Measurement Protocol – Draft A

EURAMET project - Inter-comparison of 1000 L proving tank

This comparison will be guided by

Elsa Batista - IPQ

with the support of

Erik Smits - VSL

May 2010

1. Introduction

The aim of this project is to compare results and method calibration of a 1000 L proving tank. Both the gravimetric method and the volumetric method can be used. If the laboratory is capable to use both methods they can either choose one or do both and report both. This comparison will allow the participating laboratories to test the agreement of their results and uncertainties despite the different used equipment and different calibration method.

This comparison will also give a possibility in Euramet to have a comparison in the large volume capacity. So fare there has been only Euramet comparisons on the µL range, and smaller volumes like 100 mL, 5 L and 20 L.

2. Participants and time schedule

This comparison is expected to start in July 2010.

According to the schedule, every laboratory will have 3 weeks to complete the following activities: a) receive the TSs, b) make the measurements, c) send the TSs to the next participant.

3. Transfer standard

The proving tank that will be circulated is the property of VSL. It is made as follows (see Figure 1):

-carbon steel construction

-1000 L nominal volume at 20 °C

-double windows (glass plates) in the neck (front and back)

-scale extending from -1% to +1%, scale interval 0.01%, with a length of 225 mm

-approximate massexcluding the transport box: 300 kg

-diameter of main body: 1.35 m

-heightincluding the wheels: 2.60 m

-inner diameter of the neck: 330 mm

- coefficient of cubical thermal expansion of the TS: 0.0000335 °C-1

-RTD (Pt-100) including read-out calibrated by VSL, length: 300 mm

4. Test procedure

The participating laboratories should use their normal calibration procedure in order to obtain the volume at the graduation mark of 1000 L. Both gravimetric (weighing of water) and volumetric methods (filling from one proving tank to another) can be used.

The results must be given for a reference temperature of 20 ºC.

At the end of the main flow waite 30 seconds in order to let it drip.

Each laboratory has to describe the equipment used for the calibration and its traceability according to a spread sheet that will be supplied by the pilot laboratory.

When the standard arrive at the participating laboratory, a visual inspection should be made and the results be noted on the corresponding formats. IPQ, as the pilot laboratory for this comparison, should be informed about the arrival and departure dates and about the results of the visual inspection as soon as possible.

5. Transport and costs

For the transport the proving tank will be packed in a transportation box. VSL will provide this box. The actual transport should be done with a well-known company (for example TNT; DHL). Such companies are used to handle ATA Carnets, which is need since laboratories are outside the EU.

Each laboratory pays for the transport to the next laboratory. The material costs for the transportation box and the ATA carnet, will be divided between participating laboratories.

The circulation schedule will be drafted and agreed as soon as the list of participants is ready.

6. Results and uncertainty presentation

A spreadsheet will be supplied for the presentation of the results and the uncertainty budget according to the Guide to the Expression of Uncertainty in Measurement[1].

The laboratories are also asked to describe the uncertainty components in order that each laboratory results can be compared on a common basis.

The forms for the measurement results, data for ambient conditions and traceability of the reference standards should be filled in and returned to the pilot laboratory within one month after the measurements.

  1. Determination of the reference value

To determine the reference value the formula of the weighted mean will be used used, using the inverses of the squares of the associated standard uncertainty as the weights [2]:

(2)

To determine the standard deviation u(y) associated with y:

(3)

  1. References

[1] BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML; Guide to the expression of uncertainty in measurement (GUM), Geneva, 1995.

[2] M.G. Cox, The evaluation of key comparison data, Metrologia, 2002, Vol. 39, 589-595.

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