Level measurement

125 Instrument selection within the measuring principle

Fixation of rope probes • The fixation of the probe end may be required if otherwise the probe contacts the silo wall, the cone, the baffles/struts or other parts at times or if the probe converges closer than 0.5m/19.7" to a concrete wall. The probe weight provides an internal thread for this purpose:

• Please use preferably the 6mm/0.23" rope probe because of its higher tensile-loaded capacity when fixing a rope probe • The point of fixation must either be reliably grounded or reliably insulated. If a fixation with reliable grounding is not possible, the insulated lug offered as an accessory may be used • The rope must be loose to avoid extremely high tensile loads and the risk of breakage. Adjust the rope to a length which exceeds the required measuring range so that the rope slackens in the 1cm (0.4")/m rope length!

– 4mm/0.16" rope: M 14 – 6mm/0.23" rope: M 20

Slackening of the rope:

Reliably grounded point of fixation:

Reliably insulated point of fixation:

probe length

C

Tensile load • Bulk solids exert tensile forces on rope probes. Their intensity increases with: – The length of the probe or max. cover

• The tensile force values contain a safety factor of 2 (compensation of the fluctuation range in freely flowing bulk solids) • Since the tensile forces largely depend on the flow properties of the product, a higher safety factor is required for sluggishly flowing products and if a risk of product accumulation on walls exists. Use rather a 6mm/0.23" rope than 4mm/0.16" in critical cases • The same forces also act on the ceiling of silos. The tensile forces are larger on fixed ropes, but they cannot be calculated. Please observe the tensile-loaded capacity of the probes or ensure that this capacity is not exceeded • If the max. tensile load is exceeded, please verify whether a non-contact ultrasonic or level radar instrument should be used for the application

– The density of the product – The diameter of the silo and – The diameter of the probe rope

• The diagrams in the Technical Information TI01004F show typical loads in frequently occurring bulk solids as reference values. The calculations take the following conditions into account: – Freely suspended probe (end of probe not fixed) – Freely flowing bulk solids (mass flow). The core flow cannot be calculated. In case of collapsing product accumulation on walls higher loads may occur