29
OPTIMASS
3
CONNECTION OF SEPARATED SYSTEMS
3.1 General
In the case of separate systems, the sensor and converter are connected using 4 core 2 pair
cable with an overall shield. Each cable pair carries an intrinsically safe circuit (Power Supply
Circuit and Data Circuit). The maximum length of the connecting cable for functional reasons is
300m, provided that the capacitance and inductance of the cable does not exceed the limits
specified in section 3.2 below.
The requirements of IEC/EN 60079-14 should be adhered to when installing the flowmeter.
3.2 Cable Parameters
The following points need be to be followed when selecting the connect-
ing cable for separated systems:
• The maximum permitted total capacitance and inductance for the connecting cable is :
C
L
= 195 nF
L
L
= 310 μH
• Cable supplied by Krohne has the following parameters:
C
L
’
<
200pF/m
L
L
’
<
0.7μH/m
• The cable selected must have a temperature rating equal to or better than the maximum
range of temperatures present in the installation taking into account temperature gradients
on the flow sensors (see the notes in section 2).
• The cable must be capable of withstanding a test voltage of 1000V AC and have a minimum
insulation thickness of 0.2mm, as per IEC/EN60079-14 clause 12.2.2.7.
3.3 Equipotential bonding
The MFC 300F mass flow converter or OPTIMASS / OPTIGAS x300C mass flow meter must be
included in the equipotential bonding system of the installation using the equipotential bonding
terminal on the mass flow converter housing wall bracket or mass flow meter housing mount-
ing stem respectively.
In separated systems the intrinsically safe power supply and data circuits are galvanically iso-
lated from earth, therefore, an equilisation cable between the mass flow sensor and mass flow
converter should not be used.
Where screened cable is used, the screen should only be earthed at the mass flow sensor end.
In the special case of a screen being earthed at both ends of the system, a potential difference
between the sensor and converter is not permitted. Refer to IEC/EN 60079-14 clause 12.2.2.3
for further requirements for cable screens.
AD OPTIMASS 300_010 Haz Areas Rev 01.qxp 05/03/2014 13:25 Page 29
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