Handbook 44 - 2007 3.34. Cryogenic Liquid-Measuring Devices 

Section 3.34. Cryogenic Liquid-Measuring Devices 

A. Application

A.1. - This code applies to devices used for the measurement of cryogenic liquids such as, but not limited to oxygen, 

nitrogen, hydrogen, and argon. 

(Amended 1986 and 1995) 

A.2. - This code does not apply to the following: 

(a) Devices used for dispensing liquefied petroleum gases (for which see Sec. 3.32; Code for Liquefied Petroleum 

Gas and Anhydrous Ammonia Liquid-Measuring Devices). 

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

not affect customer charges. 

(c) Devices used solely for dispensing liquefied natural gas. 

(d) Mass flow meters (see Sec. 3.37. Code for Mass Flow Meters). 

(Added 1994) 

A.3. - See also Sec. 1.10; General Code requirements. 

S. Specifications 

S.1. Design of Indicating and Recording Elements and of Recorded Representations.

S.1.1. Primary Elements.

S.1.1.1. General. - A device shall be equipped with a primary indicating element and may also be equipped 

with a primary recording element. 

S.1.1.2. Units. - A device shall indicate and record, if equipped to record, its deliveries in terms of: kilograms 

or pounds; liters or gallons of liquid at the normal boiling point of the specific cryogenic product; cubic meters 

(cubic feet) of gas at a normal temperature of 21 °C (70 °F) and an absolute pressure of 101.325 kPa 

(14.696 psia); or decimal subdivisions or multiples of the measured units cited above. 

(Amended 2002) 

S.1.1.3. 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) for small delivery devices 

(1) 1 L 

(2) 0.1 gal 

(3) 1 kg 

(4) 1 lb 

(5) 0.1 m3 of gas 

(6) 10 ft3 of gas 

(b) for large delivery devices 

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3.34. Cryogenic Liquid-Measuring Devices Handbook 44 - 2007 

(1) 10 L 

(2) 1 gal 

(3) 10 kg 

(4) 10 lb 

(5) 1 m3

 of gas 

(6) 100 ft3 of gas 

(Amended 2002) 

S.1.1.4. Advancement of Indicating and Recording Elements. - Primary indicating and recording elements 

shall be susceptible to advancement only by the normal operation of the device. However, a device may be 

cleared by advancing its elements to zero, but only if: 

(a) the advancing movement, once started, cannot be stopped until zero is reached, or 

(b) in the case of indicating elements only, such elements are automatically obscured until the elements 

reach the correct zero position. 

S.1.1.5. Return to Zero. - Primary indicating and recording elements shall be readily returnable to a definite 

zero indication. Means shall be provided to prevent the return of primary indicating elements and of primary 

recording elements beyond their correct zero position. 

S.1.2. Graduations.

S.1.2.1. Length. - Graduations shall be so varied in length that they may be conveniently read. 

S.1.2.2. Width. - In any series of graduations, the width of a graduation shall in no case be greater than the 

width of the minimum clear interval between graduations, and the width of main graduations shall be not more 

than 50 % greater than the width of subordinate graduations. Graduations shall in no case be less than 0.2 mm 

(0.008 in) in width. 

S.1.2.3. Clear Interval Between Graduations. - The clear interval shall be no less than 1.0 mm (0.04 in). If 

the graduations are not parallel, the measurement shall be made: 

(a) along the line of relative movement between the graduations at the end of the indicator, or 

(b) if the indicator is continuous, at the point of widest separation of the graduations. 

(See also S.1.3.6.) 

S.1.3. Indicators.

S.1.3.1. Symmetry. - The index of an indicator shall be symmetrical with respect to the graduations, at least 

throughout that portion of its length associated with the graduations. 

S.1.3.2. Length. - The index of an indicator shall reach to the finest graduations with which it is used, unless the 

indicator and the graduations are in the same plane, in which case the distance between the end of the indicator 

and the ends of the graduations, measured along the line of the graduations, shall be not more than 1.0 mm 

(0.04 in). 

S.1.3.3. Width. - The width of the index of an indicator in relation to the series of graduations with which it is 

used shall be not greater than: 

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Handbook 44 - 2007 3.34. Cryogenic Liquid-Measuring Devices 

(a) the width of the narrowest graduation* , and 

[*Nonretroactive as of January 1, 2002]

(Amended 2001) 

(b) the width of the minimum clear interval between graduations. 

When the index of an indicator extends along the entire length of a graduation, that portion of the index of the 

indicator that may be brought into coincidence with the graduation shall be of the same width throughout the 

length of the index that coincides with the graduation. 

S.1.3.4. Clearance. - The clearance between the index of an indicator and the graduations shall in no case be 

more than 1.5 mm (0.06 in). 

S.1.3.5. Parallax. - Parallax effect shall be reduced to the practicable minimum. 

S.1.3.6. Travel of Indicator. - If the most sensitive element of the primary indicating element uses an indicator 

and graduations, the relative movement of these parts corresponding to the smallest indicated value shall be not 

less than 0.5 mm (0.20 in). 

S.1.4. Computing-Type Device.

S.1.4.1. Printed Ticket. - Any printed ticket issued by a device of the computing type on which there is printed 

the total computed price shall have printed clearly thereon also the total quantity of the delivery and the price per 

unit. 

S.1.4.2. Money-Value Computations. - Money-value computations shall be of the full-computing type in 

which the money value at a single unit price, or at each of a series of unit prices, shall be computed for every 

delivery within either the range of measurement of the device or the range of the computing elements, whichever 

is less. Value graduations shall be supplied and shall be accurately positioned. The total price shall be computed 

on the basis of the quantity indicated when the value of the smallest division indicated is equal to or less than the 

values specified in S.1.1.3. 

S.1.4.3. Money Values, Mathematical Agreement. - Any digital money-value indication and any recorded 

money value on a computing type device shall be in mathematical agreement with its associated quantity 

indication or representation to within 1 cent of money value. 

S.2. Design of Measuring Elements.

S.2.1. Vapor Elimination. - A measuring system shall be equipped with an effective vapor eliminator or other 

effective means to prevent the measurement of vapor that will cause errors in excess of the applicable tolerances. 

(See Section T. Tolerances) 

S.2.2. Directional Flow Valves. - A valve or valves or other effective means, automatic in operation, to prevent the 

reversal of flow shall be installed in or adjacent to the measuring device. 

(Amended 1978) 

S.2.3. Maintenance of Liquid State. - A device shall be so designed that the product being measured will remain in 

a liquid state during passage through the device. 

S.2.4. Automatic Temperature or Density Compensation. - A device shall be equipped with automatic means for 

adjusting the indication and/or recorded representation of the measured quantity of the product, to indicate and/or 

record in terms of: kilograms or pounds; or liters or gallons of liquid at the normal boiling point of the specific 

cryogenic product; or the equivalent cubic meters (cubic feet) of gas at a normal temperature of 21 ΕC (70 ΕF) and 

an absolute pressure of 101.325 kPa (14.696 lb/in2

 absolute). When a compensator system malfunctions, the 

indicating and recording elements may indicate and record in uncompensated volume if the mode of operation is 

clearly indicated, e.g., by a marked annunciator, recorded statement, or other obvious means*.

[*Nonretroactive as of January 1, 1992]

(Amended 1991 and 2002) 

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3.34. Cryogenic Liquid-Measuring Devices Handbook 44 - 2007 

S.2.5. Provision for Sealing. - Adequate provision shall be made for an approved means of security (e.g., data 

change audit trail) or for physically applying a security seal in such a manner that requires the security seal to be 

broken before an adjustment or interchange may be made of: 

(a) any measuring or indicating element, 

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

(c) any automatic temperature or density compensating system, and 

(d) any metrological parameter that will affect the metrological integrity of the device or system. 

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

[Audit trails shall use the format set forth in Table S.2.5.]* 

[*Nonretroactive as of January 1, 1995] 

(Amended 2006) 

Table S.2.5. Categories of Device and Methods of Sealing 

Category 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 through the device or through another on-site 

device. The event logger shall have a capacity to retain 

records equal to ten 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.)

[Nonretroactive as of January 1, 1995] 

(Table Added 2006) 

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Handbook 44 - 2007 3.34. Cryogenic Liquid-Measuring Devices 

S.3. Design of Discharge Lines and Discharge Line Valves.

S.3.1. Diversion of Measured Liquid. - No means shall be provided by which any measured liquid can be diverted 

from the measuring chamber of the device or the discharge line therefrom, except that a manually controlled outlet 

that may be opened for purging or draining the measuring system shall be permitted. Effective means shall be 

provided to prevent the passage of liquid through any such outlet during normal operation of the device and to 

indicate clearly and unmistakably when the valve controls are so set as to permit passage of liquid through such 

outlet. 

S.3.2. Discharge Hose. - The discharge hose of a measuring system shall be of the completely draining dry-hose 

type. 

S.4. Marking Requirements.

S.4.1. Limitation of Use. - If a measuring system is intended to measure accurately only liquids having particular 

properties, or to measure accurately only under specific installation or operating conditions, or to measure accurately 

only when used in conjunction with specific accessory equipment, these limitations shall be clearly and permanently 

marked on the device. 

S.4.2. Discharge Rates. - A meter shall be marked to show its designed maximum and minimum discharge rates. 

S.4.3. Temperature or Density Compensation. - Devices equipped with an automatic temperature or density 

compensator, shall be clearly and conspicuously marked on the primary indicating elements, recording elements, and 

recorded representations to show that the quantity delivered has been adjusted to the conditions specified in S.2.4. 

N. Notes 

N.1. Test Liquid. - A meter shall be tested with the liquid to be commercially measured except that, in a type evaluation 

examination, nitrogen may be used. 

N.2. Vaporization and Volume Change. - Care shall be exercised to reduce to a minimum vaporization and volume 

changes. When testing by weight, the weigh tank and transfer systems shall be pre-cooled to liquid temperature prior to 

the start of the test to avoid the venting of vapor from the vessel being weighed. 

N.3. Test Drafts.

N.3.1. Gravimetric Test. - Weight test drafts shall be equal to at least the amount delivered by the device in 

2 minutes at its maximum discharge rate, and shall in no case be less than 907 kg (2000 lb). 

N.3.2. Transfer Standard Test. - When comparing a meter with a calibrated transfer standard, the test draft shall be 

equal to at least the amount delivered by the device in 2 minutes at its maximum discharge rate, and shall in no case 

be less than 180 L (50 gal) or equivalent thereof. When testing uncompensated volumetric meters in a continuous 

recycle mode, appropriate corrections shall be applied if product conditions are abnormally affected by this test 

mode. 

(Amended 1976) 

N.4. Density. - Temperature and pressure of the metered test liquid shall be measured during the test for the 

determination of density or volume correction factors when applicable. For Liquid Density and Volume Correction 

Factors (with respect to temperature and pressure) the publications shown in Table N.4. shall apply: 

(Amended 1986 and 2004) 

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3.34. Cryogenic Liquid-Measuring Devices Handbook 44 - 2007 

Table N.4. Density or Volume Correction Factors 

Cryogenic Liquid Publication 

Argon 

Tegeler, Ch., Span, R., Wagner, W. “A New Equation of State for Argon Covering the 

Fluid Region for Temperatures from the Melting Line to 700 K at Pressures up to 

1000 Mpa.” J. Phys. Chem. Ref. Data, 28(3):779-850, 1999. 

Ethylene 

Smukala, J., Span, R., Wagner, W. “New Equation of State for Ethylene Covering the 

Fluid Region for Temperatures from the Melting Line to 450 k at Pressures up to 

300 Mpa.” J. Phys. Chem. Ref. Data, 29(5):1053-1122, 2000. 

Nitrogen 

Span, R., Lemmon, E.W., Jacobsen, R.T, Wagner, W., and Yokozeki, A. "A 

Reference Thermodynamic Property Formulation for Nitrogen." J. Phys. Chem. Ref. 

Data, Volume 29, Number 6, pp. 1361-1433, 2000. 

Oxygen Schmidt, R., Wagner, W. “A New Form of the Equation of State for Pure Substances 

and its Application to Oxygen.” Fluid Phase Equilib., 19:175-200, 1985 

Hydrogen 

"Thermophysical Properties of Fluids. 1. “Argon, Ethylene, Parahydrogen, Nitrogen, 

Nitrogen Trifluoride, and Oxygen,” published in the Journal of Physical and Chemical 

Reference Data, Volume 11, 1982, Supplement No. 1, and published by the American 

Chemical Society and the American Institute of Physics for the National Institute of 

Standards and Technology. 

Note: A complete database program containing all of the most recent equations for calculating density for various 

cryogenic liquids is available at www.nist.gov/srd/nist23.htm. There is a fee for download of this database. 

(Added 2004) 

N.5. Testing Procedures.

N.5.1. Normal Tests. - The "normal" tests of a device shall be made over a range of discharge rates that may be 

anticipated under the conditions of installation. 

N.5.1.1. 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, such as, 

temperature pressure and flow rate are reduced to the extent that they will not affect the results obtained. 

(Added 2001) 

N.5.2. Special Tests. - Any test except as set forth in N.5.1. shall be considered a "special" test. Tests shall be 

conducted, if possible, to evaluate any special elements or accessories attached to or associated with the device. 

A device shall be tested at a minimum discharge rate of: 

(a) 50 % of the maximum discharge rate developed under the conditions of installation, or the minimum 

discharge rate marked on the device, whichever is less, or 

(b) the lowest discharge rate practicable under conditions of installation. 

Special tests may be conducted to develop any characteristics of the device that are not normally anticipated under 

the conditions of installation. 

N.6. Temperature Correction. - Corrections shall be made for any changes in volume resulting from the differences in 

liquid temperature between time of passage through the meter and time of volumetric determination of test draft. 

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Handbook 44 - 2007 3.34. Cryogenic Liquid-Measuring Devices 

N.7. Automatic Temperature or Density Compensation. - When a device is equipped with an automatic temperature 

or density compensator, the compensator shall be tested by comparing the quantity indicated or recorded by the device 

(with the compensator connected and operating) with the actual delivered quantity corrected to the normal boiling point of 

the cryogenic product being measured or to the normal temperature and pressure as applicable. 

T. Tolerances 

T.1. Application.

T.1.1. To Underregistration and to Overregistration. - The tolerances hereinafter prescribed shall be applied to 

errors of underregistration and errors of overregistration. 

T.2. Tolerance Values. The maintenance and acceptance tolerances for normal and special tests shall be as shown in 

Table T.2. 

(Amended 2003) 

Table T.2. Accuracy Classes and Tolerances for Cryogenic Liquid-Measuring Devices 

Accuracy 

Class Application Acceptance Tolerance 

Maintenance 

Tolerance 

Special Test 

Tolerance 

2.5 Cryogenic products; liquefied compressed gases 

other than liquid carbon dioxide 1.5 % 2.5 % 2.5 % 

(Added 2003) 

T.3. On Tests Using Transfer Standards. - 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. 

(Added 1976) 

T.4. 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. See also N.5.1.1. 

(Added 2001) 

UR. User Requirements 

UR.1. Installation Requirements.

UR.1.1. Discharge Rate. - A device shall be so installed that the actual maximum discharge rate will not exceed the 

rated maximum discharge rate. If necessary, means for flow regulation shall be incorporated in the installation. 

UR.1.2. Length of Discharge Hose. - The discharge hose shall be of such a length and design as to keep 

vaporization of the liquid to a minimum. 

UR.1.3. Maintenance of Liquid State. - A device shall be so installed and operated that the product being measured 

shall remain in the liquid state during passage through the meter. 

UR.2. Use Requirements.

UR.2.1. 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.2.2. Condition of Discharge System. - The discharge system, up to the measuring element, shall be precooled 

to liquid temperatures before a "zero" condition is established prior to the start of a commercial delivery. 

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UR.2.3. Vapor Return Line. - A vapor return line shall not be used during a metered delivery. 

(Amended 1976) 

UR.2.4. Drainage of Discharge Line. - On a dry-hose system, upon completion of a delivery, the vendor shall leave 

the discharge line connected to the receiving container with the valve adjacent to the meter in the closed position and 

the valve at the discharge line outlet in the open position for a period of at least 

(a) 1 minute for small delivery devices, and 

(b) 3 minutes for large delivery devices, 

to allow vaporization of some product in the discharge line to force the remainder of the product in the line to flow 

into the receiving container. 

(Amended 1976) 

UR.2.5. Conversion Factors. - Established conversion values (see references in Table N.4.) shall be used whenever 

metered liquids are to be billed in terms of: 

(a) kilograms or pounds based on a meter indication of liters, gallons, cubic meters of gas, or cubic feet of gas; 

or, 

(b) cubic meters or cubic feet of gas based on a meter indication of liters or gallons, kilograms, or pounds; or, 

(c) liters or gallons based on a meter indication of kilograms or pounds, cubic meters of gas or cubic feet of gas. 

All sales of cryogenics shall be based on either kilograms or pounds, liters or gallons of liquid at NBP1

, cubic meters 

of gas or cubic feet of gas at NTP1

. 

(Amended 1986) 

UR.2.6. Temperature or Density Compensation.

UR.2.6.1. Use of Automatic Temperature or Density Compensators. - If a device is equipped with an 

automatic temperature or density compensator, this shall be connected, operable, and in use at all times. Such 

automatic temperature or density compensator may not be removed, nor may a compensated device be replaced 

with an uncompensated device, without the written approval of the weights and measures authority having 

jurisdiction over the device. 

UR.2.6.2. Tickets or Invoices. - Any written invoice or printed ticket based on a reading of a device that is 

equipped with an automatic temperature or density compensator shall have shown thereon that the quantity 

delivered has been adjusted to the quantity at the NBP of the specific cryogenic product or the equivalent volume 

of gas at NTP. 

UR.2.6.3. Printed Ticket. - Any printed ticket issued by a device of the computing type on which there is 

printed the total computed price, the total quantity of the delivery, or the price per unit, shall also show the other 

two values (either printed or in clear hand script). 

UR.2.6.4. 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.2.7. Pressure of Tanks with Volumetric Metering Systems without Temperature Compensation. - When 

the saturation pressure of the product in the vendor's tank exceeds 240 kPa (35 psia), a correction shall be applied to 

the written invoice or printed ticket using the appropriate tables as listed in Table N.4.; or the saturation pressure 

shall be reduced to 207 kPa (30 psia) (if this can be safely accomplished) prior to making a delivery. 

(Added 1976) 

 

1

 See Appendix D, Definitions. 

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