# What types of inputs can be connected to a PLC?

**URL:** <https://forumautomation.com/t/what-types-of-inputs-can-be-connected-to-a-plc/14567>\
**Category:** Siemens\
**Tags:** plc\
**Created:** [November 2, 2026, 12:55pm UTC](https://forumautomation.com/t/what-types-of-inputs-can-be-connected-to-a-plc/14567 "2026-11-02T12:55:07Z")\
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**Author:** ![Rabert](https://forumautomation.com/user_avatar/forumautomation.com/rabert/32/6784_2.png) [@Rabert](https://forumautomation.com/u/Rabert)\
**Post date:** [November 2, 2026, 12:55pm UTC](https://forumautomation.com/t/what-types-of-inputs-can-be-connected-to-a-plc/14567/1 "2026-11-02T12:55:08Z")

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# **What types of inputs can be connected to a PLC?**

A **[Programmable Logic Controller (PLC)](https://forumelectrical.com/how-to-test-plc-digital-inputs-and-outputs/)** receives process data through different input interfaces for monitoring, control, and industrial automation.

1. Digital Inputs (DI)

Receive discrete ON/OFF signals from push buttons, limit switches, proximity sensors, photoelectric sensors, and float switches.

2. Analog Inputs (AI)

Measure continuous signals such as 0–10 V, ±10 V, 4–20 mA, and 0–20 mA. RTDs and thermocouples require compatible input modules or signal transmitters.

3. High-Speed Inputs (HSC)

Capture high-frequency pulses from incremental encoders, pulse flow meters, and position feedback devices for counting and speed measurement.

4. Communication-Based Inputs

Receive process data through industrial communication protocols such as Modbus RTU/TCP, PROFINET, EtherNet/IP, EtherCAT, CANopen, and PROFIBUS.

5. Specialty Inputs

Use dedicated interfaces or compatible communication modules for load cells, RFID systems, barcode scanners, machine vision systems, energy meters, and servo feedback.

 ![1](https://cdn.forumautomation.com/original/2X/a/a3f702da6ed2cee795d41a765458cc8ba2edfcad.jpeg)

**Technical Note:** Input compatibility depends on the PLC model, module specifications, signal type, voltage/current range, resolution, isolation, and communication protocol.