The MTL8000 Process I/O system for Zone 2 or Division 2 hazardous areas has received a timely boost with the availability of the 8502-BI-DP Profibus Turbo BIM (Bus Interface Module). The version-2 BIM firmware offers major improvements in the overall response time, whilst user parameterisation from the Profibus host allows for selection of logical modules in the Profibus configurator which match the physical modules fitted on the MTL8000 node.

With Profibus-DP a normal maximum of 244 bytes is allowed in the cyclic input telegram which limits the number of process and status variables that can be supported. To overcome this limitation the MTL8502 Profibus BIM supports a HART mailbox. In the output frame the user sets the module slot and channel for the data required. The BIM responds with the module slot and channel followed by the HART Status and four process variables for the channel. The BIM can then cyclically poll channels for HART data, and since the HART update time for an 8-channel module is a few seconds, it does not require to be updated with every Profibus cycle.

Using the new BIM, HART enabled field instruments can be monitored via the LAN for all four Process Variables and the 4/20mA signal using one I/O channel. As an example, when using Smart valves, the travel of the control valve dictated by the 4/20mA drive signal can be monitored by the BIM as one of the HART variables allowing the actual valve position to be displayed on the HMI faceplate. To achieve the same functionality using conventional I/O would require the additional cost of a valve travel transmitter and an AI channel. Additionally, as four process variables are available, other information such as flow, density, pressure and temperature data can be read from HART field devices.