Siemens 6ES5464-8MF21 Analog Input Module

Core PT100 Temperature Measurement Function

The Siemens 6ES5464-8MF21 is a specialized analog input module for the SIMATIC S5 PLC family. This module interfaces directly with PT100 resistance temperature detectors (RTDs) for precise temperature measurement. It provides two independent input channels in a 4‑wire configuration for accurate, lead‑compensated readings. Consequently, it converts temperature changes into digital values for S5 CPUs without requiring external signal conditioning.

Precision 4‑Wire Measurement and Excitation

This module employs a constant‑current excitation source of approximately 2.5 mA for each RTD channel. It measures the resulting voltage drop across the sensor using Kelvin (4‑wire) sensing to eliminate lead resistance errors. The 6ES5464-8MF21 offers 12‑bit resolution and built‑in linearization to convert resistance to temperature internally. Furthermore, it features galvanic isolation between the measurement circuit and the S5 backplane for enhanced noise immunity.

Technical Specifications and Hardware Details

Engineers designed this module for the S5‑90U, S5‑95U, S5‑100U, ET 100U, and ET 200U systems. Its 20‑pin front connector provides clear terminal assignments for excitation and sense leads. The following table details its primary functional and electrical parameters.

Parameter	Specification
Manufacturer / Series	Siemens / SIMATIC S5
Product Model	6ES5464-8MF21
Module Type	Analog Input Module (RTD‑PT100)
Number of Channels	2
Sensor Type	PT100 (4‑wire configuration)
Excitation Current	≈ 2.5 mA constant current per channel
A/D Resolution	12‑bit
A/D Integration Time	20 ms @ 50 Hz, 16.66 ms @ 60 Hz (user‑selectable)
Conversion Time	≈ 60 ms per channel @ 50 Hz
Galvanic Isolation	Measurement circuit to backplane (VDE 0160)
Backplane Current	≈ 0.15 A (150 mA) @ 5V
Ambient Temperature	0°C to +60°C
Weight	approx. 0.20‑0.33 kg

Configuration and Application in Legacy S5 Systems

This module includes a DIP switch block for selecting line frequency (50/60 Hz) and enabling wire‑break detection. When activated, the broken‑wire function illuminates a front‑panel LED and sets a status bit for diagnostics. The Siemens 6ES5464-8MF21 is ideal for temperature monitoring in legacy applications such as engine exhaust, bearing housings, and process vessels. Therefore, it remains a key component for maintaining dependable S5 automation infrastructure.