the terms and conditions document does not prescribe the time requirement.

In most cases, the MTQ requirement for proceeding with gravimetric testing of liquids will be the largest of:

  • the legislated minimum requirement (either Weights and Measures Regulations or terms and conditions),
  • the amount of product to account for one (1) minute of flow at the maximum operating flow rate (where applicable), and
  • the test load stipulated in the tables in Appendix 1.

Example 1: 2" truck-mounted PD meter

Product

Lube oil

Density: 880 kg/m³

Device

Maximum actual flow rate: 260 lpm

Applicable LOE: 0.5%

Test equipment

Density reference scale

  • capacity ≤ 500 g
  • graduation ≤ 0.1 g

Product reference scale (10,000 division scale)

  • capacity ≥ 1000 kg
  • graduation ≤ 0.1 kg (100 g)

For practical purposes, it is preferable to perform the tests with a minimum amount of product. To accomplish this, a product reference scale with the smallest graduations possible should be selected. For example, if a 1000 kg x 0.1 kg reference scale (10,000 divisions) was selected, the MTQ would be:

  1. regulatory requirement: 0.5% (in-service LOE, R.267(2) = MTQ 225 L)
  2. performance requirement: 260 L (one minute at maximum operating flow rate)
  3. MTQ: 225 L (0.5% LOE, Appendix 1 or MTQ spreadsheet)

The revised MTQ requirement is equal to 260 L (the larger of 225 L or 260 L), which corresponds to the volume of product metered in one (1) minute at the meter's maximum actual flow rate. The product reference scale would similarly require performance testing to a weight indication equivalent to the weight of the containment vessel plus approximately 260 L/230 kg of product. See STP-45 for more information.

Example 2: 1" truck-mounted Coriolis meter

Product

LPG

Density: 506 kg/m³

Device

Maximum actual flow rate: 380 lpm

Accuracy class (LOE): 1.0 (1.0%)

MMQ: 15 kg or 15 L

Test equipment

Certified hydrometer (standard)

  • range: suitable for product density
  • graduation ≤ 0.5 kg/m³

Product reference scale (10,000 divisions)

  • capacity ≥ 200 kg
  • graduation ≤ 0.02 kg (20 g)
Minimum test quantity requirements
  1. 75 L (requirement from the terms and conditions or NOA, 5 × MMQ)
  2. 159 L (test load Table 8 for a reference scale interval 0.02 kg and 1% LOE)

Despite the fact that the meter's maximum operating flow rate is 380 lpm, Coriolis meters do not have a requirement for one (1) minute of flow at maximum operating flow rate as with other types of meters. In this case, the MTQ would be 159 L. The terms and conditions stipulate LOE applications in terms of any quantity in excess of the MMQ.

The containment vessel would have a capacity large enough to safely contain this amount of product, and the large product reference scale would require performance testing to a weight indication equivalent to the weight of the container plus approximately 159 L/80 kg of LPG. See STP-45 for more information.

Example 3: ½" skid-mounted Coriolis meter

Product

DEF

Density: 1100 kg/m³

Device

Maximum actual flow rate: 90 lpm

Accuracy class (LOE): 0.3 (0.3%)

MMQ: 5 kg/5 L

Test equipment

Density reference scale

  • capacity ≤ 3 kg
  • graduation ≤ 0.01 g

Product reference scale (6000 divisions)

  • capacity ≤ 300 kg
  • graduation ≤ 0.05 kg (50 g)
Minimum test quantity requirements
  1. 25 L (terms and conditions or NOA, 5 × MMQ)
  2. 195 L (test load Table 7: reference scale interval 0.05 kg)

The MTQ required to gravimetrically test the device with the equipment listed above would be 195 L. Certified mass standards would be required in order to performance test the product reference scale to a weight indication equivalent to the weight of the containment vessel plus approximately 195 L/177 kg of product. See STP-45 for more information.

Test thermowell and product temperature requirements

For gravimetric testing results to be valid, the product temperature, as it flows through the meter, must be known. This is required in order to correct the indicated volume for thermal expansion or contraction of the product with respect to the density sample taken for the product separately.

The product temperature is recorded during test runs and is obtained by inserting the certified thermometer into the automatic temperature compensator's thermowell, which, ideally, is located adjacent to the meter temperature transducer for devices equipped with an automatic temperature compensator. For systems which do not incorporate automatic temperature compensation, a similarly installed test thermowell (i.e., in accordance with SVM-2) must be made available to facilitate gravimetric testing procedures. Positioning the temperature probe in the flowing product the discharge location is not suitable for gravimetric testing purposes, as it introduces a potentially significant temperature variance from the actual metered temperature.

The product supply and piping temperatures need to be stabilized prior to conducting the test runs. Refer to the appropriate device STP for stabilization requirements.

Test procedure for liquid meters

  1. Run appropriate volume of product, as determined above (or in Appendix 1), at the required flow rate for the test. Record the liquid temperature at the meter, as indicated by the thermometer standard, at approximately 25%, 50%, 75% and 95% of the test volume. Correct each of the four temperature readings for errors as stated on the thermometer calibration certificate. Calculate the average of the four (4) corrected readings. This is the corrected flowing temperature (Tm) in the meter for the test run.
  2. Record the gross volume indicated by the meter and the weight indicated by the scale. Correct the scale reading with the scale correction factor (SCF) calculated during the scale accuracy tests, as per STP-45.
    The mass of the delivered product may now be calculated as:
    Mass(kg)=scale indication (kg)×SCF
  3. Calculate the known test quantity (KTQ) in litres using the mass obtained from the corrected scale indication divided by the corrected sample density value (rho15) in kg/L.
    KTQ=Mass(kg)÷rho_15
  4. Determine the correction for the temperature of the product in the meter (Ctlm) for the delivered product using the sample density (see Part 4-STP, section 41 "Specialized Test Procedures: Procedure for Density Determination") at the corrected flowing temperature (Tm) obtained during the delivery. Use the appropriate API table 54 (ASTM-IP table 54 for LPG, natural gas and asphalts) or MC-authorized equivalents.

    Note: For high vapour pressure products, pressure compensation back to the equilibrium vapour pressure will also be required (Cplm). For low vapour pressure products, Cplm can be assumed to be equal to 1.0 and ignored. The procedure for LPG dispensers allows for an assumed Cplm = 1.0020 to be used when a pressure gauge is not available at the meter.

  5. Calculate the corrected volume from the meter (CVm) in litres by multiplying the gross indicated volume of the meter (IVm) in litres by the temperature correction factor (Ctlm) and the pressure correction factor (Cplm) for the delivered product as it passes through the meter.

    CVm=IV_m×Ctl_m×Cpl_m

  6. Calculate the actual meter error for the test run.

    Meter error (%)=((CVm-KTQ)÷KTQ)×100

  7. Drain the containment vessel, if necessary, and repeat for the required number of tests as per the inspection procedure outline for the specific measuring system under test. Ensure that the reference scale zero reading remains stable throughout all test runs. If the reference scale exhibits zero-return errors during any of the product runs, the results become invalid and testing may be restarted only if the reference scale errors are corrected.
  8. Once all the necessary test runs are completed, verify the product reference scale performance as per STP-45. If the scale does not meet all the requirements, the test results obtained are not acceptable, and must be redone. The scale must meet all the requirements before and after testing for the results to be acceptable.

Testing of single flow rate devices

Typically, devices such as lube oil dispenser pistols are operated at a single flow rate. If this is the case, it is only necessary to conduct accuracy and repeatability tests at the flow rate under normal conditions of use. The flow rates for these devices are governed by the type of pumps used in the particular installation, but must remain within approved maximum and minimum flow rates for the device.

To test single flow rate devices, performance tests are conducted at the normal and observed operating rate of the device.

Interpretation of results

Liquid meters indicating in units of volume

For all device types, the resulting meter error determined by gravimetric methods must be within the prescribed LOEs specific to the meter under test. The repeatability allowance for three consecutive test runs is 2/5 of the in-service LOE.

Note: Please contact your Volumetric Specialist to obtain the latest copy of the applicable worksheets.

Revisions

The purpose of revision 4 was to:

  • modify procedures and formulae to account for the removal of air buoyancy calculations.
  • generalize the procedure to incorporate all types of liquid meters registering in units of volume.
  • add test thermowell requirement for gravimetric testing of liquid products.
  • remove Appendix 1 and reference the new standard scale performance test procedure.
  • add minimum test load selection tables for some common applications in Appendix 1.
  • remove Appendix 3.
  • renumber the remaining appendices.

The purpose of revision 3 was to:

  • modify the equation to calculate the corrected mass of the delivered product under section c) of "Testing Lube Oil Meters" and in Appendix 4.
  • add an equation to determine liquid density of the flowing product under section d) of "Testing Lube Oil Meters" and in Appendix 4.
  • modify an equation to calculate and the KTQ under section e) of "Testing Lube Oil Meters" and in Appendix 4.

The purpose of revision 2 was to:

  • completely revise the procedure to ensure the relationship between the minimum required test quantity and the scale's minimum interval is such that the expanded uncertainty (k=2) of the delivered volume is less than or equal to 1⁄3 of the LOE for a particular meter under test.
  • include four new appendices: Scale Accuracy and Calibration Checks, Minimum Required Test Loads, Example Calculations and Gravimetric Testing of Liquid Measuring Systems Work Sheet.

The purpose of revision 1 was to add device types 50.10, 52.10-12 and 52.20-22 to the list of device types identified in the title line.

Appendix 1—Minimum test quantities

The relationship between the minimum required test quantity and the scale's minimum interval must be such that the expanded uncertainty (k=2) of the delivered volume is less than or equal to 1/3 of the LOE for the particular meter under testFootnote 1. However, in all circumstances, the MTQ must not be less than that prescribed by the Weights and Measures Regulations or the Terms and Conditions for the Approval of Coriolis Liquid Meters.

The following tables are excerpts from tables developed by MC engineering and are representative of some standard liquid product installations that are gravimetrically tested. Test quantities listed are dependent upon the minimum scale intervals (graduations) for the density reference scale and product reference scale, the type of device and the applicable LOE. For Coriolis meters, the test quantities listed are dependent upon the minimum scale intervals of the product reference scale and the density sample scale or the minimum graduation of the hydrometer standard, as well as the type of device and applicable LOE.

Some MC test equipment, such as the mobile LPG gravimetric provers, has been designed with specific combinations of reference scale graduations and density determination equipment. The tables below may not give the same test quantities as are normally used with this equipment. As this equipment has been authorized for use in testing under specific conditions, no further evaluation of the MTQ need be done by the inspector.

If gravimetric testing of a product not listed in the following tables is desired, contact your Volumetric Specialist or MC engineering for more information.

Minimum test quantities in litres for some common applications

Table 1a – R.266(2) PD meters ≤ 65 mm
Low viscosity liquids – LOE 0.25%, interval = 0.01 g
Reference scale interval (kg) Minimum test quantity when density scale interval = 0.01 g
0.01 225 L
0.02 225 L
0.05 225 L
0.10 385 L
0.20 770 L
0.50 1923 L
1 3846 L
2 7692 L
5 19 230 L
10 38 460 L
20 76 920 L
Table 1b – R.266(2) PD meters ≤ 65 mm
Low viscosity liquids – LOE 0.25%, interval = 0.1 g
Reference scale interval (kg) Minimum test quantity when density scale interval = 0.1 g
0.01 225 L
0.02 225 L
0.05 225 L
0.10 434 L
0.20 867 L
0.50 2166 L
1 4332 L
2 8664 L
5 21 660 L
10 43 319 L
20 86 638 L

Product density: 1100 kg/m³
(example: diesel exhaust fluid)

Table 2a – R.266(3) PD meters ≥ 75 mm
Low viscosity liquids – LOE 0.25%, interval = 0.01 g
Reference scale interval (kg) Minimum test quantity when density scale interval = 0.01 g
0.01 1350 L
0.02 1350 L
0.05 1350 L
0.10 1350 L
0.20 1350 L
0.50 1923 L
1 3846 L
2 7692 L
5 19 230 L
10 38 460 L
20 76 920 L
Table 2b – R.266(3) PD meters ≥ 75 mm
Low viscosity liquids – LOE 0.25%, interval = 0.1 g
Reference scale interval (kg) Minimum test quantity when density scale interval = 0.1 g
0.01 1350 L
0.02 1350 L
0.05 1350 L
0.10 1350 L
0.20 1350 L
0.50 2166 L
1 4332 L
2 8664 L
5 21 660 L
10 43 319 L
20 86 638 L

Product density: 1100 kg/m³
(example: diesel exhaust fluid)

Table 3a – R.267(2) PD meters ≤ 65 mm
High viscosity liquids – LOE 0.50% interval = 0.01 g
Reference scale interval (kg) Minimum test quantity when density scale interval = 0.01 g
0.01 225 L
0.02 225 L
0.05 225 L
0.10 225 L
0.20 410 L
0.50 1025 L
1 2049 L
2 4098 L
5 10 243 L
10 20 486 L
20 40 972 L
Table 3b – R.267(2) PD meters ≤ 65 mm
High viscosity liquids – LOE 0.50%, interval = 0.1 g
Reference scale interval (kg) Minimum test quantity when density scale interval = 0.1 g
0.01 225 L
0.02 225 L
0.05 225 L
0.10 225 L
0.20 423 L
0.50 1057 L
1 2114 L
2 4227 L
5 10 566 L
10 21 131 L
20 42 261 L

Product density: 880 kg/m³
(example: lube oil)

Table 4a – R.267(3) PD meters ≥ 75 mm
High viscosity liquids – LOE 0.375%, interval = 0.01 g
Reference scale interval (kg) Minimum test quantity when density scale interval = 0.01 g
0.01 1350 L
0.02 1350 L
0.05 1350 L
0.10 1350 L
0.20 1350 L
0.50 1440 L
1 2880 L
2 5759 L
5 14 396 L
10 28 791 L
20 57 581 L
Table 4b – R.267(3) PD meters ≥ 75 mm
High viscosity liquids – LOE 0.375%, interval = 0.1 g
Reference scale interval (kg) Minimum test quantity when density scale interval = 0.1 g
0.01 1350 L
0.02 1350 L
0.05 1350 L
0.10 1350 L
0.20 1350 L
0.50 1534 L
1 3067 L
2 6134 L
5 15 334 L
10 30 668 L
20 61 335 L

Product density: 880 kg/m³
(example: lube oil)

Table 5 – R.268(5) LPG meters < 25 mm
≥ 45 L test quantity – LOE 1.0%
Reference scale interval (kg) Minimum test quantity when hydrometer
graduation ≤ 0.5 kg/m³
0.01 50 L
0.02 50 L
0.05 200 L
0.10 500 L
0.20 1584 L
0.50 3958 L
1 7916 L
2 15 831 L
5 39 577 L
10 79 154 L
20 158 307 L

Product density: 500-510 kg/m³
(example: LPG)

Note: The first four values in this table have been adjusted to reflect standard practice.

Table 6 – R.268(6) LPG meters ≥ 25 mm
≥ 200 L test quantity – LOE 0.75%
Reference scale interval (kg) Minimum test quantity when hydrometer graduation ≤ 0.5 kg/m³
0.01 200 L
0.02 200 L
0.05 200 L
0.10 914 L
0.20 1828 L
0.50 4572 L
1 9144 L
2 18 288 L
5 45 722 L
10 91 443 L
20 182 887 L

Product density: 500-510 kg/m³
(example: LPG)

Note: The first three values in this table have been adjusted to reflect standard practice.

Table 7a – Coriolis terms and conditions, section 4.1.1
All other liquids – Class 0.3 (0.30%), interval = 0.01 g
Reference scale interval (kg) Minimum test quantity when density scale interval = 0.01 g
0.01 39 L
0.02 78 L
0.05 195 L
0.10 389 L
0.20 778 L
0.50 1944 L
1 3887 L
2 7774 L
5 19 434 L
10 38 868 L
20 77 736 L
Table 7b – Coriolis terms and conditions, section 4.1.1
All other liquids – Class 0.3 (0.30%), interval = 0.1 g
Reference scale interval (kg) Minimum test quantity when density scale interval = 0.1 g
0.01 44 L
0.02 88 L
0.05 220 L
0.10 440 L
0.20 879 L
0.50 2196 L
1 4391 L
2 8781 L
5 21 953 L
10 43 905 L
20 87 809 L

Product density: 880 kg/m³
(example: lube oil)

Table 8 – Coriolis terms and conditions, section 4.1.1
Compressed liquefied gases – Class 1 (1.0%)
Reference scale interval (kg) Minimum test quantity when hydrometer graduation ≤ 0.5 kg/m³
0.01 80 L
0.02 159 L
0.05 396 L
0.10 792 L
0.20 1584 L
0.50 3958 L
1 7916 L
2 15 831 L
5 39 577 L
10 79 154 L
20 158 307 L

Product density: 500-510 kg/m³
(example: liquefied natural gas)

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