German term (edited): dig. (abbr.)

Digitale und analoge Eingangsmodule
=>
digital or analogue entry modules

Essential components for any PLC depending of the kind of connected measuring devices and drives, see below:

A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis. Dick Morley is considered as the father of PLC as he had invented the first PLC, the Modicon 084, for General Motors in 1968.
:
A PLC is an industrial microprocessor-based controller with programmable memory used to store program instructions and various functions.[18] It consists of:
• a processor unit (CPU) which interprets inputs, executes the control program stored in memory and sends output signals,
• a power supply unit which converts AC voltage to DC,
• a memory unit storing data from inputs and program to be executed by the processor,
• an input and output interface, where the controller receives and sends data from/to external devices,
• a communications interface to receive and transmit data on communication networks from/to remote PLCs.
https://en.m.wikipedia.org/wiki/Programmable_logic_controlle...

Note: During my professional activitiesas electrical engineer I learned to program and apply PLCs.

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Note added at 16 hrs (2021-09-27 10:00:00 GMT)
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Some of the most common digital and analogues I/O devices from Siemens (Simatic), Schneider (Modicon) and Allen-Bradley (Rockwell), I encountered in industrial environnements:

SIMATIC ET 200SP, digital input module, DI 8x 24 V DC High Speed, Pack quantity: 1 unit, three alternative operating modes: DI, Oversampling, 4x counters, suitable for BU type A0, Color code CC01
https://mall.industry.siemens.com/mall/en/WW/Catalog/Product...
:
SIMATIC ET 200SP, digital output module, DQ 4x 24VDC/2A Standard, suitable for BU type A0, Color code CC02, Module diagnostics
https://mall.industry.siemens.com/mall/en/WW/Catalog/Product...

SIMATIC ET 200SP, AI 4xI 2-/4-wire ST, Analogue input module, Analogue inputs: 4 (current 2/4-wire standard), 24 V DC, Module diagnostics, 16 bit, Colour code: CC03, Suitable for BU type A0 and A1
:
SIMATIC ET 200SP, AQ 4xU ST, Analogue output module, Analogue outputs: 4 (voltage/current standard), 24 V DC, Module diagnostics, 16 bit, Colour code: CC00, Suitable for BU type A0 and A1
https://www.automation24.biz/analogue-i-o-modules

Discrete input module, Modicon TM5, digital 4I,
100...240 V AC, 2 wires
https://www.se.com/ww/en/product/download-pdf/TM5SDI4A

Our Bulletin 1734 POINT I/O™ modules offer digital, analog, and specialty I/O, as well as POINT Guard safety-rated I/O, with one to eight points per module. You can mix standard and safety I/O in the same system.
https://www.rockwellautomation.com/en-us/products/hardware/a...

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Note added at 16 hrs (2021-09-27 10:03:12 GMT)
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Please read:
Digitale und analoge Eingangsmodule
=>
digital or analogue input modules

Sorry, I was tired yesterday late evening.