What do dry contacts and wet contacts mean in instruments?

If a field instrument requires a DCS card to supply it with 24V power, then such an instrument is considered a passive signal for the DCS. Conversely, if the field instrument already receives 24V power from another source, it does not need power supplied by a DCS card, and in this case the instrument is considered an active signal. Active and passive signals require different wiring; for example, in HONEYWELL’s TPS, AI cards 1 and 2 are connected to passive signals, while cards 2 and 3 are connected to active signals, meaning no external power supply is needed. In the CS3000, jumper settings are required. )JO:EQ Dry contact: This refers to EX in the context of DO. If the coil power supply for the relay used by DO comes from the field instrument, it is called a dry contact. For example, some alarm lights | buzzers. The wiring also needs to change. -Definition of dry contact_r _7 Definition of dry contact: passive switch ； Has two states: closed and open ； There is no polarity between the two contacts, allowing them to be swapped ； Common dry contact signals include: 1. Various switches such as limit switches, travel switches, foot switches, rotary switches, temperature switches, level switches, etc ； 2. Various buttons ； 3. Outputs from various sensors, such as those used in environmental condition monitoring: water intrusion sensors, fire alarm sensors, glass breakage sensors, vibration sensors, smoke sensors, and condensation sensors ； 4. Outputs of relays and reed switches ； Where there are dry contacts, there are also wet contacts. The definition of a wet contact is: an active switch ； It has two states: powered and unpowered ； There is polarity between the two contacts; they cannot be connected in reverse ； Common wet contact signals include: 1. If the above dry contact signals are connected to a power supply, and the other terminal of the power supply is used as the output, then that constitutes a wet contact signal ； In industrial control, the common voltage range for wet contacts is DC0–30V, with DC24V being the more standard value ； The AC110～220V output can also be a wet contact, although this is less common ； 2. It’s also acceptable to use the TTL level output as a wet contact ； Under normal circumstances, TTL levels require buffered outputs, such as 7407, 245, 244, etc., which form a circuit with VCC and other components ； 244 and 245 can also form a circuit with gnd ； To drive the optocoupler at a distance. 3. Collector output of the NPN transistor and VCC ； 4. Collector output of the Darlington transistor and VCC ； 5. Outputs of infrared reflectance sensors and through-beam sensors ； In the field of industrial control, dry contacts are used far more often than wet contacts, thanks to the advantages associated with their lack of polarity: 1. They can be connected arbitrarily, which reduces engineering costs and the requirements for skilled personnel, thereby accelerating project completion. 2. It is possible to handle a large number of dry contact switches. 3. Even if the wires connecting the dry contacts become short-circuited over time, this will not damage either the local control equipment or the equipment located at a distance. 4. They are easy to connect, and their interfaces are easy to standardize. In other words, dry contacts are passive switches ； Has two states: closed and open ； There is no polarity between the two contacts, allowing them to be swapped ； Wet contact: active switch ； It has two states: powered and unpowered ； There is polarity between the two contacts, and they cannot be connected in reverse. Dry contacts are the opposite of wet contacts; a wet contact consists of a switch along with a power supply, and when it is closed, there is a certain voltage present, with no need for a detection circuit to supply current. When the dry contact is closed, there is no voltage; the current is supplied by the detection circuit. |(C What we refer to as dry contacts usually means passive contacts, that is, contacts that do not provide their own power supply; for such contacts, the power supply comes from an external source-

Both dry contacts and wet contacts are contact signals, that is, digital input signals (DI). In simple terms, a dry contact signal means that the digital input signal has no power supply ； A wet node means that the signal at that connection already has a power supply.

Difference between dry nodes and wet nodes. Definition of a dry node: a passive switch； Has two states: closed and open ； There is no polarity between the 2 nodes, so they can be swapped ； Common dry-contact signals include: 1. Various switches such as limit switches, travel switches, foot switches, rotary switches, temperature switches, level switches, etc ； 2. Various buttons ； 3. Outputs from various sensors, such as those used in environmental condition monitoring: water intrusion sensors, fire alarm sensors, glass breakage sensors, vibration sensors, smoke sensors, and condensation sensors ； 4. Outputs of relays and reed switches ； The definition of a wet node is: an active switch ； It has two states: powered and unpowered ； There is polarity between the two contacts; they cannot be connected in reverse ； Common wet node signals include: 1. If the above dry node signals are connected to a power supply, and the other terminal of the power supply is used as the output, then that constitutes a wet node signal ； In industrial control, the common voltage range for wet nodes is DC0 to 30V, with DC24V being the more standard value ； The AC110～220V output can also be a wet node, although this is done less frequently ； 2. It’s also acceptable to use the TTL level output as a wet node ； Under normal circumstances, TTL levels require buffered outputs, such as 7407, 245, 244, etc., which form a circuit with VCC and other components ； 244 and 245 can also form a circuit with GND ； To drive the optocoupler at a distance. 3. Collector output of the NPN transistor and VCC ； 4. Collector output of Darlington transistor and VCC ； 5. Outputs of infrared reflectance sensors and through-beam sensors

Well, field-effect switching transistors also have wet contacts.

I’ve learned it, thank you:victory: