Eckhard Schleicher

Head Experimental technology
Senior Scientist, Building VEFK
Phone: +49 351 260 3230

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Conductivity and Temperature Needle Probes


For the investigation of multiphase flow with gaseous and liquid parts special needle shaped conductivity probes have been developed. These probes allow the measurement of local conductivity in the test volume (pipelines, reaction chamber) with a very high time resolution under extreme operating conditions (water/steam up to 300 °C temperature and 160 bar pressure). With the help of these probes it is possible to record averaged local gas fractions, flow velocities as well as bubble number and bubble sizes with a time resolution of 10 ksample/s. A special feature of the development is the combined conductivity and temperature needle probe. The probe tip, thereby, consists of a miniature sheath thermocouple, which allows the synchronous measurement of temperature and conductivity at the same measuring point in the medium. Needle probes and the appendant data acquisition electronics are manufactured for many years at Helmholtz-Zentrum Dresden-Rossendorf and are used in many research centres worldwide. The momentary main field of application are experimental basic research studies in safety relevant thermo hydraulic facilities of nuclear power plants. Such investigations are used for analysis of accident sceneries as well as for the evaluation and further enhancement of thermo hydraulic simulation codes as CFX for problems of multiphase flow media.

Measuring Set-Up and Functional Principle


combined conductivity and temperature needle probe
conductivity needle probe
The developed needle shaped conductivity probes have many different constructive embodiments. The principle assembly consists of a coaxial structure of three stainless steel electrodes. Around a stainless steel wire as a centre electrode two steel tubes are arranged steplike. The single electrodes are isolated from each other by the use of a non conductive layer (mostly ceramics). To the central measuring electrode a bipolar voltage is applied. Depending on the resistance of the surrounding medium there is a current flow to the outer reference electrode. The middle electrode eliminates the interference of thin liquid films between the measuring and the reference electrodes in case of a gas bubble at the probe tip. The reference electrode serves as the outer cover of the needle probe fitting into the special test facility. It carries the outer forces and realizes the mounting of the electrical connector.
probe tip of a conductivity needle probe

A new quality in needle probe measurements has been carried out by the development of the combined thermo needle probe. Thereby, a sheath thermocouple replaces the stainless steel wire as the centre electrode. The jacked pipe of the thermocouple serves a measuring electrode for the conductivity measurement and the electrical isolated thermocouple measures the temperature.

In the last years a huge number of needle probe types have been developed and manufactured with again and again improved technologies. In the meantime a number of standard probes are produced by one of our extern cooperation partners, the Feinmechanisches Fertigungszentrum Glashütte.

Data Acquisition

Former electronic variants, due to the low data transfer rate of the RS232-interface, were not able to transmit the raw data sampled with 10 ksample/s. Only time averaged values and the number of phase changes were transmitted to the data acquisition computer, which caused a pre-processing of the acquired data. Thereby, the maximum and minimum conductivity values are derived for a period of one second. Based on the maximum value a upper and lower threshold is defined. Crossing these boundaries indicates a phase change at the probe tip from a medium with higher to a medium with lower conductivity and the other way round.
In cooperation with teletronic Rossendorf GmbH a new electronic variant has been developed. The modular system consists of one pre-amplifier module for each probe which amplifies the conductivity and temperature signals and transmits these signals in a pulse length modulation scheme to the data acquisition module. Each data acquisition modules allows the connection of up to eight pre-amplifier modules, which can be acquired synchronous. The data acquisition module is connected to the measuring PC by 10 Mbit Ethernet line. The computer streams the received data directly to the hard disk. By the use of a fast modern personal computer up to three data acquisition modules can be connected to via a Ethernet switch. Thereby, a synchronous data acquisition of 18 temperature and conductivity channels with a data rate of 10 kHz is possible.

pre-amplifier module
data acquisition module

Data Evaluation and Visualization

The acquired raw data can be visualized and evaluated by the use of a special developed software tool. From the raw data massive parameters like local void fractions over different integration periods as well as bubble count and phase temperature are derived, visualized and exported in ASCII-format for further investigations. Firstly, the raw data are smoothed and maximum and minimum values, respectively gas and liquid levels, are determined. From these values threshold levels can be derived to binaries the measuring signal into liquid and gaseous phase. Good threshold values are 35 % and 65 % of the signal range between maximum and minimum value. The local void fraction can be calculated as the ratio of the summarized time periods with gaseous phase and the total measurement time. A global threshold level and the definition of a minimal difference between gas and liquid level allow a save decision of the aggregate state in case of one phase flow periods.
visualization and data evaluation software
The flash-animation beside simulates the acquisition of the local conductivity in a bubble column by use of a conductivity needle probe for user defined bubble numbers. Afterwards the acquired data can be analyzed to calculate local void fractions. The animation takes approximately one minute and has a size of 15 kbyte.
(flash-animation 15 kbyte)


  • Baldauf, D.; Prasser, H.-M.; Zschau, J.
    Anordnung zur Messung der lokalen elektrischen Leitfähigkeit und Temperatur in Fluiden
  • Prasser, H.-M.; Zschau, J.; Böttger, A.
    Anordnung zur Messung der elektrischen Leitfähigkeit mittels Sonden sowie zur Sonden-Funktionskontrolle
  • Prasser, H.-M.; Zschau, J.; Böttger, A.
    Anordnung zur Messung der lokalen elektrischen Leitfähigkeit in Fluiden
  • Prasser, H.-M.; Böttger, A.; Schütz, P.; Zschau, J.; Fleischer, S.; Gocht, T.; Hampel, R.
    Füllstandswächter zur diversitären Grenzwertmeldung an Siedewasserreaktoren - Entwicklung und Erprobung
    Vortrag und Beitrag zu Sammelwerken (Proc., etc.): Jahrestagung Kerntechnik 2002, Stuttgart, 14.-16. Mai 2002.
  • Li, W.; Hicken, Enno F.; David, Paul H.; Prasser, H.-M.; Baldauf, D.; Zschau, J.
    Messung der Kondensatfilmdicken in einem dampfdurchströmten horizontalen Rohr
    Vortrag und Beitrag zu Sammelwerken (Proc., etc.): Jahrestagung Kerntechnik 2001, Dresden, 15./17. Mai 2001, Tagungsbericht S. 103-106.
  • Baldauf, D.; Prasser, H.-M.; Tamme, G.; Zippe, W.
    Nadelsonde zur Messung der Leitfähigkeit in Flüssigkeiten oder Mehrphasengemischen
  • Schäfer, F.; Krepper, E.
    Rechnungen zum 1%-Leck an der Versuchsanlage PMK-2 mit dem Code ATHLET
    Vortrag und Beitrag zu Sammelwerken (Proc., etc.): Proc. Jahrestagung Kerntechnik, Nürnberg, 16. - 18. Mai 1995, S. 79 - 82
  • Prasser, H.-M.; Böttger, A.; Schaffrath, A.
    Strömungsformen bei Kondensationsvorgängen im Notkondensator-Versuchsstand
    Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-186 Juli 1997
  • Böttger, A.; Gocht, T.; Prasser, H.-M.; Zschau, J.
    Transiente Kondensationsversuche an einem Notkondensator - Einzelrohr
    Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-383, Juli 2003
  • Weber, P.; Kusch, S.; Prasser, H.-M.
    Analysis of two-Phase Flow Phenomena with Conductivity Probes in Integral Reactor Safety Experiments
    Contribution to foreign collected edition (Proceeding ...): European Two-Phase Flow Group Meeting, Piacenca, Italy, June 6 - 8, 1994,
    Other report: Erlangen: Siemens AG, Power Generation Group (KWU), Paper I.1, 1994
  • Prasser, H.-M.; Küppers, L.; Mai, M.
    Conductivity Probes for Two-Phase Flow Pattern Determination During Emergency Core Cooling (EEC) Injection Experiments at the COCO Facility (PHDR)
    Contribution to foreign collected edition (Proceeding ...): Held on: OECD (NEA) CSNI SPECIALIST MEETING ON INSTRUMENTATION TO MANAGE SERVERE ACCIDENTS GRS, Cologne, Germany, 16th - 17th March 1992, Proceedings of the 1. OECD (NEA) CSNI-Specialist Meeting o ...
  • Aszodi, A.; Krepper, E.; Prasser, H.-M.
    Experimental and numerical investigation of one and two phase natural convection in storage tanks
    Heat and Mass Transfer 36 (2000) 6, 497-504
  • Gaschenko, M. P.; Prasser, H.-M.; Zippe, W.; et. al.
    Experimental Investigation of Accidental Thermohydraulic Processes under Circuit Depressurization at ISB-VVER Safety Integral Test Facility
    Contribution to foreign collected edition (Proceeding ...): International Symposium on Two-Phase Flow Modelling and Experimentation, Rom, Italy, October 09 - 11, 1995, p. 537
    Lecture (Conference): International Symposium on Two-Phase Flow Modelling and Experimentation, Rom, Italy, October 09 - 11, 1995
  • Maroti, L.; Prasser, H.-M.; Windberg, P.
    Investigation of two-phase flow phenomena at integral test facilities using needle conductivity probes
    Lecture (Conference): 8th International Conference on Thermal Engineering and Thermogrammetry, Budapest, 2.-4.6.93
    Contribution to foreign collected edition (Proceeding ...): 8th International Conference on Thermal Engineering and Thermogrammetry, Budapest, 2.-4.6.93, p. 275 - 280
  • Ezsöl, G.; Szabados, L.; Prasser, H.-M.
    Local void measurements in integral-type experiments simulating nuclear power plant transients
    Vortrag und Beitrag zu Sammelwerken (Proc., etc.): 5th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, Thessalonoki, Greece, 24-28 September 2001, Vol. 2, pp. 1637 - 1641.
  • Prasser, H.-M.; Böttger, A.; Zschau, J.; Gocht, T.
    Needle shaped conductivity probes with integrated micro-thermocouple and their application in rapid condensation experiments with non-condensable gases
    Kerntechnik 68 (2003) 3, pp. 114-120.
  • Szabados, L.; Ézsöl, Gy.; Perneczky, L.; Krepper, E.; Prasser, H.-M.; Schäfer, F.
    Two-phase flow behaviour during a medium size cold leg LOCA test on PMK-2 (IAEA - SPE-4)
    Helmholtz-Zentrum Dresden-Rossendorf; HZDR-101 August 1995
  • Prasser, H.-M.; Zippe, W.; Baldauf, D.; Szabados, L.; Ézsöl, Gy.; Baranyai, G.; Nagy, I.
    Two-phase flow behaviour during a medium size cold leg test on PMK-II (SPE-4)
    Lecture (Conference): Jahrestagung Kerntechnik 1994, Stuttgart, 17.-19.5.1994
    Contribution to foreign collected edition (Proceeding ...): Jahrestagung Kerntechnik 1994, 17.-19. Mai 1994, Stuttgart, Tagungsbericht, ISSN 0720-9207, S. 77-80
  • Kern, T.
    Void fraction measurement in foams using needle shaped conductivity probes
    Poster und Beitrag zu Sammelwerken (Proc., etc.): The Second European Congress on Chemical Engineering: "Chemical Engineering for competitiveness and employment in process industries", 5-7 October 1999, Montpellier, France, proceedings on CD-ROM, 09010004.pdf.
  • Prasser, H.-M.; Schlenkrich, C.
    Void Fraction Measurements in Transient Bubble Columns by Needle-Shaped Conductivity Probes
    ·Lecture (Conference): 33rd European Two Phase Flow Group Meeting, Hertogenbosch, The Nederlands, 30 May - 02 June 1995
    ·Contribution to foreign collected edition (Proceeding ...): 33rd European Two Phase Flow Group Meeting, Hertogenbosch, The Nederlands, 30 May - 02 June 1995, paper F2
  • Prasser, H.-M. (Editor) 
    4. Workshop "Measurement techniques for stationary and transient multiphase flows", Rossendorf, November 16 - 17, 2000
    Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf, HZDR-320 Mai 2001.