MTL4850 Gateway Integration Manual

RS485 communication network configuration

The RS485 serial interface standard is the foundation for MTL4850 system to achieve long-distance and multi node communication. Unlike RS232 or USB, RS485 allows network lengths to extend up to 1000 meters, data transfer rates to operate between 1200 and 38400 baud, and supports simple parallel connections of multiple units.

Physical layer specifications

From a technical perspective, RS485 can be seen as a two-wire, half duplex, differential, multi-point (32 node) communication standard. This standard only defines the characteristics of drivers and receivers that can be connected to the bus, and does not specify cables, connectors, data rates, or signal formats.

Terminal resistance and bias

Ideally, RS485 interfaces should be equipped with "matching" terminal resistors to prevent signal reflection and ringing. Terminal resistor is usually a simple resistor whose impedance matches the characteristic impedance of the cable - typically in the range of 100-200 Ω.

When there is no communication activity on the bus, the bus is in an undefined floating state, and noise on the bus may be decoded as valid characters. Good quality software should be able to discard most of these characters, but by biasing the bus to a known state, it can further prevent the reception of false characters. It should be noted that the MTL4850 multiplexer module itself does not have terminal resistance or bias function - these are usually provided by RS232/RS485 converters.

Two wire interconnection method

The MTL4850 system adopts a two-wire connection. The same pair of cables is used simultaneously for queries sent by the master station and responses sent by the slave station. The MTL4850 module is connected to this two-wire link through the RS485 port on the backplane and to the maintenance workstation. Up to 63 MTL4850 modules can be connected to one main station maintenance workstation.

The connection operation is as follows: Use a shielded cable (such as Belden 8132 or 9841) to connect the two cores of the RS485 cable to terminals A and B of port A on the backplane, and connect the cable shielding layer to terminal C. If multiple backplates need to be connected, use port B to connect to port A of the next backplane. To avoid troubleshooting difficulties, it is recommended to use the same color convention for all backplane terminal A and B connections, such as red for A and black for B.

An important reminder: If the polarity of the signal line connection is incorrect, it will not cause equipment damage, but the system cannot operate. Simply exchange two lines to restore normal operation.

Selection of Data Converter

There are many RS232/485 data converters available on the market for selection. The widely tested and recommended model for MTL4850 conversion from RS232 to RS485 is Westermo MA45. For USB or Ethernet requirements, other converters should be selected accordingly. The Moxa NPort 5130 (RS485) or Moxa NPort 5230 (RS485+RS232) provided by MTL are good choices for converting serial ports to Ethernet.

MTL4850 module configuration and operation

Installation and wiring

Place the MTL4850 module at the marked connector position on the backplane, press it evenly until it is fully seated, and then tighten the two fixing screws (with anti loosening design). All safety zone circuits and power connections are completed through this connector, so the module must make correct contact with the backplane. If the module is working abnormally, module installation should be the first check point.

If isolator modules are installed on the backplane, please ensure that each isolator module is placed in its correct slot position. The module should not be tilted to avoid damaging the connector pins, then carefully press it onto the backplane.

HART Address Setting

Each MTL4850 module must have a unique address. Set the address using the DIP switch on the circuit board next to the module. The address switch uses binary encoding to construct the required numbers from the provided switch options: 1, 2, 4, 8, 16, 32. For example, the setting method for address 29 is to place the switches corresponding to 16, 8, 4, and 1 in the ON position (16+8+4+1=29).

It should be noted that HMP-HM64 can only be set to even addresses, as the other module will automatically adopt odd addresses.

Interface speed

The speed of the RS485 interface is automatically detected within the range of 38400, 19200, 9600, or 1200 baud, without the need for manual configuration.

Power on operation and status indication

The MTL4850 system is controlled by the upper computer running the instrument management software. Even without software, basic hardware functionality can be checked by observing the LED indicator lights on the top of MTL4850.

LED behavior during correct operation: When powered on, the power (PWR) LED should light up. The multiplexer will start building (or rebuilding) the internal scan list of the HART loop connected to it. This process is indicated by the regular flashing sequence of the faulty LED (with equal duration of on/off). At the end of this process, the fault LED should turn off, indicating that the system has entered the "running" state.