hotline tachometer sensor basic structure
Published on:2015-1-5 15:26:03 Hits:

1. Hotline probe

Hotline simple model shown in Figure 3-42 shows the probe. Thin wire placed perpendicular to the flow direction, fixed at both ends of the stent in the relatively thick metal wire by the current heated above the temperature of the measured medium.


Figure 3-42 hotline model

In order to meet the requirements of the probe on the use of the hotline, hoping hotline material has:

① temperature coefficient of resistance of materials high in order to obtain high measurement sensitivity;

② material must be corrosion resistant to ensure that there is sufficient stability;

③ material should have high mechanical strength to prevent deformation vibration affect the measurement accuracy;

④ timber division has good thermal conductivity.

Often, people can meet the above requirements using tungsten, platinum or platinum-plated tungsten wire to produce hot-wire probe on the hotline.

Typical hot diameter 0.5-10 m, a length of 1-3mm. The size of the major areas to consider: improving the sensitivity of the hotline, the hope hotline finer diameter, length is longer as well, but it will make the mechanical strength and reduced spatial resolution; improving the spatial resolution, the hope hotline the shorter the better, but it may affect the measurement sensitivity.

Welded to the ends of the hotline two prongs of the fork, the other end of the wire welded forks, plus a protective cover, fill in between the forks and the protective cover insulation. Forks usually made of stainless steel by 0.2-0.5mm diameter promoter, top diameter is 0.05-0.1mm. Forks embedded among ceramic, nylon or other insulating material, wrapped probe housing.

2. Hot-film probe

In order to apply the thermal velocimetry to measure liquid flow rate, the development of the hot-film probes. Its high mechanical strength, they are able to adapt to certain conditions, the more severe the flow field (such as sewage flow field flow, etc.). In addition, it is less affected by vibration, heat resistance can be adjusted by the film thickness, it is easier to match with the amplifier, a higher signal to noise ratio. Its disadvantage is the measurement frequency range is narrow, complex production process, lower operating temperatures, which are limiting its application.

Hot-film deep needle comprises thermal film, substrate, insulating layer and conductor sections. Sputtering a platinum film is heat formed on a substrate, a thickness of about 0.1-1 m. The substrate is made of quartz or borosilicate glass cylinder. In order to make the film with a fluid heat insulation and to prevent contamination of the outer membrane is coated with hot thickness of about 1 m around the quartz insulating layer.

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