KL3228 by Beckhoff

The KL3228 is a resistance measurement terminal produced by Beckhoff within the KL Analog Input Modules series. It occupies a single slice on a DIN rail and connects to the internal K-Bus, allowing a PLC to capture temperature data from platinum sensors in the field. The module converts RTD resistance measurements into digital values that the automation system reads through its process image, making it suitable for precise thermal monitoring on machines, HVAC skids, and process vessels.

Each channel is factory parameterized for PT1000 elements, and the module accepts 8 individual sensors to provide multipoint feedback without external multiplexers. The housing is only 35 mm wide on the DIN rail, allowing high-density installation in any supported mounting orientation. The isolation voltage between the field and logic sides is rated at 500 V, and the terminal typically draws 85 mA from the K-Bus. This current must be included in the overall backplane power budget for the I/O segment. The input process image transfers eight status bytes and eight data words, while the minimum input memory requirement is 3 bytes per channel, providing compact data exchange with the controller.

The measuring circuit supplies a constant 0.5 mA to each channel, minimizing RTD self-heating and supporting a resolution of 0.1 °C per digit. Field wiring uses a 1-wire connection, simplifying cable runs in applications where the resistance of longer sensor leads is acceptable. The terminal supports operation at up to 95% noncondensing relative humidity. Its molded enclosure is rated IP20, so the module must be installed inside a suitable control cabinet. Output data paths can be activated to add eight optional control bytes alongside the eight data words, although the default configuration does not require user output bytes. All operating power is supplied through the K-Bus, and the module maintains full performance in any supported orientation on the DIN rail.