BEKA BA368C, Manual

Page: 49 / 93

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3.4.1 Power supply
The BA368C galvanic isolator system certificate
lists a wide range of certified galvanic isolators that
may be used to power the instrument. If using the
entity concept to select an isolator, in addition to
matching the safety parameters, the isolator must
be capable of supplying 10V dc minimum at 20mA
to the BA368C.
3.4.2 Inputs
When the BA368C is programmed as a timer both
input A and input B are operational and may be
independently programmed to operate with almost
any pulse output transducer.
The following table shows the switching thresholds
for the various transducers. For reliable operation
the input signal must fall below the lower threshold
and rise above the upper threshold.
Input Switching
thresholds
Switch
100
Ω
1000
Ω
Proximity
detector
1.2mA 2.1mA
Open
collector
2k
Ω
10k
Ω
Magnetic
pick-off
0mV 20mV
peak
Voltage
pulse
1.0V 3.0V
The intrinsic safety requirements are explained in
section 1.4.3 Almost any mechanically or
magnetically activated switch, intrinsically safe
NAMUR 2-wire proximity detector or intrinsically
safe voltage may be directly connected to these
two inputs.
If the BA368C is located in a hazardous area but
the transducer(s) is in a safe area, a galvanic
isolator is required to transfer the transducer
output to the instrument. The system certificate
defines some galvanic isolators which may be
used.
3.4.3 Resetting the timer
When terminals 7 & 8 are connected together the
timer will be reset to zero if counting up, and to the
set time (‘SEt t’) if counting down. To achieve
reliable resetting the contacts must close for at
least one second.
Resetting may be accomplished by any
mechanically operated switch located in the
hazardous area providing it can withstand a 500V
rms insulation test to earth for one minute. No
galvanic isolator is required.
The BA368C timer may also be reset from within
the safe area. Any switch may be used but a
galvanic isolator is required to transfer the contact
closure into the hazardous area. The system
certificate lists some of devices that may be used.
Fig 3.2 illustrates how the timer may be reset from
both the safe and the hazardous areas.
3.4.4 Options
When the BA368C is calibrated as a timer, optional
control outputs may be used. The intrinsic safety
features of these are described in section 1.9.3.2
of this manual.