S-G-03–Specifications for the approval of type of gas metering devices–Part 17

Category: Gas
Issue date:
Effective date:
Revision number: 3
Supersedes: S-G-03 (rev. 2)


Part 17: Compressed natural gas dispensers

Table of contents


1.0 Scope

This part of the Specifications applies to dispensers used in compressed natural gas (CNG) fuelling stations.

2.0 Unit requirements

Note: The requirements of Part 1, section 1.0 apply.

2.1 Units of measurement

The preferred unit of registration is the kilogram (kg) or the megajoule (MJ). If the commodity is registered in units of volume, that is the cubic foot (ft3) or cubic metre (m3), the volume must be converted to standard conditions.

3.0 Metrological requirements

Note: The following requirements of Part 1, section 2.0 apply:

  • 2.1 Rated operating conditions
  • 2.2 Flow rate characteristics
  • 2.3 Maximum permissible errors
  • 2.4 Weighted mean error
  • 2.5 Repeatability
  • 2.6 Working pressure
  • 2.7 Temperature
  • 2.12 Flow disturbance
  • 2.14 Different gases
  • 2.16 Supply voltage variation

3.1 Maximum permissible errors

The error on mass registrations must not exceed the maximum permissible errors (MPE) specified in Table 1 below.

Part 17, Table 1: Maximum permissible errors
Device MPE (% of the measured quantity value)
Coriolis mass flow meter (i.e. gas meter only) ± 1.0%
Dispenser (i.e. complete measuring system) ± 2.0%

3.2 Minimum measured quantity

The maximum value of the minimum measured quantity (MMQ) depends on the applications specified in Table 2 below.

Part 17, Table 2: Maximum value of the minimum measured quantity (MMQ)
Characteristics Standard application Heavy duty application Bulk application
Service pressure (either or)
  • 8300 kPa (1200 psi)
  • 16500 kPa (2400 psi)
  • 20700 kPa (3000 psi)
  • 24800 kPa (3600 psi)
  • 20700 kPa (3000 psi)
  • 24800 kPa (3600 psi)
  • 20700 kPa (3000 psi)
  • 24800 kPa (3600 psi)
Number of delivery hose 1 or 2 1 or 2 1 or more
Diameter of delivery hose 1/4" up to 3/4" 1/2" and up 3/4" and up
Receptacle/nozzle type
(CSA/ANSI NGV 1-2017)
P12, P24, P30, P36 P30HD, P36HD P30HD, P36HDFootnote 17-1
Type of vehicle E.g. light and medium duty natural gas powered vehicles E.g. heavy duty natural gas powered vehicles l.e. tube trailers
Expected minimum tank size 40 L 100 L 4500 L
Expected fill rate capacity Up to 50 kg/min Up to 100 kg/min 100 kg/min and upFootnote 17-2
Maximum value of MMQ 2 kg 5 kg 150 kg

3.3 Price to be paid

The registration of price to be paid must agree to within ± 1 cent with the value obtained by multiplying the unit price by the gas measured quantity.

3.4 Zero-setting

Where a mechanical register is used with a dispenser, the error in resetting the mechanical register to zero must not exceed 3° of movement from an indicator mark.

3.5 Presetting

The following requirements apply:

  • Where the quantity of gas to be measured is preset, the quantity of gas delivered by the dispenser must correspond at least to the preset quantity ± 1 minimum increment set forth in 4.1 according to the display of the dispenser before the flow is automatically stopped.
  • Where the price to be paid is preset, the quantity of gas delivered by the dispenser must correspond at least to the preset price ±1 cent according to the display at the dispenser before the flow is automatically stopped.

4.0 Technical requirements

Note: The following requirements of Part 1, section 3.0 apply:

  • 3.1 Design, composition and construction
  • 3.4 Case
  • 3.6.2 Unidirectional flow measurement
  • 3.7 Indication
  • 3.10 Software

4.1 Gas quantity indicating device

A dispenser must be equipped with at least one indicating device displaying the quantity of gas measured. The capacity of the display must comply with one of the following requirements:

  • not be less than 99.999 kg with a resolution of at least 0.001 kg;
  • 9999.9 MJ with a resolution of at least 0.1 MJ; or
  • 99.999 std m3 with a resolution of at least 0.001 std m3(9999.9 std ft3 with a resolution of at least 0.1 std ft3).

Furthermore, the indicating device must be resettable to zero.

4.2 Price indicating device

A dispenser must be equipped with at least one price indicating device which displays both the unit price and the price to be paid, and must comply with the following requirements:

  • Unit price:

    The display must be adjustable with a resolution of 0.1 cents per unit of metered quantity.

  • Price to be paid:

    The capacity of the display must not be less than $99.999 with a resolution of 1 cent and it must be resettable to zero.

4.3 Electronic indicating devices

The following requirements apply:

  • Electronic indicating devices must either:
    • automatically display all segments for at least 0.5 seconds and blank for at least 0.5 seconds after a register is reset to zero and before another delivery is started to allow an operator to detect a segment that either indicates continuously or does not indicate; or
    • incorporate an automatic self-testing system which checks the correct operation of all display elements prior to commencing a delivery and on detection of a fault prevents further use of the register.
  • The measured gas quantity, unit price and price to be paid must remain displayed for at least five minutes after a delivery is completed or until the next transaction is initiated or the current transaction is finalized.

4.4 Interlocks

4.4.1 Indicating devices

A dispenser must be designed so that it's inoperable after a transaction is completed until the resettable indicating devices are reset to zero by means of an automatic interlock.

4.5 Systematic deviation

The design of the dispenser must ensure that the measured quantity is delivered. In particular, if the hose and piping downstream of the meter is likely to be depressurized between two deliveries this must lead for instance to systematic correction or repressurizing before a zero condition is reached at the start of a new delivery.

Whatever the operating principle is (repressurizing or not), in particular whatever constitutes the hose or the transfer point, in the worst operating conditions, the error of the residual mass which is measured, though not delivered and no correction is made by the dispenser, must be less than or equal to the MPE at the rated MMQ for the dispenser.

4.6 Ticket printer

4.6.1 Ticket information

Where a ticket printer forms part of or is used in conjunction with a dispenser, the ticket must carry the following information related to the current transaction:

  • Name of the contractor and address of the location where the dispenser is installed;
  • An identification number for the Coriolis mass flow meter, or if there is only one meter, the identification number of the dispenser;
  • The gas measured quantity and units indicated on the indicating device;
  • Unit price and price to be paid indicated on the price indicating device;
  • Date that the delivery was made;
  • An automatically advanced sequential sales number.
4.6.2 Ticket printer interlock

Where a ticket printer is provided with a dispenser, an interlock must be incorporated such that a ticket is printed for every transaction.

4.7 Dispenser configuration

The following requirements apply:

  • Dispensers intended for refuelling from both sides must have indicating devices on both sides.
  • No means must be provided by which any measured gas can be diverted downstream of the meter during a filling operation.

4.8 Reverse flow prevention

There must be means provided to prevent flow of gas from the vessel back through the dispenser in the event that the vessel to be refilled has a higher initial pressure than the dispenser delivery pressure.

4.9 Power mains failure

Dispensers which operate from the mains power supply must, in the event of a power outage, either:

  1. continue to operate satisfactorily for:
    • 24 hours where a back-up supply which automatically recharges upon restoration of the power is used; or
    • 7 days where any other type of backup supply is used; or
  2. retain programming and metering information for the applicable period as specified in 4.9(a), and must be capable, upon demand, of displaying the gas measured quantity, unit price and price to be paid at any time up to 15 minutes after the power outage.

4.10 Transfer point

The following requirements apply:

  1. A dispenser must incorporate a transfer point located downstream of the meter.
  2. Two or more delivery transfer points may be permanently installed and operated simultaneously or alternately provided so that any diversion of gas to receptacles other than the intended receiving receptacles must not be readily accomplished or readily apparent.

    Note: Such means include, for example, physical barriers, visible valves or indications that make it clear which transfer points are in operation, and explanatory signs, if necessary.

  3. When only one transfer point can be used during a delivery, and after the nozzle of the transfer point has been placed back on its slot, the next delivery must be inhibited until the indicating device has been reset to zero.
  4. When two or more transfer points can be used simultaneously or alternately, and after the utilized nozzles of the transfer points have been placed back on their slots, the next delivery must be inhibited until the indicating device has been reset to zero. Moreover, by design, the requirement in 4.10 (b) must be fulfilled.

5.0 Marking requirements

Notes: The following requirements of Part 1, section 4.0 apply:

  • 4.1 Permanency and legibility
  • 4.2
    • (a) Departmental approval number
    • (b) Manufacturer's name or registered trademark
    • (c) Model or type designation
    • (d) Serial number
    • (e) Ambient temperature range, where less than -30 °C to 40 °C
    • (f) Pmin (where applicable) and Pmax
    • (g) Qmax
    • (j) Gas temperature range for which the errors ≤ MPE
  • 4.9 External power supply
  • 4.10 Software
  • 4.12 Inspection number
  • 4.13 Verification marks

According to the characteristics of the dispenser, the following requirements may also apply:

  • 4.3 Bar codes or quick response codes
  • 4.14 Operating information

5.1 Different flow rate ranges

Where the flow rate range is not the same for all hoses, the flow rate range for each group of hoses must be marked.

5.2 Components

The following requirements apply:

  • Each Coriolis mass flow meter, remote electronics unit and printer (where it is located on or in the dispenser) must bear a nameplate showing the following markings of the component required in Part 1, subsection 4.2:
    • 4.2 (b) Manufacturer's name or registered trademark
    • 4.2 (c) Model or type designation
    • 4.2 (d) Serial number
  • Nameplates must be clearly visible with the cover(s) removed.
  • Each Coriolis mass flow meter must comply with the marking requirements of Part 6, section 5.0.

5.3 Minimum measured quantity

The MMQ must be marked.

6.0 Sealing requirements

Note: The following requirements of Part 1, section 5.0 apply:

  • 5.1 General
  • 5.2 Electronic gas metering devices

6.1 Assembly

Where a dispenser comprises more than one separate assembly, the interconnecting cables and tubing must be so arranged as to be capable of being sealed in a manner which will prevent replacement of any assembly without breaking a seal.

6.2 Provision for price adjustment

There must be provision for adjusting the unit price of the commodity being sold without the necessity of breaking a seal.

6.3 Security of price adjustment

Access to the price-setting mechanism must be limited to authorized personnel by provision of a lock and key arrangement or equivalent.

6.4 Price

It must not be possible to change the unit price during calculation of the price to be paid for any given delivery.

6.5 Ticket printer

Where a ticket printer forms part of or is used in conjunction with a dispenser, the ticket printer must be designed so that a jammed ticket can be removed without breaking any inspection seals.

7.0 Administrative requirements

Note: The requirements of Part 1, section 6.0 apply.

8.0 Performance test requirements

Note: Test conditions and performance tests can be obtained by contacting MC.

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