EATON MTL4850 HART multiplexer complete guide

CPH series backplane: Connected to redundant 24V DC power supply through two independent 4-position pluggable screw terminals. The LED indicates the power status. The "ring network" system can supply power to multiple backboards, allowing for the removal of a single backboard without affecting other backboards. The maximum circuit current is 12A.

4.2 RS485 communication connection

The MTL4850 system adopts RS485 two-wire, half duplex, differential, multi-point (up to 32 nodes) communication standards. RS485 allows network lengths up to 1000 meters and data rates between 1200 and 38400 baud.

Connection method:

Connect using shielded twisted pair cables (such as Belden 8132 or 9841).

Connect the two core wires of the cable to screw terminals A and B of backplane port A. Connect the cable shielding layer to terminal C.

If multiple backboards need to be connected, use port B loop to connect to port A of the next backboard. It is recommended to use a consistent color convention (such as red for A and black for B).

Terminal and bias:

Terminal matching: Ideally, impedance matching (usually 100-200 Ω) should be performed at both ends of the RS485 bus to prevent signal reflection and ringing.

Bias: When the bus is idle, it is in an uncertain floating state, and noise may be mistaken for valid characters. The bias resistor can place the bus in a known state to prevent false reception.

The MTL4850 module itself does not have terminal or bias functions, which are typically provided by RS232/RS485 converters.

Data Converter:

Due to the fact that most PCs use RS232 or USB interfaces, a data converter is required. Recommend using Westermo MA45 RS232/485 converter. For Ethernet connections, it is recommended to use Moxa NPort ®  5130 (RS485) or 5230 (RS485+RS232).

4.3 Signal Connection

On site wiring in hazardous areas: Connect using the blue terminal on the top of the MTL4500 module.

Connection of safety zone control system: The CPH series backplane provides two layered terminals for each channel, with corresponding channel numbers. The maximum wire diameter is 2.5mm ² (12 AWG).

HART signal cable: Use a 20 way flat cable (HM64RIB20-x.x) to connect the CPH backplane to the HMP-HM64 or HART connection unit. The maximum length is 15m.

Backplane interface bus: Use 34 flat cables (HM64RIB34-x.x) to connect two CPH-SC16 (R) backboards for channel expansion.

Module installation and configuration

5.1 MTL4850 module installation

Align the MTL4850 module with the marked connector on the backplane.

Press down evenly to ensure that the module is fully seated.

Tighten the two (built-in) installation screws.

Attention: All safe zone circuits and power connections are completed through this connector, so the module must be properly seated. If the module is not working properly, the module installation should be checked first.

5.2 Isolator module installation (if used)

Place each isolator module in its corresponding position on the backplane.

Ensure that the module is not tilted (to prevent damage to the connector pins), and then carefully press it into the backplane.

5.3 MTL4850 module configuration

5.3.1 RS485 communication rate

The speed of the RS485 interface is automatically detected within the range of 38400, 19200, 9600, or 1200 baud.

5.3.2 HART Address Setting

Up to 63 MTL4850 modules can be connected to one maintenance workstation. Each module must have a unique address, which can be set through DIP switches on the board. The switch is binary encoded and the desired address is obtained by combining the ON states of 1, 2, 4, 8, 16, and 32. For example, address 29 needs to set 16, 8, 4, and 1 to ON (16+8+4+1=29).

Note: HMP-HM64 can only set even addresses, and another module automatically uses the next odd address.

5.3.3 Power on operation

PWR LED: should light up.

Normal operation: The FAULT LED should flash regularly (with equal on/off time), indicating that the scanning list of the internal HART circuit is being established or rebuilt. After this process is completed, the FAULT LED should turn off, indicating that it has entered the "running" state.

Problem indication:

FAULT LED emits short and long alternating flashes: indicating that no HART circuit has been found.

FAULT LED constantly on: indicates that a fault has been detected and the process of creating the list has been aborted.

Scan List: Each circuit connected to MTL4850 will be added to the scan list if a HART device is detected during power on or when it is reset by maintenance software. You can use the "Circuit Reconstruction" function in the maintenance software to add or remove circuits separately.

Software Connection and Integration

6.1 Communication Mode and Driver

The MTL HART system supports PC access to HART field devices for configuration, diagnosis, and performance monitoring. Regularly monitor the status of HART devices and issue alerts when the status changes. The event logs maintained internally can be accessed through device management software.

Most device management software packages are based on Device Description Files (DD) or FDT technology. MTL provides software driver files that support both methods.