I would like to ask about the meaning of symbols in Siemens PLCs; please help
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Question: What do DC/DC/DC and AC/DC/DC mean in the CPU 226 CN DC/DC/DC, 24 inputs/16 outputs 6ES7 216-2AD23-0XB8, and the CPU 226 CN AC/DC/relay, 24 inputs/16 outputs 6ES7 216-2BD23-0XB8?
AC/DC/RLY——Power supply: AC 220V； Input: DC24V ； Output: Relay output DC/DC/DC — Power supply: DC24V ； Input: DC24V ； Output: DC24V
That one is a relay contact without power supply; it can be connected to both DC and AC power. The DC version probably comes with its own 24V supply
Relay outputs are generally used for solenoids and motor switches. The DC output for switching purposes is usually a regulated signal in the range of 4–20 MA: D
The relay outputs a dry-contact signal, which can generally be used directly to start small systems and as an intermediate relay. The DC output is from a transistor, and it carries the 24V voltage of the system’s power supply; therefore it cannot be connected directly to the control circuit, as this could cause a short circuit. A relay is needed to isolate it and convert the signal into a dry contact before it can be connected. However, it is generally not recommended to connect the output of a relay directly, mainly to prevent damage to the contacts caused by incorrect wiring or the impact of heavy loads on those contacts. It is better to use transistors with one gate per transistor, as they can be used more frequently. But if your signal is not used to drive large loads, a transistor can be chosen, which can reduce the number of connections significantly.