Handbook 44 – 2022 3.39. Hydrogen Gas-Measuring Devices Code

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Table of Contents

Page

Section 3.39. Hydrogen Gas-Measuring Devices............................................................ 3-143

A. Application ................................................................................................................................................ 3-143

A.1. General..............................................................................................................................................3-143

A.2. Exceptions.........................................................................................................................................3-143

A.3. Additional Code Requirements.........................................................................................................3-143

A.4. Type Evaluation................................................................................................................................3-143

S. Specifications............................................................................................................................................. 3-143

S.1. Indicating and Recording Elements. .................................................................................................3-143

S.1.1. Indicating Elements ............................................................................................................3-143

S.1.2. Vehicle Fuel Dispensers .....................................................................................................3-143

S.1.3. Units....................................................................................................................................3-143

S.1.4. Value of Smallest Unit........................................................................................................3-144

S.2. Operating Requirements. ..................................................................................................................3-144

S.2.1. Return to Zero.....................................................................................................................3-144

S.2.2. Indicator Reset Mechanism.................................................................................................3-144

S.2.3. Provision for Power Loss....................................................................................................3-144

S.2.4. Display of Unit Price and Product Identity.........................................................................3-144

S.2.5. Money-Value Computations...............................................................................................3-145

S.2.6. Recorded Representations, Point of Sale Systems..............................................................3-145

S.2.7. Indication of Delivery.........................................................................................................3-145

S.2.8. Automatic Timeout – Pay-At-Vehicle Fuel Dispensers.......................................................3-145

S.3. Design of Measuring Elements and Measuring Systems. .................................................................3-145

S.3.1. Maximum and Minimum Flow-Rates.................................................................................3-145

S.3.2. Adjustment Means. .............................................................................................................3-145

S.3.3. Provision for Sealing...........................................................................................................3-145

S.3.4. Automatic Density Correction. ...........................................................................................3-147

S.3.5. Pressurizing the Discharge Hose.........................................................................................3-147

S.3.6. Zero-Set-Back Interlock, Retail Vehicle Fuel Devices.......................................................3-147

S.4. Discharge Lines and Valves..............................................................................................................3-147

S.4.1. Diversion of Measured Product. .........................................................................................3-147

S.4.2. Directional Flow Valves. ....................................................................................................3-147

S.4.3. Other Valves. ......................................................................................................................3-147

S.5. Markings...........................................................................................................................................3-147

S.5.1. Location of Marking Information; Hydrogen-Fuel Dispensers. .........................................3-148

S.6. Printer. ..............................................................................................................................................3-148

S.6.1. Printed Receipt....................................................................................................................3-148

S.7. Totalizers for Vehicle Fuel Dispensers.............................................................................................3-148

S.8. Minimum Measured Quantity...........................................................................................................3-148

N. Notes........................................................................................................................................................... 3-149

N.1. Minimum Measured Quantity...........................................................................................................3-149

N.2. Test Medium.....................................................................................................................................3-149

N.3. Test Drafts.........................................................................................................................................3-149

N.4. Tests..................................................................................................................................................3-149

N.4.1. Master Meter (Transfer) Standard Test...............................................................................3-149

N.4.2. Gravimetric Tests................................................................................................................3-149

N.4.3. PVT Pressure Volume Temperature Test. ..........................................................................3-149
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N.5. Minimum Measured Quantity...........................................................................................................3-149

N.6. Testing Procedures............................................................................................................................3-149

N.6.1. General................................................................................................................................3-149

N.6.2. Repeatability Tests..............................................................................................................3-150

N.7. Density..............................................................................................................................................3-150

T. Tolerances.................................................................................................................................................. 3-150

T.1. Tolerances, General. .........................................................................................................................3-150

T.2. Tolerances.........................................................................................................................................3-150

T.3. Repeatability. ....................................................................................................................................3-150

T.4. Tolerance Application on Test Using Transfer Standard Test Method.............................................3-150

T.5. Tolerance Application in Type Evaluation Examinations for Devices. ............................................3-150

UR. User Requirements ................................................................................................................................... 3-151

UR.1. Selection Requirements. ...................................................................................................................3-151

UR.1.1. Computing-Type Device; Retail Dispenser. .......................................................................3-151

UR.1.2. Discharge Hose-Length. .....................................................................................................3-151

UR.1.3. Minimum Measured Quantity.............................................................................................3-151

UR.2. Installation Requirements. ................................................................................................................3-151

UR.2.1. Manufacturer’s Instructions................................................................................................3-151

UR.2.2. Discharge Rate....................................................................................................................3-151

UR.2.3. Low-Flow Cut-Off Valve. ..................................................................................................3-151

UR.3. Use of Device....................................................................................................................................3-152

UR.3.1. Unit Price and Product Identity for Retail Dispensers. .......................................................3-152

UR.3.2. Vehicle-mounted Measuring Systems Ticket Printer..........................................................3-152

UR.3.3. Printed Ticket......................................................................................................................3-152

UR.3.4. Steps After Dispensing. ......................................................................................................3-152

UR.3.5. Return of Indicating and Recording Elements to Zero. ......................................................3-152

UR.3.6. Return of Product to Storage, Retail Hydrogen Gas Dispensers.........................................3-152

UR.3.7. Conversion Factors. ............................................................................................................3-152
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Section 3.39. Hydrogen Gas-Measuring Devices 

The status of Section 3.39. Hydrogen Gas-Measuring Devices was changed from “tentative” to “permanent” effective 

January 1, 2020.

(Added 2010) (Amended 2019)

A. Application

A.1. General. – This code applies to devices that are used for the measurement of hydrogen gas in the vapor state 

used as a vehicle fuel.

A.2. Exceptions. – This code does not apply to:

(a) Devices used solely for dispensing a product in connection with operations in which the amount dispensed 

does not affect customer charges.

(b) The wholesale delivery of hydrogen gas.

(c) Devices used for dispensing a hydrogen gas with a hydrogen fuel index lower than 99.97 % and 

concentrations of specified impurities that exceed level limitsin the latest version of SAE International J2719.

(d) Systems that measure pressure, volume, and temperature with a calculating device to determine the mass of 

gas accumulated in or discharged from a tank of known volume.

A.3. Additional Code Requirements. – In addition to the requirements of this code, Hydrogen Gas-Measuring 

Devices shall meet the requirements of Section 1.10. General Code.

A.4. Type Evaluation. – The National Type Evaluation Program (NTEP) will accept for type evaluation only those 

devices that comply with all requirements of this code.

S. Specifications

S.1. Indicating and Recording Elements.

S.1.1. Indicating Elements. – A measuring assembly shall include an indicating element that continuously 

displays measurement results relative to quantity and total price. Indications shall be clear, definite, accurate, and 

easily read under normal conditions of operation of the device.

S.1.2. Vehicle Fuel Dispensers. – A hydrogen gas dispenser used to fuel vehicles shall be of the computing 

type and shall indicate the mass, the unit price, and the total price of each delivery.

S.1.3. Units.

S.1.3.1. Units of Measurement. – Deliveries shall be indicated and recorded in kilograms and decimal

subdivisions thereof.

S.1.3.2. Numerical Value of Quantity-Value Divisions. – The value of an interval (i.e., increment or

scale division) shall be equal to:

(a) 1, 2, or 5; or

(b) a decimal multiple or submultiple of 1, 2, or 5.
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Examples: quantity-value divisions may be 10, 20, 50, 100; or 0.01, 0.02, 0.05; or 0.1, 0.2, or 0.5;

etc.

S.1.3.3. Maximum Value of Quantity-Value Divisions. – The maximum value of the quantity-value 

division shall not be greater than 0.5% of the minimum measured quantity.

S.1.3.4. Values Defined. – Indicated values shall be adequately defined by a sufficient number of figures, 

words, symbols, or combinations thereof. A display of “zero” shall be a zero digit for all displayed digits to 

the right of the decimal mark and at least one to the left.

S.1.4. Value of Smallest Unit. – The value of the smallest unit of indicated delivery, and recorded delivery if 

the device is equipped to record, shall not exceed the equivalent of: 

(a) 0.001 kg on devices with a marked maximum flow rate of 30 kg/min or less; or

(b) 0.01 kg on devices with a marked maximum flow rate of more than 30 kg/min.

S.2. Operating Requirements.

S.2.1. Return to Zero. 

(a) The primary indicating and the primary recording elements, if the device is equipped to record, shall be 

provided with a means for readily returning the indication to zero either automatically or manually.

(b) It shall not be possible to return primary indicating elements, or primary recording elements, beyond the 

correct zero position.

S.2.2. Indicator Reset Mechanism. – The reset mechanism for the indicating element shall not be operable 

during a delivery. Once the zeroing operation has begun, it shall not be possible to indicate a value other than the 

latest measurement, or “zeros” when the zeroing operation has been completed.

S.2.3. Provision for Power Loss. 

S.2.3.1. Transaction Information. – In the event of a power loss, the information needed to complete 

any transaction in progress at the time of the power loss (such as the quantity and unit price, or sales price) 

shall be determinable for at least 15 minutes at the dispenser or at the console if the console is accessible to 

the customer. 

S.2.3.2. User Information. – The device memory shall retain information on the quantity of fuel 

dispensed and the sales price totals during power loss.

S.2.4. Display of Unit Price and Product Identity. 

S.2.4.1. Unit Price. – A computing or money-operated device shall be able to display on each face the 

unit price at which the device is set to compute or to dispense.

S.2.4.2. Product Identity. – A device shall be able to conspicuously display on each side the identity of 

the product being dispensed.

S.2.4.3. Selection of Unit Price. – When a product is offered for sale at more than on unit price through 

a computing device, the selection of the unit price shall be made prior to delivery using controls on the device 

or other customer-activated controls. A system shall not permit a change to the unit price during delivery of 

a product.
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S.2.4.4. Agreement Between Indications. – All quantity, unit price, and total price indications within a 

measuring system shall agree for each transaction.

S.2.5. Money-Value Computations. – A computing device shall compute the total sales price at any singlepurchase unit price for which the product being measured is offered for sale at any delivery possible within either 

the measurement range of the device or the range of the computing elements, whichever is less.

S.2.5.1. Auxiliary Elements. – If a system is equipped with auxiliary indications, all indicated money 

value and quantity divisions of the auxiliary element shall be identical with those of the primary element. 

S.2.5.2. Display of Quantity and Total Price. – When a delivery is completed, the total price and quantity 

for that transaction shall be displayed on the face of the dispenser for at least 5 minutes or until the next 

transaction is initiated by using controls on the device or other user-activated controls. 

S.2.6. Recorded Representations, Point of Sale Systems. – A printed receipt shall be available through a 

built-in or separate recording element for transactions conducted with point-of-sale systems or devices activated 

by debit cards, credit cards, and/or cash. The printed receipt shall contain the following information for products 

delivered by the dispenser:

(a) the total mass of the delivery;

(b) the unit price;

(c) the total computed price; and

(d) the product identity by name, symbol, abbreviation, or code number.

S.2.7. Indication of Delivery. – The device shall automatically show on its face the initial zero condition and 

the quantity delivered (up to the nominal capacity).

S.2.8. Automatic Timeout – Pay-At-Vehicle Fuel Dispensers. – Once a vehicle fuel dispenser has been 

authorized, it must deauthorize within two minutes if not activated. Reauthorization of the vehicle fuel dispenser 

must be performed before any product is delivered. If the time limit to deauthorize the vehicle fuel dispenser is 

programmable, it shall not accept an entry greater than two minutes. 

[Nonretroactive as of January 1, 2020]

(Added 2019)

S.3. Design of Measuring Elements and Measuring Systems.

S.3.1. Maximum and Minimum Flow-Rates. – The ratio of the maximum to minimum flow-rates specified 

by the manufacturer for devices measuring gases shall be 10:1 or greater.

S.3.2. Adjustment Means. – An assembly shall be provided with means to change the ratio between the 

indicated quantity and the quantity of gas measured by the assembly. A bypass on the measuring assembly shall 

not be used for these means.

S.3.2.1. Discontinuous Adjusting Means. – When the adjusting means changes ratio between the 

indicated quantity and the quantity of measured gas in a discontinuous manner, the consecutive values of the 

ratio shall not differ by more than 0.1 %.

S.3.3. Provision for Sealing. – For devices and systems in which the configuration or calibration parameters 

can be changed by use of a removable digital storage device, security shall be provided for those parameters as 

specified in G-S.8.2. Devices and Systems Adjusted Using Removable Digital Storage Devices. For parameters 

adjusted using other means, the following applies.
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Adequate provision shall be made for an approved means of security (e.g., data change audit trail) or physically 

applying security seals in such a manner that no adjustment can be made of:

(a) each individual measurement element;

(b) any adjustable element for controlling delivery rate when such rate tends to affect the accuracy of 

deliveries;

(c) the zero-adjustment mechanism; and

(d) any metrological parameter that detrimentally affects the metrological integrity of the device or system.

When applicable, the adjusting mechanism shall be readily accessible for purposes of affixing a security seal. Audit 

trails shall use the format set forth in Table S.3.3. Categories of Device and Methods of Sealing.

(Amended 2019)

Table S.3.3.

Categories of Device and Methods of Sealing

Categories of Device Method of Sealing

Category 1: No remote configuration capability. Seal by physical seal or two event counters: one for

calibration parameters and one for configuration 

parameters.

Category 2: Remote configuration capability, but 

access is controlled by physical hardware. 

The device shall clearly indicate that it is in the remote 

configuration mode and record such message if 

capable of printing in this mode or shall not operate 

while in this mode.

The hardware enabling access for remote 

communication must be on-site. The hardware must 

be sealed using a physical seal or an event counter for 

calibration parameters and an event counter for 

configuration parameters. The event counters may be 

located either at the individual measuring device or at

the system controller; however, an adequate number of 

counters must be provided to monitor the calibration 

and configuration parameters of the individual devices 

at a location. If the counters are located in the system 

controller rather than at the individual device, means 

must be provided to generate a hard copy of the 

information through an on-site device.

Category 3: Remote configuration capability access 

may be unlimited or controlled through a software 

switch (e.g., password).

The device shall clearly indicate that it is in the 

remote configuration mode and record such message 

if capable of printing in this mode or shall not 

operate while in this mode.

An event logger is required in the device; it must 

include an event counter (000 to 999), the parameter 

ID, the date and time of the change, and the new value 

of the parameter. A printed copy of the information 

must be available on demand through the device or 

through another on-site device. The information may 

also be available electronically. The event logger shall 

have a capacity to retain records equal to 10 times the 

number of sealable parameters in the device, but not 

more than 1000 records are required. (Note: Does not 

require 1000 changes to be stored for each parameter.)

(Amended 2016)
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S.3.4. Automatic Density Correction.

(a) An automatic means to determine and correct for changes in product density shall be incorporated in any 

hydrogen gas-measuring system where measurements are affected by changes in the density of the 

product being measured.

(b) Volume-measuring devices with automatic temperature compensation used to measure hydrogen gas as 

a vehicle fuel shall be equipped with an automatic means to determine and correct for changes in product 

density due to changes in the temperature, pressure, and composition of the product. 

S.3.5. Pressurizing the Discharge Hose. – The discharge hose for hydrogen gas shall automatically pressurize 

to a pressure equal to or greater than the receiving vessel prior to the device beginning to register the delivery. 

The indications shall not advance as a result of the initial pressurization or the purging/bleeding of the discharge 

hose.

S.3.6. Zero-Set-Back Interlock, Retail Vehicle Fuel Devices. 

(a) A device shall be constructed so that:

(1) when the device is shut-off at the end of a delivery an automatic interlock prevents a subsequent 

delivery until the indicating element and recording elements, if the device is equipped and activated

to record, have been returned to their zero positions; and

(2) it shall not be possible to return the discharge nozzle to its start position unless the zero set back 

interlock is engaged or becomes engaged.

(b) For systems with more than one:

(1) dispenser supplied by a single measuring element, an effective automatic control valve in each 

dispenser prevents product from being delivered until the indicating elements on that dispenser are 

in a correct zero position; or 

(2) hose supplied by a single measuring element, effective automatic means must be provided to prevent 

product from being delivered until the indicating element(s) corresponding to each hose are in a 

correct zero position.

S.4. Discharge Lines and Valves.

S.4.1. Diversion of Measured Product. – No means shall be provided by which any measured product can be 

diverted from the measuring device. 

S.4.2. Directional Flow Valves. – If a reversal of flow could result in errors that exceed the tolerance for the 

minimum measured quantity, a valve or valves or other effective means, automatic in operation (and equipped 

with a pressure limiting device, if necessary) to prevent the reversal of flow shall be properly installed in the 

system. (Also see N.1. Minimum Measured Quantity.)

S.4.3. Other Valves. – Check valves and closing mechanisms that are not used to define the measured quantity 

shall have relief valves (if necessary) to dissipate any abnormally high pressure that may arise in the measuring 

assembly.

S.5. Markings. – A measuring system shall be conspicuously, legibly, and indelibly marked with the following 

information:

(a) pattern approval mark (i.e., type approval number);
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(b) name and address of the manufacturer or his trademark and, if required by the weights and measures 

authority, the manufacturer's identification mark in addition to the trademark;

(c) model designation or product name selected by the manufacturer;

(d) nonrepetitive serial number;

(e) the accuracy class of the device as specified by the manufacturer consistent with Table T.2. Accuracy Classes 

and Tolerances for Hydrogen-Gas Measuring Devices;

(f) maximum and minimum flow rates in kilograms per unit of time;

(g) maximum working pressure;

(h) applicable range of ambient temperature if other than – 10 °C to + 50 °C;

(i) minimum measured quantity; and

(j) product limitations (such as fuel quality), if applicable.

S.5.1. Location of Marking Information; Hydrogen-Fuel Dispensers. – The marking information required 

in General Code, paragraph G S.1. Identification shall appear as follows:

(a) within 60 cm (24 in) to 150 cm (60 in) from the base of the dispenser;

(b) either internally and/or externally provided the information is permanent and easily read; and accessible 

for inspection; and

(c) on a portion of the device that cannot be readily removed or interchanged (i.e., not on a service access 

panel).

The use of a dispenser key or tool to access internal marking information is permitted for retail hydrogenmeasuring devices.

S.6. Printer. – When an assembly is equipped with means for printing the measured quantity, the printed 

information must agree with the indications on the dispenser for the transaction and the printed values shall be clearly 

defined.

S.6.1. Printed Receipt. – Any delivered, printed quantity shall include an identification number, the time and 

date, and the name of the seller. This information may be printed by the device or pre-printed on the ticket.

S.7. Totalizers for Vehicle Fuel Dispensers. – Vehicle fuel dispensers shall be equipped with a nonresettable

totalizer for the quantity delivered through each separate measuring device.

S.8. Minimum Measured Quantity. – The minimum measured quantity shall satisfy the conditions of use of the 

measuring system as follows:

(a) Measuring systems having a maximum flow rate less than or equal to 4 kg/min shall have a minimum 

measured quantity not exceeding 0.5 kg.

(b) Measuring systems having a maximum flow rate greater than 4 kg/min but not greater than 12 kg/min shall 

have a minimum measured quantity not exceeding 1.0 kg.
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N. Notes

N.1. Minimum Measured Quantity. – The minimum measured quantity shall be specified by the manufacturer.

N.2. Test Medium. – The device shall be tested with the product commercially measured except that, in a type 

evaluation examination, hydrogen gas as specified in NIST Handbook 130 shall be used.

N.3. Test Drafts. – The minimum test shall be one test draft at twice the declared minimum measured quantity and 

one test draft at approximately five times the minimum measured quantity or 4 kg, whichever is greater. More tests 

may be performed over the range of normal quantities dispensed. (Also see T.3. Repeatability.)

The test draft shall be made at flows representative of that during normal delivery. The pressure drop between the 

dispenser and the proving system shall not be greater than that for normal deliveries. The control of the flow (e.g., 

pipework or valve(s) size, etc.) shall be such that the flow of the measuring system is maintained within the range 

specified by the manufacturer.

N.4. Tests.

N.4.1. Master Meter (Transfer) Standard Test. – When comparing a measuring system with a calibrated 

transfer standard, the minimum test shall be one test draft at the declared minimum measured quantity and one 

test draft at approximately ten times the minimum measured quantity or 1 kg, whichever is greater. More tests 

may be performed over the range of normal quantities dispensed.

N.4.1.1. Verification of Master Metering Systems. – A master metering system used to verify a hydrogen 

gas-measuring device shall be verified before and after the verification process. A master metering system 

used to calibrate a hydrogen gas-measuring device shall be verified before starting the calibration and after 

the calibration process.

N.4.2. Gravimetric Tests. – The weight of the test drafts shall be equal to at least twice the amount delivered 

by the device at the declared minimum measured quantity and one test draft at approximately five times the 

minimum measured quantity or 4 kg, whichever is greater. More tests may be performed over the range of normal 

quantities dispensed. 

N.4.3. PVT Pressure Volume Temperature Test. – The minimum test with a calibrated volumetric standard 

shall be one test draft at twice the declared minimum measured quantity and one test draft at approximately five

times the minimum measured quantity or 4 kg, whichever is greater. More tests may be performed over the range 

of normal quantities dispensed.

N.5. Minimum Measured Quantity. – The device shall be tested for a delivery equal to the declared minimum 

measured quantity when the device is likely to be used to make deliveries on the order of the declared minimum 

measured quantity.

N.6. Testing Procedures.

N.6.1. General. – The device or system shall be tested under normal operating conditions of the dispenser.

The test draft shall be made at flows representative of that during normal delivery. The pressure drop between 

the dispenser and the proving system shall not be greater than that for normal deliveries. The control of the flow 

(e.g., pipework or valve(s) size, etc.) shall be such that the flow of the measuring system is maintained within the 

range specified by the manufacturer.
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N.6.2. Repeatability Tests. – Tests for repeatability should include a minimum of three consecutive test drafts 

of approximately the same size and be conducted under controlled conditions where variations in factors are 

reduced to minimize the effect on the results obtained. When conducting the tests, the discharge rates shall be 

within the minimum and maximum discharge rates as marked by the manufacturer.

(Amended 2019)

N.7. Density. – Temperature and pressure of hydrogen gas shall be measured during the test for the determination 

of density or volume correction factors when applicable. For the thermophysical properties of hydrogen the following 

publications shall apply: for density calculations at temperatures above 255 K and pressures up to 120 MPa, a simple 

relationship may be used that is given in the publication of Lemmon et al., J. Res. NIST, 2008. Calculations for a 

wider range of conditions and additional thermophysical properties of hydrogen are available free of charge online at 

the “NIST Chemistry WebBook, NIST Standard Reference Database Number 69” (webbook.nist.gov/chemistry), or 

available for purchase from NIST as the computer program NIST Standard Reference Database 23 “NIST Reference 

Fluid Thermodynamic and Transport Properties Database (REFPROP): Version 10.0” (www.nist.gov/srd/refprop). 

These calculations are based on the reference Leachman, J.W., Jacobsen, R.T, Lemmon, E.W., and Penoncello, S.G. 

“Fundamental Equations of State for Parahydrogen, Normal Hydrogen, and Orthohydrogen" published in the Journal 

of Physical and Chemical Reference Data (www.nist.gov/publications/fundamental-equations-stateparahydrogen-normal-hydrogen-and-orthohydrogen?pub_id=832374).

T. Tolerances

T.1. Tolerances, General.

(a) The tolerances apply equally to errors of underregistration and errors of overregistration.

(b) The tolerances apply to all products at all temperatures measured at any flow rate within the rated measuring 

range of the device.

T.2. Tolerances. – The tolerances for hydrogen gas measuring devices are listed in Table T.2. Accuracy Classes 

and Tolerances for Hydrogen Gas-Measuring Devices. (Proposed tolerance values are based on previous work with 

compressed gas products and will be confirmed based on performance data evaluated by the U.S. National Work 

Group.)

Table T.2.

Accuracy Classes and Tolerances for Hydrogen Gas-Measuring Devices

Accuracy Class

Application or Commodity Being 

Measured

Acceptance 

Tolerance

Maintenance 

Tolerance

7.0 Hydrogen gas as a vehicle fuel 5.0 % 7.0 %

(Amended 2016)

T.3. Repeatability. – When multiple tests are conducted at approximately the same flow rate and draft size, the 

range of the test results for the flow rate shall not exceed 40 % of the absolute value of the maintenance tolerance and 

the results of each test shall be within the applicable tolerance. Also see N.6.2. Repeatability Tests.

(Amended 2019)

T.4. Tolerance Application on Test Using Transfer Standard Test Method. – To the basic tolerance values that 

would otherwise be applied, there shall be added an amount equal to two times the standard deviation of the applicable 

transfer standard when compared to a basic reference standard.

T.5. Tolerance Application in Type Evaluation Examinations for Devices. – For type evaluation examinations, 

the tolerance values shall apply under the following conditions:
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(a) at any temperature and pressure within the operating range of the device, and

(b) for all quantities greater than the minimum measured quantity.

UR. User Requirements

UR.1. Selection Requirements.

UR.1.1. Computing-Type Device; Retail Dispenser. – A hydrogen gas dispenser used to refuel vehicles shall 

be of the computing type and shall indicate the mass, the unit price, and the total price of each delivery.

UR.1.2. Discharge Hose-Length. – The length of the discharge hose on a retail fuel dispenser:

(a) shall not exceed 4.6 m (15 ft) unless it can be demonstrated that a longer hose is essential to permit 

deliveries to be made to receiving vehicles or vessels; 

(b) shall be measured from its housing or outlet of the discharge line to the inlet of the discharge nozzle; and

(c) shall be measured with the hose fully extended if it is coiled or otherwise retained or connected inside a 

housing.

An unnecessarily remote location of a device shall not be accepted as justification for an abnormally long hose.

UR.1.3. Minimum Measured Quantity.

(a) The minimum measured quantity shall be specified by the manufacturer. 

(b) The minimum measured quantity appropriate for a transaction may be specified by the weights and 

measures authority. A device may have a declared minimum measured quantity smaller than that 

specified by the weights and measures authority; however, the device must perform within the 

performance requirements for the declared or specified minimum measured quantity up to deliveries at 

the maximum measurement range.

(c) The minimum measured quantity shall satisfy the conditions of use of the measuring system as follows:

(1) measuring systems having a maximum flow rate less than or equal to 4 kg/min shall have a minimum 

measured quantity not exceeding 0.5 kg; and

(2) measuring systems having a maximum flow rate greater than 4 kg/min but not greater than 

12 kg/min shall have a minimum measured quantity not exceeding 1.0 kg.

UR.2. Installation Requirements.

UR.2.1. Manufacturer’s Instructions. – A device shall be installed in accordance with the manufacturer’s 

instructions, and the installation shall be sufficiently secure and rigid to maintain this condition.

UR.2.2. Discharge Rate. – A device shall be installed so that after initial equalization the actual maximum 

discharge rate will not exceed the rated maximum discharge rate. Automatic means of flow regulation shall be 

incorporated in the installation if necessary.

UR.2.3. Low-Flow Cut-Off Valve. – If a measuring system is equipped with a programmable or adjustable 

"low-flow cut-off" feature:
3.39. Hydrogen Gas-Measuring Devices Code Handbook 44 – 2022

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This publication is available free of charge from: https://doi.org/10.6028/NIST.HB.44-2022

(a) the low-flow cut-off value shall not be set at flow rates lower than the minimum operating flow rate 

specified by the manufacturer on the measuring device; and

(b) the system shall be equipped with flow control valves which prevent the flow of product and stop the 

indicator from registering product flow whenever the product flow rate is less than the low-flow cut-off

value.

UR.3. Use of Device.

UR.3.1. Unit Price and Product Identity for Retail Dispensers. – The unit price at which the dispenser is 

set to compute shall be conspicuously displayed or posted on the face of a retail dispenser used in direct sale.

UR.3.2. Vehicle-mounted Measuring Systems Ticket Printer.

UR.3.2.1. Customer Ticket. – Vehicle-mounted measuring systems shall be equipped with a ticket printer 

which shall be used for all sales where product is delivered through the device. A copy of the ticket issued 

by the device shall be left with the customer at the time of delivery or as otherwise specified by the customer.

UR.3.2.2. Ticket in Printing Device. – A ticket shall not be inserted into a device equipped with a ticket 

printer until immediately before a delivery is begun, and in no case shall a ticket be in the device when the 

vehicle is in motion while on a public street, highway, or thoroughfare.

UR.3.3. Printed Ticket. – The total price, the total quantity of the delivery, and the price per unit shall be 

printed on any ticket issued by a device of the computing type and containing any one of these values.

UR.3.4. Steps After Dispensing. – After delivery to a customer from a retail dispenser:

(a) the device shall be shut-off at the end of a delivery, through an automatic interlock that prevents a 

subsequent delivery until the indicating elements and recording elements, if the device is equipped and 

activated to record, have been returned to their zero positions; and

(b) the discharge nozzle shall not be returned to its start position unless the zero set-back interlock is engaged 

or becomes engaged by the act of disconnecting the nozzle or the act of returning the discharge nozzle. 

UR.3.5. Return of Indicating and Recording Elements to Zero. – The primary indicating elements (visual), 

and the primary recording elements shall be returned to zero immediately before each delivery. 

UR.3.6. Return of Product to Storage, Retail Hydrogen Gas Dispensers. – Provisions at the site shall be 

made for returning product to storage or disposing of the product in a safe and timely manner during or following 

testing operations. Such provisions may include return lines, or cylinders adequate in size and number to permit 

this procedure.

UR.3.7. Conversion Factors. – Established correction values. (Also see references in N.7. Density.) shall be 

used whenever measured hydrogen gas is billed. All sales shall be based on kilograms.