EGU2020-10360
https://doi.org/10.5194/egusphere-egu2020-10360
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Strain gauge measurements in hydraulic experiments: Chinese firecrackers versus industrial solutions

Martin Wolff and Ingo Schnauder
Martin Wolff and Ingo Schnauder
  • TU Vienna, Institute of Hydraulic Engineering and Water Resources Management, Research Unit Hydraulic Engineering, Austria (martin.wolff@tuwien.ac.at)

Force measurements using load cells equipped with strain gauges are widely applied in hydraulic experimentation and field surveys. In our case, drag on 5 horizontal cylinders in cross-flows had to be measured directly in a hydraulic water flume. We tested different setups and came up with a two-load cell solution per cylinder as mechanically best way to fix the cylinders in the flume.
The costs for an amplifier system of industrial standard is in the order of magnitude of 10.000 Euro and for load cells around 500 Euro. For our multiple cylinder application, the costs of an industrial standard solution exceeded the budget and forced us to find alternatives. Chinese-made load cells cost only a few Euros each. We designed our own measuring system, consisting of an external analogue-digital converter and a microcontroller. A Python script was programmed to operate the microcontroller and analyse the data.
In the session, we will give an overview of the flume setup and the measuring system – including live operation. We will discuss the required calibration procedure for the load cells and data quality and give recommendations for further improvements.

How to cite: Wolff, M. and Schnauder, I.: Strain gauge measurements in hydraulic experiments: Chinese firecrackers versus industrial solutions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10360, https://doi.org/10.5194/egusphere-egu2020-10360, 2020

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version 1 – uploaded on 28 Apr 2020
  • CC1: Comment on EGU2020-10360, Nils Rüther, 29 Apr 2020

    Thank you for the interessting slides. In your conclusion you said that, if one has the budget for the more professional equipment, this would be the prefered solution. I was wondering if this recommendation is based on experience and if so, what is the benefit of the professional equipement in terms of measurement accuracy. If not, maybe you could shortly comment on what you think is the difference in accuracy. Thank you very much. Nils Rüther

  • AC1: Comment on EGU2020-10360, Ingo Schnauder, 29 Apr 2020

    Hi Nils!

    Accuracy in loadcell measurements depends on many factors and is more tricky thanb anything else I've workd with in flumes until now.....Why?

    - System stiffness, the way you mount the cylinders/cells in the flume. We started with a swing-prototype, used a clamping mechanism and ended up with a relatively fixed and sadly less adjustable setup. Even the deformation of the flume at different water levels was an issue in some runs. It's tricky. Stiffness matters a lot.

    - We also tested two-cell and one-cell setups (in one cylinder), with the one-cell setup being more direct and making calibration easier.

    - The cell's force range itself...first you have to find the right load type, obviously. We expected forces up to only 30 N but we went for a 200 N load cell, which was again - stiffer to be built in. This meant, we lost some accuracy in the low discharge runs (say below 3 N). But this is not a problem of the quality standard of the cells.

    - About the absolute accuracy, we'll perform analyses of it and will know more soon. The calibration itself showed very accurate linearity of the signal of the cheap cells, which seems promising. We do not have directly comparable data of the drag runs in the flow, as we did not install the industrial standard cells submerged in water. All constructions with the cells outside of the water were not stiff enough (see point 1) :)

    cheers !

    ingo

     

  • AC2: Comment on EGU2020-10360, Ingo Schnauder, 29 Apr 2020

    Hi Nils!

    Accuracy in loadcell measurements depends on many factors and is more tricky thanb anything else I've workd with in flumes until now.....Why?

    - System stiffness, the way you mount the cylinders/cells in the flume. We started with a swing-prototype, used a clamping mechanism and ended up with a relatively fixed and sadly less adjustable setup. Even the deformation of the flume at different water levels was an issue in some runs. It's tricky. Stiffness matters a lot.

    - We also tested two-cell and one-cell setups (in one cylinder), with the one-cell setup being more direct and making calibration easier.

    - The cell's force range itself...first you have to find the right load type, obviously. We expected forces up to only 30 N but we went for a 200 N load cell, which was again - stiffer to be built in. This meant, we lost some accuracy in the low discharge runs (say below 3 N). But this is not a problem of the quality standard of the cells.

    - About the absolute accuracy, we'll perform analyses of it and will know more soon. The calibration itself showed very accurate linearity of the signal of the cheap cells, which seems promising. We do not have directly comparable data of the drag runs in the flow, as we did not install the industrial standard cells submerged in water. All constructions with the cells outside of the water were not stiff enough (see point 1) :)

    cheers !

    ingo