Power supply, potential groups

The terminals from the ELM3xxx series have different structures depending on their function.

The electronics of a fieldbus-connected I/O device generally consists of two potential groups (exceptions possible, see respective device documentation):

the communication section, the so-called bus side. This is usually supplied by the control voltage U_S.
In EtherCAT Terminals this section is directly connected to the internal 5 V supply from the E-bus and is not directly accessible by the user.
the signal section, for connecting the input/output signals, the so-called field side.
This is usually supplied by the peripheral voltage U_P. It consists of 1..n function channels.

usually all channels of the device are contiguous in this island, there is no electrical isolation (separate GND) of the channels.
in some devices, channels or channel groups may in turn be isolated as sub-islands. The height of the max. permissible electrical isolation is then specified. The device then consists of several potential groups: the bus side and the n channels.
depending on the device, the field side can also be supplied
- indirectly via U_S by transporting the necessary power via the electrical isolation from the bus side to the field side; connection of U_P (or power contacts) is then not required.
- directly via U_S
in special cases (e.g. EL6070 dongle terminal etc.) there is no accessible field side.

Both potential groups are usually electrically isolated. The "load capacity" of the isolation must then be observed in detail, i.e. the voltage difference/potential difference in continuous operation or for a short time between the two areas.

The internal electronics can be supplied via the bus side, field side or both, depending on the device. See the relevant notes about this in the respective device specification.

The plug used can also have an influence on the potential groups; if necessary, its housing is conductively connected to the housing of the terminal.

The external system GND (DIN rail, SGND, FE) is always present and represents the reference ground.

In the following the permissible potential difference is referred to only as "Insulation"; the exact specification (value, type and, if applicable, insulating strength) can be found in the respective specifications of the device.

Notice

Isolation between the potential groups in practice

The potential groups are theoretically electrically isolated, i.e. there are only parasitic ohmic connections in the range of MΩ and higher that are unavoidable due to the electronics.
The load capacity of the isolation with regard to voltage level and duration is specified. It results among other things from internal isolation distances and the group-spanning components used, e.g. data transmitters or transformers, and is formulated in view of the underlying standards, which describe application aspects such as aging, contamination or defined overvoltage events.
From this it can be seen that, in practice, potential groups cannot to be operated arbitrarily isolated from the environment. In particular, if EMC disturbances penetrate the potential group, conducted by the external cables or radiated, then this energy seeks its way to SGND and finds it in every case undefined in the group-spanning elements mentioned above. Therefore, practice has shown that potential groups of all kinds should be purposefully and intentionally connected to each other and to SGND with small capacitances in the nF range for interference dissipation, so that the HF interference (and this already starts at 50 Hz) finds a defined path and does not impair the operability.
The ohmic effect of the capacitors in relation to the parasitic ohmic effects is negligible.

The following potentials schematics may be specified for the ELM3xxx:

Power supply, potential groups 1: — Potentials schematics ELM300x-0000

Power supply, potential groups 2: — Potentials schematics ELM3002-0205

Power supply, potential groups 3: — Potentials schematics ELM310x-0000

Power supply, potential groups 4: — Potentials schematics ELM3102-0100

Power supply, potential groups 5: — Potentials schematics ELM3142-0000/ ELM3144-0000

Power supply, potential groups 6: — Potentials schematics ELM3146-0000

Power supply, potential groups 7: — Potentials schematics ELM3148-0000

Power supply, potential groups 8: — Potentials schematics ELM334x-0000

Power supply, potential groups 9: — Potentials schematics ELM334x-0003

Power supply, potential groups 10: — Potentials schematics ELM350x-0000

Power supply, potential groups 11: — Potentials schematics ELM360x-0000

Power supply, potential groups 12: — Potentials schematics ELM360x-0002

Power supply, potential groups 13: — Potentials schematics ELM370x-0000

Power supply, potential groups 14: — Potentials schematics ELM370x-0001

Power supply, potential groups 15: — Potentials schematics ELM3702-0101

Schematics for further terminals in preparation.