Q1 How can I verify an USM ?

  •  All meters for Custody Transfer (CT) use, are calibrated in the factory on water. Depending on the viscosity range (>10 cSt) an additional calibration is carried out on a hydrocarbon product.
  • It is possible to verify liquid USM’s in the field by use of mechanical proving devises, such as Uni or Bi-Directional provers or Small Volume Provers. Proving, liquid USM’s, with these mechanical proving devises requires more runs or a larger proving volume than when using conventional meter such as a PD or Turbine meter. API has implemented a table in which the relation between repeatability and uncertainty is expressed. This implies that under the API recommendations it is allowed to initiate, as an example, 10 proving runs with a repeatability of 0.12% to achieve an uncertainty of 0.027%. API Chapter 4.8, Appendix A
  • There are also a number of different Master Meter configurations that can be used in the system layout, this concept is used for large flow rates where liquid USM’s of above 12” are required. It is not practical to use mechanical proving devises to above 2000 m3/hr.
Proving Runs Repeatability Limit Meter Factor Uncertainty
3 0,02 0,00027
4 0,03 0,00027
5 0,05 0,00027
6 0,06 0,00027
7 0,08 0,00027
8 0,09 0,00027
9 0,10 0,00027
10 0,12 0,00027
11 0,13 0,00027
12 0,14 0,00027
13 0,15 0,00027
14 0,16 0,00027
15 0,17 0,00027
16 0,18 0,00027
17 0,19 0,00027
18 0,20 0,00027
19 0,21 0,00027
20 0,22 0,00027

Q2 How do I verify an A-V with a SVP?

The A-V can be verified with a SVP according to the industrial standard for liquid flow meters. In general, independent of manufacturer, an USM requires more runs than a turbine meter. However the same table as explained in Q1 is applicable.

Q3 What are the main differences between OIML and API?

  OIML R-117 API
Instruments Recommendations dedicated to measuring systems per application i.e. gas or liquid (flowmeters in general) Standards dedicated to a specific flowmeter (Different API standards for liquid UFM, gas UFM, turbines, mass meters etc), in which recommendations are defined for the mnost optimum use of a certain measurement principle
Tests Guideline based on laboratory & field tests Standard based only on field trials
Proving CT instruments periodical laboratory proving CT duty instruments (PD, turbines, Coriolis & UFM) on site proving only (compact & full size provers, master metering) (*)
Approval document An approval can be initiated by an official governmental body for a specific type of flowmeter and manufacturer. API does not initiate any approval document, this implies that no flowmeter is supported by an API approval document.

Q4 What are the basic OIML R-117 requirements?

Turndown 10:1 +/- 0,15% +/- 0,15% +/- 0,20% +/- 0,15%
Turndown 20:1   +/- 0,25%    
Repeatability band 0,04% 0,04% 0,12% 0,07%

Q5 How can an USM being calibrated over a viscosity range of e.g. 200cSt?

Based on the primary process conditions i.e. flowrate, flowmeter diameter and viscosity, a minimum and maximum Reynolds number can be calculated for the specific application. After the Reynold’s range is calculated the appropriate HC products and calibration flowrates will be selected in such a way that the operational Reynold’s range is covered.

Q6 Why is a calibration on water sufficient to cover a viscosity range up to 10cSt?

As explained in Q5 the operational Reynold’s range is calculated. If this range fit’s within the Reynold’s range of the water calibration no HC calibration is required. Reynold’s numbers can be modified by changing the flow velocity. An example is calculated for an 12“ flow meter as specified in the table:

Reynold’s No. Water 1 cSt HC 5 cSt HC 10 cSt
25.000 0.1 m/s 0.5 m/s 1.0 m/s
50.000 0.2 m/s 1.0 m/s 2.0 m/s
250.000 1.0 m/s 5.0 m/s 10 .0 m/s
1.000.000 4.0 m/s    

Q7 Is KROHNE prepared for MID (Measuring Instrument Directive)?

• On 30 October 2006, the Measuring Instruments Directive (MID) came into force. As of that moment some things are changed for Krohne as manufacturer of measuring instruments and/or automatic weighing instruments. Good news: thanks to the harmonization through MID, one approval will enable you to sell your product in all the EU and EFTA countries. This means you need only one approval, which will be valid in 30 European countries. It may be clear that the MID has been introduced to diminish the trade barriers and to simplify the approval process.


• The MID for the A-V is under preparation and is expected to be available in 9/2008. For the time being the A-III will use already granted approvals.


• All national approvals obtained in the EU remains valid until 2016, after this date MID will be mandatory.

Q8 Is a flow conditioner always required?

•Krohne always recommends that a dedicated flow straightener be used. We have carried out significant R+D testing and computer modeling and as result our inlet spool pipe consists of a 10D flanged pipe section with a 4D ISO tube bundle inserted into the pipe section. This configuration is described and approved in all ALTOSONIC V CT approvals.


The actual metering section should be purchased with the meter and should be tested and calibrated fitted to the meter inlet flange. A system of sleeved bolt holes is used to ensure that the upstream section is fitted to the meter in the field in the same position as when it was tested. Other flow conditioners can be used providing the full installation details are sent in with the meter enquiry.

Q9 What are the minimum required upstream conditions?

Manufacturer USM model number of chords required upstream length with flow conditioner
Daniel Model 3804 4 13D
FMC Ultra 6 6 Not specified
Caldon LEFM 280 C 8 10D or 5D
Caldon LEFM 240 C 4 10D
Faure Herman FH 8500 18 10D

Q10 How do I link my USM to a flow computer?

In most CT applications the meter provides an actual volume pulse/frequency output to a flow computer which also receives inputs from a pressure and temperature transmitter so that the volume can be corrected to standard conditions according to international standards like API 2540.


The Altosonic V is been supplied with a UFP –V which is a flow processor which can provide a net volumetric measurement value given a pressure and temperature input. The UFP only provides flow computer functionality when used with the A-V, it cannot be used with any other metering devise unlike all other “flow computers”. The ALTOSONIC III output provides a double actual volume pulse output and does not have an integrated flowcomputer, consequently a dedicated flowcomputer is required to calculate nett volume.

Q11 Is accuracy related to the number of chords?


The more chords are available the more information is provided on the flow profile. While the flow profile is a direct parameter for the Reynold’s number the ALTOSONIC V, with 5 chords, is product independent. The ALTOSONIC III is equipped with 3 chords and therefore re-calibrations are required when product changes occur. For both flow meters the repeatability and accuracy are the same. More chords do decrease the effect of flow profile disturbances caused by turbulence profiles in the pipeline. The A-V integrated cone design decreases installation effects.

Q12 What percentages of water and gas can be accommodated in the fluid being measured?

It’s difficult to give a definitive statement as there are a number of factors that affect the actual concentrations. Depending on the CT application there may be other instruments to determine the actual flowing stream components i.e. BS+W monitors or dedicated sampling systems. If a customer is buying product then they don’t want to pay for water or gas. The liquid USM can carry on measuring with reasonable concentrations of water of gas but it cannot quantify the three phases.


If as an example a turbine meter is used on a CT application in which gas/air is present, the turbine meter cannot identify this content and consequently will measure gas/air as liquid volume. This immediately will introduce a significant error in the measurement, the ALTOSONIC V and III will immediately raise an alarm if gas/air is present giving the operator the possibility to adjust his process to avoid gas/air.

Q13 What is the viscosity range of the two types of Altosonic meters?


The Altosonic V has the widest range of viscosities for multi viscosity measurement. The OIML approval for this meter is up to 400 cSt. For high viscous applications >400 cSt please consult KROHNE, based on our long term experience we can supply High Viscosity flowmeters although each individual application need to be evaluated. The A-III can be used with viscosities up to 100 cSt providing that there is an in situ proving device available in the same way as a turbine meter is utilized for custody transfer applications.

Q14 How will I be notified in case an USM would fail?

The Altosonic V meter, when supplied with a panel mounted UFP, has a full diagnostics package including visual display of flow profile etc. Each individual path has live information concerning Signal to Noise Ration SNR and Velocity of Sound data. It is also possible to configure alarms to ensure that the meters performance is monitored continually. Integrated in the UFP we have the security checks on lost pulses and flow profile disturbances.

Q15 Are liquid ultrasonic meters affected by noise?

Due to the high frequency of the transducers used in liquid meters and the acoustic damping of the liquid, noise in the line does not affect the ability to determine the transit time difference between the upstream and down stream transducers.

Q16 How do I compare USM’s with other metering principles?

Metering principles Turn down ratio Max Flow rate [m3/h] Pressure drop Dedicated Strainer Sensitive to contamination Flow profile sensitivity High viscosity application Bi-directional measurement
P.D. Meter 10:1 2000 ++ Required high none + no
Multi bladed Turbine Meter 10:1 6000 + Required high Requires conditioner - no
Helical Bladed turbine meter 40:1 4500 + Required high Requires conditioner + no
Coriolis Meter 25:1 1000 + Not necessary medium none +++ Standard
Liquid Ultrasonic 40:1 8000 +++ Not necessary none Requires conditioner ++ Standard

Q17 Why do I select a KROHNE ALTOSONIC V over a A-III

You would select an Altosonic V if the customer wants to measure products over a wide viscosity range without having an in situ prover in use. This is due to the ability of an A-V to measure the volumetric flow rate independent of the flowing liquid properties such as Viscosity, Temperature, Density and the Velocity of Sound in the liquid. An ALTOSONIC III is calibrated on one product, in case this flowmeter is used on multi product applications it is mandatory to have a permanent installed proving device available on site.

Q18 You didn’t find your answer?

Please send your question to h.hofstede@krohne-oilandgas.com