BEKA BA377E, Manual

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Fig 6 BA377E Timer used with galvanic isolators
with input sensor in safe area.
3.2.1 Power supply
The BA377E requires a minimum of 10V between
terminal 1 & 2 and consumes:
10mA without optional backlight
plus 22mA with optional backlight
plus 6mA when terminals 3 & 4 are linked
Any galvanic isolator certified for the gas group and
Zone in which the BA377E is installed may be used
to power the instrument. The output safety
parameters of the isolator must be equal to or less
than the input safety parameters of terminals 1 & 2
and the voltage at terminals 1 & 2 must be greater
than 10V. These requirements are not restrictive
and allow a wide range of galvanic isolators, such as
solenoid drivers, to be used.
3.2.2 Sensor inputs
As shown in Fig 5 the BA377E input can be directly
connected to hazardous area sensor, or to safe area
sensors via isolators as shown in Fig 6. Galvanic
isolators are not required in series with the inputs if
the intrinsically safe sensor is located within the
same hazardous area as the BA377E. The input
must be maintained, not momentary,
The BA377E may be used with a wide variety of
sensors, the following table shows the switching
thresholds for each type. For reliable operation the
input signal must fall below the lower threshold and
rise above the upper threshold.
Sensor
Switching thresholds
Lower Upper
Low voltage range 1.0V 3.0V
High voltage range 3.0V 10.0V
Proximity detector 1.2mA 2.1mA
Switch
100

1000

Open collector
2k

10k

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.
3.2.3 Switch contact input
Any mechanically activated switch contact may be
directly connected to input terminals 5 & 6 providing
the switch is located in the same hazardous area as
the BA377E, and the switch and associated wiring
can withstand a 500V rms insulation test to earth.
Most magnetically activated industrial push buttons
and reed relays comply with these requirements.
The BA377E contains a configurable debounce
circuit to prevent false triggering of the instrument.
Three levels of debounce protection are available.
See section 6.5.6
3.2.4 Open collector input
Any open collector sensor located in the same
hazardous area as the BA377E, such as a
mechanically activated opto-isolator, may be directly
connected to input terminals 5 & 6. The sensor and
the associated wiring must be able to withstand a
500V rms insulation test to earth.
The BA377E contains a configurable debounce
circuit to prevent false triggering. Three levels of
debounce protection are available See section 6.5.6