Regarding passive contacts in the I/O table

As I understand it, those with separate power supply are called passive signals, while those with the power supply integrated with the signal are active signals.

I did a quick search on Baidu: An active contact is one whose one end is connected to an external power source; when the contact closes, it sends a high-level signal to the system. A passive contact, on the other hand, does not require an external power source – the system monitors whether the contact is open or closed in order to determine whether there is an input signal. In other words, “active means there is an output power source; the signal is supplied internally, while passive means there is no output power source – the signal is supplied from outside.” Active components generate electricity; it’s not just about a power supply – induction, electromagnetic induction, arcs, and so on can all produce electricity. Therefore, even when no circuit is connected, as long as the contact is in such an environment, it is likely to generate induced electricity or circuit electricity, and such contacts are considered active contacts. Under conditions of the same voltage and phase polarity, they behave very differently compared to circuits with different voltages and phase polarities. For example, in old-style AC contactors (CJ1), there is a pair of auxiliary normally open and normally closed contacts. When one of these pairs is connected to a high-voltage control circuit, the other pair connected to a low-voltage circuit may encounter problems, as it’s not possible to isolate arcs. Even if that pair isn’t connected to anything, it still remains an active contact relative to the low-voltage circuit. If both pairs are connected to the same voltage level and the same circuit, then the unused pair is passive. This problem is common in control circuits with voltages of 380V, 220V, and 24V. Another example is in environments with flammable gases – even if the contacts are isolated, insufficient insulation can lead to discharge, forming a circuit with the ground. Even in such cases, the contacts aren’t passive. Passive contacts serve to isolate and transmit control signals between different control circuits. The requirements regarding insulation, protection levels, etc., vary depending on the application; naturally, higher standards are better, and this also depends on the operating environment. In modern relays, within their safe insulation voltage range, most of the unused contacts are passive. However, caution is needed when dealing with pairs of normally open and normally closed contacts. 2. Here’s an example: (1) All frequency converters have digital output interfaces, one of which uses transistors for output – these are what we call active contacts ； (2) Inverters all have digital output; another type is output through switch contacts, which we refer to as passive contacts ； 3. Active contacts, such as transistor outputs; without a power supply, the transistor cannot function and thus this digital switch cannot operate ； 4. Passive contacts, such as those used in switch outputs, function merely to connect or disconnect external circuits; the power supply of these circuits does not affect the closing or opening of such contacts ；

I also searched on Baidu. . . Then all kinds of confusion{:3_69:}

Active and passive are relative terms; in the context of control system cards, if the field device requires power from the card, then it is a passive signal; if the field device has its own power supply, then it is an active signal. For example, three-wire and four-wire instruments are generally active signals. Another point is that if the equipment on-site requires power from a safety barrier, then it represents an active signal in terms of the card module, but a passive signal for the safety barrier; whereas if the card module provides the power directly, it is a passive signal.

An active signal is one in which the signal source itself can generate a signal; it does not require a power supply and can directly drive resistive loads. For example, in four-wire instruments, two wires are used for power supply and two wires for signals, with no additional power supply allowed in the signal circuit. }; It is a passive signal, and the signal circuit requires a power supply; otherwise, the signal source will not output any signal. For example, in two-wire transmitters, a power supply must be connected to the signal circuit. Contact and wet contact: These terms are used in reference to digital switches. Dry contact is a standard term in the field of industrial control. The dry contacts of a relay mean that the power supply for the contact circuit is provided by an external circuit; the relay merely acts as a \"node (contact)\\" to connect the circuit, without being involved in anything else” ； Wet contacts, on the other hand, correspond to dry contacts: in addition to providing contacts for closing the circuit, they also supply the current required in that circuit

The site requires active connections inside the power supply room, while passive connections are sufficient inside the area where power is not needed. For example, four-wire instruments require a separate power supply of 24V or 220V; the indoor signal wires are passive in such cases. Whereas for two-wire instruments, since the signal wires also serve as power lines, an active power supply is needed

The site requires active connections inside the power supply room, while passive connections are sufficient inside the area where power is not needed. For example, four-wire instruments require a separate power supply of 24V or 220V; the indoor signal wires are passive in such cases. Whereas for two-wire instruments, since the signal wires also serve as power lines, an active power supply is needed

Active and passive refers to signal processing: if the signal processing unit requires a power supply, it is passive; if the source of the signal has its own power supply, it is active.

Those that do not require power from a card are active, while those that do require it are passive