Each fieldbus module FM33xx can be connected to 12 or 32 thermocouples. The wiring for these thermocouples is packaged in a small waterproof housing with PROFIBUS DP interface at a transmission rate of 12 Mbaud. Data exchange is mostly circular, although the non-circular service protocol (DP-V1) can also be used for parameter setting and diagnostics.

The circuit of the module can be connected with the thermocouple sensor by 2-wire connection. The linearity of the whole temperature range is achieved by a microprocessor. The temperature range can be arbitrarily selected. The fault LED indicates the disconnected status. Cold end compensation is achieved by a temperature measuring line within the connector, which means that a standard extension cable can be connected. The fieldbus module is equipped with a reverse voltage protection circuit to prevent external voltage from being applied to the thermocouple input. Maximum resistance voltage of the module is 230 V AC. Unaffected thermocouple inputs remain in normal operation or are affected only momentarily.

The extension parameters can be set through the fieldbus or KS2000 software tools via the configuration interface. The parameters are saved in the module. The status of the fieldbus module is indicated by the LED.

The Beckhoff offers several models of FM33xx fieldbus modules, which differ in the number of available thermocouple input channels (12 or 32 channels), thermocouple type (J or K), and housing type (spring-snap type A housing or additional Type B housing). The additional housing (Type B) has two tenons and a continuous rubber seal, providing an IP 65 connector with a guard for connection to socket elements. In addition, the Type B housing has two perforated brackets for mounting the FM module on the mounting plate (through hole mounting).