F870S
2 Pressurized enclosure system F870S
Page 10
Gönnheimer Elektronic GmbH
Tel.: +49 (6321) 49919-0
Fax: +49 (6321) 49919-41
2.4.5 Continuous
flow
The control unit FS 850S incorporates the operation mode „continuous flow“. This operation
mode is necessary, for example if an analyzer produces an explosive atmosphere inside
the enclosure (containment system). The operation mode continuous flow flushes the en-
closure permanently. After the (pre-) purging procedure (purging process) a set-point flow
rate is adjusted during normal operation. A flow rate minimum will be monitored also.
This system design allows a
simultaneous PID- control
of cabinet pressure and flow rate
and opens new possibilities within the construction of pressurized enclosure systems and
applications.
In operation mode "continuous flow" the FS870S is capable to lower the flow rate from a
high value during purging to a low value during normal operation at a constant, low cabinet
pressure level. (Example: 3 liters/sec. to 0.3 liters/sec. decrease without pressure variation)
Figure 5: time diagram
2.4.6 F870S - Application using „Containment Systems “
„Containment Systems“ are defined as parts of a device within a pressurized enclosure,
which could emit combustible gas (or occasionally an explosive environment: zone 1, ex-
plosive mixture) from within the enclosure.
In order to receive an Ex p-System including a „Containment System“, which is failsafe ac-
cording EN 60079-2, with the attribute 'no emission', the following conditions must be met:
1. The flammable substance inside the containment system is in the gas or vapor phase
when operating between the specified temperature limits
2. The minimum pressure specified for pressurized enclosure is at least 50 Pa higher than
the maximum pressure specified for the containment system
3. An automatic safety device initiates, if the pressure difference falls below 50 Pa.
This automatic safety device can be activated by a difference pressure switch, looped into
the external alarm loop (terminal 5/6 on FS870S). If an alarm occurs on this loop, the con-
trol device FS870S will turn off the ignition-capable device immediately. After alarm cancel-
ing the control device FS870S starts operation automatically with the purging procedure.
The external alarm loop is made by a normaly closed connection method.
Summary of Contents for F870S
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