Discrete I/O (3I/3O) Connection; Active Inputs - Mettler Toledo IND500x Installationsanleitung

2.4.7 Discrete I/O (3I/3O) Connection

The IND500x provides three active inputs and three passive outputs as standard. Refer to [Main PCB Page 9]
for location of these inputs and outputs.
There are one 6-position terminal strip on the main board that provide connections to the inputs and one 6-
position terminal strip which provide connections to the outputs. These connections are described next.
See also
Main PCB Page 9

2.4.7.1 Active Inputs

Using the Discrete I/O option with active inputs enables connection of switches or other simple devices to trigger
an input. The terminal provides the intrinsically safe voltage internally making the input active and no voltage is
supplied by the external simple device.
Because the voltage supplied by the terminal for the active inputs is intrinsically safe, the external simple
device/switch does not need to be certified for use in intrinsically safe circuits located in hazardous gas
environments.
ATEX Guideline for Connection to Active Input: As simple equipment, according to the §5.7 EN/IEC 60079-11
the external simple device does not need to be certified for use in Intrinsically Safe circuits installed inside
hazardous gas environments. In hazardous dust applications, Table 1 of EN/IEC 61241-11 has to be taken
into account, e.g. for the certified Po = 2,94mW the relevant regulation applies and II2D approved input
devices should be used.
FM guideline for connection to the active input: Using simple apparatus as defined by section 504.2 of the
National Electric Code (NFPA 70) is "An electrical component or combination of components of simple
construction with well-defined electrical parameters that does not generate more than 1.5 volts, 100 milliamps,
and 25 milliwatts and is compatible with intrinsic safety of the circuit in which it is used." The Section 504.4
exception in the NEC states that "Simple apparatus, as described on the control drawing, shall not be required
to be listed."
An example of how to wire to the active inputs is shown in the following figure.
SWITCHES
Figure 22: Active Input Connections
IND500x
WARNING
Only the wiring connections are shown below and not all sealing or other
protective methods required for safe operations. All installations must be
correct per the local wiring code and must follow the entity approval concept.
SWITCHES SWITCHES
Installation​ ​ 25