BM 702
 

Frequency Modulated Continuous Wave(FMCW)-Radar uses a high-frequency signal (~10 GHz) which increases in frequency linearity during the measurement (frequeny sweep). The signal is emitted, reflected on the measuring surface and received time-delayed. For further signal processing the difference Δf is calculated from the actual transmit frequency and the receive frequency. The difference is directly proportional to the distance i.e. A large frequency difference correspond to a large distance and vice versa. This frequency difference is converted into a frequency spectrum using a Fourier transformation (FFT) and yields the distance to the surface. The level in turn is the difference between surface and previously determined empty tank distance.

Technical data
Operating mode/system structure FMCW radar in the X band (8.5-9.9 GHz) with digital signal processing;
compact device, modular design
Input
Measured quantities
Primary quantity
Derived quantities
Measuring range
Min. tank height
Max. measuring range
Block distance
Rate of change in level

distance
level, volume

0.5m(1.6ft)
20m(65.6ft)
min. 0.2 – 0.5 m (0.7 – 1.6 ft)
≤ 10 m/min (≤ 33 ft/min)
Output
2-wire connection










Failure signal
 
Type passive (current sink); EEx-ia
Current range  4 – 20 mA (error: 3.6/22 mA)
Accuracy/linearity 0.1 % (rel. 20 mA; 20°C/68°F)
Temperature drift ≤ 150 ppm/K (typically 50 ppm/K)
Power supply ≥ 17 V (I = 4 mA); ≥ 13 V (I = 20 mA) max. 30 V
Current output: error signal 3.6/22 mA, plain text in local display
Measuring accuracy
Error of measurement
Repeatability
Measured-value resolution
Ambient temperature effect
min. ±1 cm (0.4”) or ±0.2%
≤ 0.5 x error of measurement
1 mm (0.04'')
no temperature effect on measured value (see output)
Field service conditions
Installation conditions

Ambient conditions
Hazardous locations
Ambient temperature at signal converter
avoid interference reflections and multiple reflections

Zone 0, 1, 2; IIC/IIB, T1 –T6
–20 … +55°C (–4 … +131°F); functional range: –40 … +70°C (–40 … +158°F)
 
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