In industrial automation and control systems, PLC (Programmable Logic Controller) is a commonly used device used to control various operations in machinery or manufacturing processes. Regarding the naming and classification of PLCs, there is no new term directly defined based on its physical installation location (such as a housing or cabinet). However, based on the description in the question, we can make a logical analogy and inference.
First, the question mentions "If all units are in one housing, then what PLC is called PLC?". The logic here is that under normal circumstances, regardless of whether the unit of the PLC is installed in a housing or other form of packaging, as long as it has the function of a programmable logic controller, it is called PLC. Therefore, the answer to this part is actually restating the basic definition of PLC, that is, regardless of its physical packaging form, as long as it meets the definition and function of PLC, it is called PLC.
Next, the question asks "If all units are in one cabinet, then plc is called _____ plc". Here, we are facing a description of the installation environment of PLC, rather than a new definition or classification of PLC itself. In industrial automation environments, PLCs and other related devices (such as input and output modules, power supplies, communication modules, etc.) are often installed in cabinets to protect these devices from environmental factors (such as dust, humidity, temperature fluctuations, etc.) and facilitate centralized management and maintenance.
However, from the perspective of PLC naming and classification, installing PLCs in cabinets does not constitute a new PLC category or subclass. PLCs are usually named based on their functions, manufacturers, processing power, input and output points, etc., rather than their physical installation environment. Therefore, even if all units are in a cabinet, it is still called a PLC without any specific prefix or suffix to indicate its installation environment.
In summary, if all units are in a cabinet, it is still called a PLC, not a specific type of "_____ plc". The blank here should be left blank or understood as a PLC in the conventional sense.