KROHNE BM 70 M - Manual (Page 14)

14 BM 70 M
5.3 Repeatability
Repeatability is equal to half the value for the error of measurement.
5.4 Measured value resolution/hysteresis
Measured value resolution is 0.1 mm / 0.004" for BM 70 M.
Hysteresis is at least 20 times less than the error of measurement.
5.5 Transient recovery time
The transient recovery time is determined by the setting parameter "time constant" (1 ... 100 s).
The transient recovery time relative to 1% deviation from the steady-state value is approx. 4.6
times the time constant.
However, in the case of unusually rapid changes in level, the transient recovery time may deviate
from this figure.
5.6 Long-term drift
The long-term drift is within the specified error of measurement.
5.7 Effect of ambient temperature
Temperature coefficient, signal output:
Ex-e current output HART
®
< 100 ppm/°C (typically: 30 ppm/°C)
Ex-i current output HART
®
< 100 ppm/°C (typically: 30 ppm/°C)
Current output < 200 ppm/°C (typically: 70 ppm/°C)
Digital interfaces no temperature effect
The temperature has no effect on the measured value as the device carries out a regular self-
calibration.
The temperature of the atmosphere above the liquid product results theoretically in -1 ppm/°C for
air.
When ascertaining temperature effects using reference measurements in liquid tanks, it needs to
be remembered that liquids generally have a high coefficient of expansion (organic liquids:
typically 0.15 %/°C)!
6 Operating conditions
Hazardous-duty systems:
• The BM 70 M is certified in conformity with European Standard (ATEX) for use in Zone 0, 1
and 2 hazardous locations.
• The BM 70 M also has FM Approval (Factory Mutual) for CLASS I, DIV 1, GROUPS B,C,D;
CLASS II/III, DIV 1, GROUPS E,F,G (in preparation)
•
Attention is drawn to the information given on the nameplate and the specifications in the
approval certificates.
• When carrying out installation, dismantling work or making electrical connections in the
hazardous area, be sure to observe the pertinent wiring and installation regulations, e.g. as
specified in VDE 0165.
•
Within the scope of routine checks required to be carried out on systems operated in
hazardous areas (maintaining the system in good working order), the "flameproof enclosure"
(large cover on signal converter) should also be visually inspected for signs of external
damage and corrosion.
• Before opening the "flameproof enclosure" (e.g. to inspect the inside or for repair purposes)
make absolutely certain in the hazardous location:
- that the BM 70 M Level-Radar is disconnected from voltage, and then allow the prescribed
waiting time of 22 minutes to elapse first,
- and that there is no explosion hazard (gas-free certificate!).