KROHNE BM 70 M - Manual (Page 92)

6 BM 70M-EEx/ BM 70Mi-EEx
Application restrictions:
• Flange system V96 with heating
The operator shall ensure that the temperature of the heating medium, when used in Zone 0,
shall not exceed 80% of the ignition temperature (in °C) of the product(s) in the tank, and
shall not exceed the maximum allowable flange temperature as a function of the temperature
class. The operating pressure of the heating system to be limited to max. 6 bar. Ensure that
the inlet and outlet of the heating system are correctly connected (see information plates on
the upper side of the flange).
•
Flange system V96 or SA with purging device and/or sensor connection
When delivered, the purge connection and sensor connection are each closed off by a G½“
or G¼ “ screw. Connection and operation of the purge and sensor connections fall within the
responsibility of the operator. When the screw plug for the purge and/or sensor connection is
removed, the operator is responsible for ensuring conformance with the “Ex” requirements
pertaining to the purge and/or sensor connection (e.g. fitting a flame trap).
The operator is also responsible for selecting a suitable purging medium.
3.3 Temperature classes, complete device
3.3.1 General
In respect of maximum surfaces temperatures, level measuring devices are exposed to three
heat sources:
•
Ambient temperature Tamb
• Electric power loss Pv
• Product temperature Tm
Accordingly, at a given maximum ambient temperature (Tamb < 60°C) and a given maximum
loss power, we obtain maximum surface temperatures as a factor of the product temperature.
For that reason, the devices are not allocated to any specific temperature class; rather, the
temperature class of the devices is a function of the actual product temperature.
3.3.2 BM 70 M-EEx with flange system V96 or SA
To simplify definition of the temperature class of the BM 70 M-EEx level gauges with flange
system V96 or SA, the only reference temperature required is the temperature at the device
flange of the level gauge. If the following maximum values are not exceeded at the device
flange, this will ensure that all other thermal limit values at the device are also maintained.
The temperature class can be defined in one of two ways:
• Without measurement of the flange temperature
If the flange temperature is not known, the product temperature shall be taken as being the
reference temperature for the flange.
• With measurement of the flange temperature
For operating conditions requiring Category 2 equipment, the product temperature may
assume higher values than the flange temperature, taking into consideration the limit values
of the temperature classes. The flange temperature should be established under “worst
case” conditions (e.g. allowing for the maximum possible product level and any additional
insulation measures).
For both systems – BM 70 M./V96 and BM 70 M./SA – the maximum product level to satisfy
safety requirements is the tank mounting flange.