S-G-05—Specifications for In-situ Verification and Reverification of Flow Computers and Transmitters

S-G-05—Specifications for In-situ Verification and Reverification of Flow Computers and Transmitters (PDF, 44KB, 9 pages)

Information Bulletin: Specifications for In-situ Verification and Reverification of Flow Computers and Transmitters (S-G-05)

Category: GAS
Bulletin: S-G-05
Document(s): Refer to section 3 below
Issue Date: 2009-12-18
Effective Date: 2010-04-01
Supersedes:

Table of Contents

1.0 Scope

This specification applies to High Intervention Trade Transaction level metering sites where a flow computer has been installed.

This specification does not apply to Low Intervention Trade Transaction level metering sites granted conditional permission under Bulletin G-14 for using gas meters in service without verification and sealing.

2.0 Authority

These specifications are issued under the authority of sections 12(2) and 18 of the Electricity and Gas Inspection Regulations.

3.0 Normative References

3.1 Electricity and Gas Inspection Act (EGIA)

3.2 Electricity and Gas Inspection Regulations (EGIR)

3.3 LMB-EG-08, Specifications for Approval of Type of Gas Meters and Auxiliary Devices

3.4 PS-EG-02, Provisional Specifications for the Means and Methods of Sealing Verified Electricity and Gas Meters

3.5 G-14, Policy on Granting Conditional Permission for Using Gas Meters in Service without Verification and Sealing at the Low Intervention Trade Transaction Level of the Natural Gas Market

3.6 PS-G-14, Provisional Specifications and Procedures for the Verification of Correction Devices and Linearization Functions Incorporated in Meters and Flow Computers

4.0 Terminology

Calculator Function
Software coding installed in a flow computer that takes programmable fixed parameters and live inputs, from the connected devices, and calculates the corresponding multipliers and measurement units used in the billing transactions.
Connected Devices
Approved devices connected to a flow computer that measure one or more gas stream parameters such as temperature and pressure, and which provide input signals to the flow computer for use by its calculator function in the determination of the mass, volume and/or energy value used for billing transactions.
Flow Computer
A microprocessor based device that calculates and records volume consumption and/or time-stamped volume flowrates, expressed at line conditions and base conditions. It may optionally also calculate energy consumptions and energy flowrates. Calculations are performed by the calculator function. Examples of inputs include volume-weighted pulses and analogue or digital signals representing differential pressure, static line pressure, flowing gas temperature, gas composition, relative density and energy density (heating value). The device may be used with one or more associated gas meters of various types.
High Intervention Trade Transaction Level
This level of intervention includes all of the current intervention activities that Measurement Canada (MC) employs to regulate the natural gas trade sector. Metering devices in this level of intervention are subject to approval of type, initial verification, and subsequent reverification.
Low Intervention Trade Transaction Level
Trade transactions where the basis of the charge, for the gas supplied, is obtained from a meter falling within the scope of MC Bulletin G-14, for which conditional permission was granted under the subject requirements for use without verification and sealing.
Measuring Apparatus
A device required for inspection of gas meters, which has been certified by tracing its accuracy at one or more points to reference standards kept by the National Research Council of Canada and/or Measurement Canada.
Modular Approach
An inspection methodology whereby a connected device is tested using a measuring apparatus to determine the error of the device. The error in the transfer of the data from the device to the flow computer is considered a component of the device error.
Snapshot
A manually triggered electronic memorization of a flow computer's instantaneously registered values of volume pulse frequency, pressure, temperature, volume and energy flowrates, and other applicable measurement parameters and factors.
System Approach
An inspection methodology whereby the system is tested as a whole (i.e. the flow computer and its connected devices) to determine the overall system error.
Transmitter
Contains a transducer and may be equipped with telemetering capabilities. It converts one or more sensed inputs (such as gas temperature, static pressure, and differential pressure) to an analogue output signal (e.g. 4-20 mA, 1-5V, or resistance measurement) or a digital signal (which uses a particular communications protocol such as Hart, Mod Bus, or Field Bus, etc.).

5.0 General

5.1 This document provides the on-site inspection requirements for the flow computer and transmitters used in the determination of the measurement units used in billing for a particular gas metering installation site.

5.2 Where (re)verification of a connected device is based on the device indicator or measurement of the output, this document also provides the performance requirements to ensure that the data transfer is correct and the total of the device connection errors is maintained within the prescribed limits of error for the connected device.

5.3 Additional requirements specific to a particular connected device may be communicated through the Notice of Approval (NOA).

6.0 Metrological Requirements

6.1 Transmitters (including transducers)

6.1.1 Where a pressure or temperature transmitter or RTD does not hold a valid certificate, it shall be inspected.

6.1.2 The transmitter/RTD markings shall be as stated in the specifications for approval of type, plus any additional requirements identified in the NOA.

Table - 1
Transmitter/RTD Test Points and Tolerances
Temperature Transmitters and RTDs
Test Point Tolerance
0 ±1 °C

±2 °C

This tolerance is applicable to all output values over the approved operating range
Flowing gas temperature °C*
≥30 °C
*Where the flowing gas temperature meets the ≥30 °C criteria, a point approximately midway between zero and the flowing gas temperature shall used for this test point.
Static Pressure Transmitters
Test point (% of Line pressure) Tolerances (% of line pressure)
0%

± 1.0%

This tolerance is applicable to all output values over the approved operating range
50%
100%
 
Differential Pressure Transmitters
Test point (% of configured full scale) Tolerances (% of configured full scale)
0%

± 1.0%

This tolerance is applicable to all output values over the approved operating range
20%
40%
60%
80%
100%

6.1.3 A measuring apparatus shall be installed at the source of the transmitter/RTD to determine the error, at the applicable test points as outlined in Table 1.

6.1.4 The transmitter/RTD error shall be within the tolerances listed in Table 1 for the type of device, at all points within the device's approved operating range.

6.1.5 Transmitters shall be (re)verified using readings from one of the following sources, to determine the transmitter's calibration error relative to the measuring apparatus connected to that source:

  1. the uncorrected flow computer reading for the connected transmitter; or
  2. uncorrected (e.g. raw flow computer mA reading of the input) reading of the input signal and calculating the applicable reading; or
  3. the signal at the output of the transmitter and calculating the applicable reading; or
  4. the transmitter's indicator (e.g. display or handheld reader).

6.1.5.1

Where the output signal at the transmitter is used to determine the error it shall be measured with a measuring apparatus.

6.1.5.2

Where the output signal at the transmitter or the transmitter indicator is used to determine the error, the reading (or calculated reading) shall be compared to the uncorrected (non-linearized) flow computer reading (or calculated reading) for the process variable of the transmitter being evaluated, at a minimum of one of the test points for the transmitter. The error at the flow computer input shall not exceed the applicable transmitter tolerance in Table 1, and the difference shall not exceed 20% of the allowable tolerance for the transmitter.

6.1.6 An RTD shall be (re)verified using the flow computer readings for the RTD input to determine the error relative to the measuring apparatus installed at the source, and shall be within the tolerance in Table 1 for temperature transmitter/RTD.

6.2 Flow Computer

6.2.1 Markings

6.2.1.1

The flow computer's markings shall be as stated in MC's specifications for approval of type, plus any additional requirements identified in the NOA.

6.2.2 Software

6.2.2.1

The measurement modules/subroutines of the software used in the flow computer shall be confirmed as having been approved by MC, by means of identifying the software version.

6.2.2.2

All applicable programmable/configurable setup parameters used by the calculator function in the determination of the measurement units, shall be validated.

6.2.3 Flow Computer Inputs (modular approach)

All flow computer inputs that are used in the determination of measurement units shall be evaluated to ensure the flow computer receives the data being sent by the connected devices.

6.2.3.1 Pressure and Temperature Inputs

6.2.3.1.1

Where the transmitters/RTDs are also being (re)verified during the inspection, these inputs are evaluated during the “modular approach” inspection of the transmitter/RTD (see section 6.1).

6.2.3.1.2

Where the pressure and temperature input devices are not being (re)verified during the inspection, the flow computer inputs for these devices shall be evaluated at a minimum of one test point within the range of temperature or pressure anticipated for that metering site. The flow computer's uncorrected non-linearized reading, for the process variable of the transmitter/RTD being evaluated, shall not exceed the applicable tolerance listed in Table 1.

6.2.3.2 Gas Composition Input (modular approach)

6.2.3.2.1

Where the gas composition, heating value and any other quantity used to derive legal billing units, (i.e. mass density, specific gravity) are provided by an approved and verified on-site gas analyzer, these values shall be compared with the flow computer's registered values for the same sample of gas. The values reported by the flow computer shall be the same as those recorded on the gas analyzer report.

6.2.3.3 Meter Input(s) (modular approach)

6.2.3.3.1

Where the data received from the meter is in digital form, the flow computer's reading and the meter's output shall be the same, at the point in time when the flow computer's calculator function performs a calculation to update the readings on the flow computer.

6.2.3.3.2

Where the signal received from a meter is in the form of pulses or an analog signal, the flow computer's readings for pulse count, frequency, or interpreted analog signal, shall be within 0.2% of the source device. The combination of test duration and the resolution of the units used in the calculations shall be sufficient to ensure an error resolution of 0.05% (1 part in 2000).

6.2.4 Flow Computer Calculator Function

This section is not applicable to flow computers that only permit access for the programming of configuration parameters (i.e. the user cannot change the source coding).

6.2.4.1 Verification of Measurement Units used In Billing Transactions

6.2.4.1.1

Where there is access (e.g. initial inspection or seal not intact) to source coding of the measurement software modules/subroutines, the converted volume and/or energy accumulation calculations shall be verified over a combination of test points within the ranges of the connected devices (see 6.2.4.1.2 for methodologies and specific requirements). The calculation may be verified directly through accumulation tests or indirectly through snapshots of the frequency and volume and/or energy flowrates.

6.2.4.1.2

The tests in Table 2 shall be conducted to evaluate the overall converted volume/energy calculator function of the flow computer.

  1. The input values for the tests listed in Table 2 shall be fixed to maintain the necessary stability to evaluate the functioning of the calculator. The flowrate reading(s), for snapshots or test duration, and the units used in the accumulation tests, shall be sufficient to obtain a calculated error resolution of 0.1% (1 part in 1000).
  2. The test data obtained from (a), as indicated by the flow computer for the tests in Table 2, shall be within ± 0.2% of that calculated using an MC approved test program. Where applicable, linearization factors shall be applied to the MC approved test program results in accordance with PS-G-14.
Table - 2
Test No. Flowrate Temperature Flowing Pressure ΔP (orifice) Gas Composition
1 Mid range Mid range Mid range Mid range Mid range*
2 50% 15 ±5 °C 25% 40% Low HV*
3 50% 0 ±1 °C 100% 60% High HV*
4 90% 30 ±5 °C 50% 100% High HV*

* The gas composition values selected are based on the historical or expected range of heating values of the gas being metered at the metering installation site. Where the range of the heating value does not deviate by more than 5% from the historical or expected mean of the heating value, a single gas composition within the range may be used for all tests.

6.2.5 Flow Computer System Error

6.2.5.1

A volume/energy accumulation test, using the system approach, shall be completed at stable flowing conditions (see test 1 of Table 3 for test points). The test duration and resolution of test data shall be sufficient to obtain test results having a resolution of 0.1%.

6.2.5.2

Where the stability of the flowing gas pressure or temperature source does not provide the control necessary for this test, a separate source which is certified (or one that provides for monitoring the source with a measuring apparatus) shall be used to simulate flowing conditions.

6.2.5.3

A volume/energy accumulation test, using the system approach, shall also be completed for tests 2 and 3 of Table 3. These tests may be conducted using the snapshot method.

6.2.5.4

Where it is not possible or practical to obtain the pressure or temperature test points, a separate source which is certified (or one that provides for monitoring the source with a measuring apparatus) shall be used to simulate test conditions.

Table - 3
Test No. Flowrate Temperature Flowing Pressure ΔP (orifice) Gas Composition
1 ≥ 80% Flowing Temp. ±5 °C ≥ 80% Flowing Press. ≥ 80% Flowing Gas HV
2 ≥ 50% ≥ 25°C ≥ 50% ≤ 70% ≥ 50% Low HV
3 ≥ 50% 0 ±5 °C ≥70% ≤ 90% ≥ 50% High HV

6.2.5.5

The overall converted volume and/or energy accumulation or flowrates for snapshot method reported by the flow computer for each test shall be compared to the overall converted volume and/or energy calculated, using an MC approved test program. Where applicable, linearization factors shall be applied to the MC approved test program results, in accordance with the applicable section PS-G-14 for the programmed linearization method.

6.2.5.6 The total overall converted volume and/or energy error of a flow computer and its connected devices, shall not exceed ± 2.0% of the true values determined by the MC approved test program.

6.2.6 Flow Computer Outputs

6.2.6.1

The converted (corrected) volume output of a flow computer's pulse generator/initiator, if so equipped, is exempt from verification.

6.2.6.2

The unconverted (uncorrected) volume output of a flow computer's pulse generator/initiator, if so equipped and approved, shall be verified unless the pulse output has been permanently disabled.

6.2.6.2

The start/stop readings used for the test shall be those with the maximum resolution available in the flow computer. The duration of the test shall be sufficient to increment the flow computer register a minimum of two units, and shall result in a value that is representative of complete pulses. (e.g. a pulse weight of 1.2 units would require a duration sufficient to increment the flow computer register a minimum of five units)

6.2.6.3

The test volume represented by the output pulses shall match the corresponding volume registered by the flow computer.

7.0 Seals and Sealing

7.1 Unless otherwise permitted by the President of MC, pursuant to the EGIR, each meter verified for use in trade shall be sealed in accordance with MC Provisional Specification PS-EG-02: Provisional Specifications for the Means and Methods of Sealing Verified Electricity and Gas Meters.

7.2 Any additional sealing requirements stipulated in the applicable NOA shall also apply.

Alan E. Johnston
President
Measurement Canada