KROHNE BM 702 - Input Parameters and Measuring Ranges; Measured Quantity: Distance, Level, Volume, Reflection

BM 70 X Project Engineering Guidelines 01/2001 Page: 5
3 Input
3.1 Measured quantity (distance, level, volume, reflection)
The primary measured quantity is the distance between a reference point (as standard: tank mounting
flange) and a reflecting surface (e.g. surface of the liquid).
The filling level is determined by allowing arithmetically for the entered tank height.
Volume measurements are possible by entering a conversion table (max. 50 points).
The strength of the reflected signal can be measured for qualitative assessment of the tank product or
its surface (only BM 70 A/P).
3.2 Measuring range [0.5...20/35/40/100 m]
Minimum tank height: 0.5 m (1.64 ft)
The maximum measuring range is for:
BM 70 A 40 m (131 ft), optionally up to 100 m (328 ft)
BM 70 P 35 m (115 ft)
BM 702 20 m (65.6 ft)
Wave-Stick version 20 m (65.6 ft) recommended
The useful range depends on the antenna size, the reflection properties of the tank product,
the installation position, and the presence of interference reflectors (see Sections 6.1 and 7.3).
3.3 Block distance
The block distance is the minimum measured distance between the mounting
flange (reference point) and surface of the tank product.
Recommended minimum values: see sketches.
Horn antenna without still well:
Product surface
Stora
g
e tanks: 10cm/4"; Process tanks: 20cm/8"
Antenna size* = Type3: 22cm/8.7"; Type4: 34cm/13.4";
* Hastello
y
: -3cm/1.2"
Recommended Antenna distance:
Length of any antenna extension used must be added on!
Still well / Wave-Guide: Wave-Stick
Product
Antenna size * = Type1: 11cm/4.4";
Type2: 15cm/5.9"; Type3: 22cm/8.7"
Recommended antenna distance =
30 cm / 12" (BM 702: 50 cm / 20")
(Wave-Guide: no antenna)
* Hastelloy: -3cm (1.2")
Wave-Stick SW: 6cm/2.4"
384 mm/15.1"
Product
max.
200 mm
Standard:
8"
Minimum block distance =
Standard: 184 mm (7.24“)
General: Rod length - 200 mm (7.87“)
3.4 Behaviour when measuring range exceeded
In the event of the level measuring range being exceeded (including flooding) the measured value will
stick at the block distance, which is adjustable.
If the measured level value drops below the range, it will stick at the set lower range limit (distance =
tank height).
Maximum
level
Block
distance