Dynamic Measuring System for Liquids (Other than Water)

Part IV of the Eighth Schedule of the Legal Metrology (General) Rules, 20101

Part 1: Terminology

Meter

An instrument intended for measuring continuously, memorize and display the volume of liquid passing through the measurement transducer at metering conditions.
Transducer is a device that converts mechanical signals to electronic signals for the calculator.

Measuring System

The meter with all ancillary and additional devices will constitute a measuring system.

Ancillary Devices

  • Zero-setting Device
  • Volume Indicating Device
  • Printing Device
  • Memory Device
  • Price Indicating Device
  • Totalizer
  • Correction Device
  • Conversion device
  • pre-setting device
  • self-service device

Conversion device means a device which converts a volume into a mass.

Metrological Characteristics

Absolute Error

The result of a measurement minus the true value of the measurand
(a quantity that is being determined by measurement).
Eabs = Vd − Vt where Eabs = Absolute Error,
Vd = Value Displayed and Vt = True Value.

Relative Error

The absolute error divided by true value of the measurand.
Erel = Eabs / Vt

Absolute and Relative Error

A fuel dispenser shows delivery of 10 l while a consumer gets 9.5 l.
Absolute Error is 10.00 - 9.50 = 0.50 l
Relative Error is (10.00 - 9.50)/9.50 = 0.05
Relative Error in % = 0.05*100% = 5%

In this chapter the percentage of relative error will only be considered.

Maximum Permissible Error

The extreme values permitted by the specification for an error.

Minimum Measured Quantity

The smallest volume of liquid for which the measurement is metrologically acceptable for that system.

Minimum specified volume deviation

The absolute value of the maximum permissible error for the minimum measured quantity of a measuring system.

Intrinsic error

The error of a measuring system used under reference condition.

Part 2: General

Field of Application [1(2)]
Liquids to be measured

  • Petroleum and related products diesel, crude oil, lubricants, LPG etc.
  • Liquid food - milk, cream, alcoholic and non-alcoholic beverages, soft drinks, vegetable oils etc.
  • Alcohol
  • Chemical Products like Acids, ammonia-solutions etc.
  • All other liquids excepts drinking cold water and hot water but including distilled water and de-ionized water.
Field of Operation [2(3)]

Characteristics required to be known for verification of a measuring system.

  • minimum measured quantity
  • minimum flow rate Qmin and maximum flow rate Qmax
  • minimum pressure Pmin and maximum pressure Pmax of the liquid
  • dynamic viscosity of the liquid
  • minimum temperature Tmin and maximum temperature Tmax of the liquid
  • environmental class.

Environmental Class

Measuring systems are divided into three classes according to climatic and mechanical environmental conditions:

  • class B for fixed instruments installed in a building,
  • class C for fixed instruments installed outdoors,
  • class I for mobile instruments, in particular measuring systems on trucks.
This information is required for severity test to be done during model approval. However, the OIML has withdrawn the classification.

Accuracy Classes [2(4)]

Classification of the measuring devices under this heading is based on their field of application, and not on the degree of accuracy.

Class Field of Application
0.3
  • Measuring Systems on Pipeline
0.5
  • Fuel dispensers for motor vehicles (Except LPG dispensers)
  • Measuring Systems on Road Tankers for liquids of low viscosity (≤ 20mPa.s) like milk (3) Alcohol, Isopropyle (2.4))
  • Measuring system for unloading of ship/ rail/ road tankers
  • Measuring system for milk
  • Measuring system for loading ships
  • Measuring system for refueling aircraft.
1.0
  • Measuring system (except LPG) for liquified gases at temperature ≥ - 10´C·
  • LPG dispensers for motor vehicles.
1.5
  • Measuring system for liquified carbon dioxide.

Maximum Permissible Error [2(5)]

Maximum Permissible Relative Error (±) for volumes two litres and above
Apparently, the use of term 'relative' was a mistake. Table 3 does not bear the term. The OIML omitted the term in 2007 edition.

Table 2

  Accuracy Classes
0.3 0.5 1.0 1.5
Line A
0.3 % 0.5 % 1.0 % 1.5 %
Line B
0.2 % 0.3 % 0.6 % 1.0 %

Line A: applicable to whole measuring system
Line B: applicable to metering unit for type approval

Maximum Permissible Error (±) for volumes below two litres

Table 3

Measured Quantity
Maximum Permissible Error
  • from 1 to 2 l
  • value fixed in Table 2, applied to 2 l.
  • from 0.4 to 1 l
  • twice the value fixed in Table 2
  • 0.2 to 0.4 l
  • twice the value fixed in Table 2, applied to 0.4 l
  • from 0.1 to 0.2 l
  • 4 times the value fixed in table 2
  • less than 0.1 l
  • 4 times the value fixed in table 2, applied to 0.1 l

* In the above table, the quantities 1 l and 0.4 l have been mentioned in two rows which is confusing as same value is derived from both the column.
* The OIML has used the term (applied to Minimum Measured Quantity, MMQ for Emin calculation) for clarification in 2007 edition.

Calculating Maximum Permissible Error

The MPE of a complete measuring system will be the greater of following two values:

Calculating Emin and MPE

Case I: When the minimum measured quantity of the dispenser is 2 litres or more

Emin = 2Vmin X A / 100
[A is the numerical value of line A in Table 2]
A diesel dispenser has a minimum acceptable volume capacity of 5 litres, say. Then
Emin = 2 x 5000 x 0.5 / 100 = 50 ml.
This dispenser delivers, say, 50 litres of diesel to a vehicle. Then,
Absolute MPE = 50 x 1000 x 0.5/100 = 250 ml
MPE is 250 ml.

Case II: When the minimum measured quantity is less than 2 litres

E min = 2 x value given in Table 3
and related to Line A of Table 2
A dispenser has a minimum acceptable volume of 0.5 litre and it delivers 1 litre fuel to a scooter.
Emin = 2 x 2(000) x 0.5 x 0.5/100 = 10 ml [for 1 l, the MPE scales is twice the value fixed in Table 2]
Absolute MPE, from Table 3 is 2 x 1000 x 0.5/100 = 10 ml.
MPE is 10 ml.

Applicability of of Maximum Permissible Error

Rule 2(6)

Maximum permissible errors in line A of Table 2 apply to complete measuring systems, under rated operating conditions, without any adjustment between the various tests, for:

  • type approval,
  • initial verification,
  • subsequent verifications.

Important!

When verifying a dispenser at user level, the whole measuring system will be checked for accuracy which should be within MPE
MPE = Class / 100.
For calculating MPE for 0.5 class instruments.
Convert the volume into mililitre and multiply by 5/1000.

EXAMPLE:
Volume Dispensed: 15 litre = 15,000 ml.
MPE = 15000 X 5 / 1000 = 75 ml.

Statutory Markings

Rule 2(19)

Each measuring system shall bear, placed together legibly and indelibly on the dial of the indicating device or on a data plate, the following information:

General

  • pattern (model) approval sign
  • manufacturer's mark
  • designation of the system
  • serial number and year of manufacture
  • class, if other than 0.5

Characteristics

  • minimum measured quantity Vmin
  • minimum flow rate Qmin and maximum flow rate Qmax
  • minimum pressure Pmin and maximum pressure Pmax of the liquid
  • dynamic viscosity of the liquid
  • minimum temperature Tmin and maximum temperature Tmax of the liquid
  • environmental class.

Sealing and Stamping

Rule 2(20)

Normally, lead seals will be used which should be easily accessible.

Electronic Sealing

When access to parameters that participate in the determination of results of measurement is not protected by mechanical sealing, the electronic sealing may be used.

Stamping

The stamping should be made on a permanently fixed Stamping Plate to be provided. Alternatively, it may be made on the Marking Plate.