BEKA BA377E, Manual

Page: 6 / 62

6
The BA377E EC-Type Examination Certificate
specifies that the equivalent capacitance and
inductance of the BA377E sensor input is:
Ci = 2nF
Li = 4µH
To determine the maximum permissible cable
parameters these figures should be subtracted from
the maximum permitted output parameters Lo and
Co specified by the certificate for the sensor
connected to the BA377E input terminals. The
BA377E input parameters are small and therefore
unlikely to make a significant difference to the
allowable cable parameters.
2.5.2 Sensors that require energising
Switch contacts, proximity detectors and open
collector sensors require energising which is
achieved by linking two BA377E terminals together
as described in section 2.5. When energised, the
output parameters of the BA377E input are:
Uo = 10.5V dc
Io = 9.2mA dc
Po = 24mW
These parameters do not comply with the
requirements for
simple apparatus and should be
considered when assessing the safety of the sensor
connected to a BA377E input.
Any certified intrinsically safe sensor may be
connected to the BA377E energised input providing
that the sensor's input safety parameters are equal
to, or greater than, the output safety parameters of
the BA377E input shown above. This is not
restrictive and most intrinsically safe sensors will
comply. A sensor complying with the requirements
for
simple apparatus , such as a mechanically
operated switch contact, may also be connected.
This allows most mechanically operated switches,
open collector transistors and certified intrinsically
safe NAMUR proximity detectors to be directly
connected to the BA377E energised input. The
sensor and wiring should be able to withstand a
500V rms insulation test to earth and the sensor
should be located in the same hazardous area as the
BA377E.
The maximum capacitance and inductance that may
be safely connected to the energised input (link
connected) is:
Co = 2.4µF
Lo = 200mH
Again this is not restrictive as the combined
capacitance and inductance of most sensors and
connecting cable will be less than this.
2.6 Remote reset terminals
Connecting the external reset terminals RS1 and
RS2 together will reset the BA377E when configured
as a Timer and synchronise the displayed time when
configured as a Clock. The two reset terminals have
the following input and output safety parameters:
Uo = 3.8V dc
Io = 1.6mA dc
Po = 2.0mW
Ui = 28V dc
Ii = 200mA dc
Pi = 0.84W
The equivalent capacitance and inductance between
them is:
Ci = 0nF
Li = 0µH
The maximum cable capacitance and inductance
that may be safely connected between the reset
terminals RS1 and RS2 is:
Co = 40µF
Lo = 1H
The reset terminals may be directly connected to any
mechanically operated switch located within the
same hazardous area as the BA377E. The switch
and associated wiring should be able to withstand a
500V insulation test to earth.
If the reset switch is required in the safe area a
Zener barrier or intrinsically safe relay is required to
transfer the contact closure into the hazardous area.
Almost any intrinsically safe relay with certification
permitting the contacts to be connected to equipment
in the hazardous area may be used. A positive diode
return Zener barrier may also be used as shown in
Fig 1.
When used as a Timer the BA377E may also be
reset from the display mode by operating the
&
and
*
push buttons simultaneously for more than two
seconds. See 6.5.19