BEKA BA377E, Manual

Page: 14 / 62

14
3.2.9 Control outputs - optional
Each of the two factory fitted optional control outputs
is a galvanically isolated single pole solid state
switch as shown in Fig 7. The outputs are polarised
and current will only flow in one direction. Terminals
A1 and A3 should be connected to the positive side
of the supply.
Ron = less than 5

+ 0.7V
Roff = greater than 1M

Note: Because of the series protection diode some
test meters may not detect a closed alarm
output
Fig 7 Equivalent circuit of each control output
Each control output is a separate galvanically
isolated intrinsically safe circuit with output safety
parameters complying with the requirements for
simple apparatus . This allows the control output
terminals A1 & A2 and A3 & A4 to be connected to
almost any certified intrinsically safe circuit protected
by a galvanic isolator providing the isolator has the
correct function and the output parameters do not
exceed:
Uo ≤ 28V
Io ≤ 200mA
Po ≤ 0.84W
The maximum equivalent capacitance and
inductance between each set of alarm terminals is:
Ci = 22nF
Li = 8µH (Effectively 0)
To determine the maximum permissible cable
parameters Ci and Li, plus those for any other
intrinsically safe instruments in the loop, should be
subtracted from the maximum permitted external
capacitance Co and inductance Lo specified by the
certificate for the galvanic isolator powering the
circuit as shown in Fig 8.
Fig 8 Typical control output application