Application of Rotary Paddle Switch in Level Measurement for Moisturized Materials

Fig.1 Material accumulation and scarring

So, is it true that rotary paddle switch cannot be used in level measurement for material that is moisturized or containing moisture? The answer is certainly “No”, not absolutely true. The characteristics of the measured material have a great impact on the service life of the instrument. What we could do is to find out how to avoid adverse effects. After going through a large number of tests and analysis, engineers in Jiwei found following measures could facilitate the applications of rotary paddle switch in level measurement for moisturized material.

Compared with horizontal installation, inclined installation can reduce material accumulation on the base of spindle during material filling process, reduce the amount of moisture to enter into the instrument and avoid overfilling due to false detection or “scar” phenomenon.

2. Install a V-shaped baffle

Rotary paddle switch is a contact level switch. The basic requirement for its installation is to avoid installing the probe on the way of material filling. In order to avoid the agglomerate material direct impact on the blade, it is necessary to install a V-shaped protective baffle above the rotary paddle switch. Due to inadequate consideration, no V-shaped baffle was installed on silos at the beginning. Unlike the shaft which was protected by a protective sleeve, the blade was not rigid enough to bear the impact from moisturized and easily agglomerated materials (such as sludge etc.). The blade was deformed almost 90 °due to the impact.

In addition, when the V-shaped protective baffle is installed, one must consider whether the space between protective baffle and spindle is too narrow or small because material containing moisture usually has poor fluidity and is easy to agglomerate. It is easy to accumulate in a narrow space (dead zone) and form “scars” on the shaft.

Because silo and level measurement instrument are two independent devices, protecting the measuring instrument usually is not in the consideration when selecting a silo. It undoubtedly increases the risk of being damaged for the rotary paddle switch. In addition to installing a baffle, using a silo with an alcove can also effectively avoid the risk. Let´s take a real application as an example to make a further explanation.