MTL4850 Gateway Integration Manual

MTL4850 HART multiplexer: A complete guide to integration, configuration, and troubleshooting

In modern process automation factories, the number of intelligent field devices continues to grow, and how to efficiently calibrate, configure, and maintain HART devices distributed throughout the factory network has become a core challenge faced by instrumentation engineers. The MTL4850 HART maintenance system is designed as a solution to address this requirement - it establishes a simple yet powerful interface to connect on-site intelligent devices with the upper computer running the HART instrument management software.

This article aims to provide a comprehensive technical guide covering the hardware architecture of MTL4850 system, integration methods of various connection schemes, construction of RS485 communication network, module configuration, and troubleshooting and daily maintenance of the system. Whether you are deploying a HART maintenance system for the first time or need to expand your existing network, this article will provide you with the practical guidance you need.

Overview of System Architecture

The core element of the MTL4850 HART maintenance system is a plug-in designed multiplexer module. This module is installed on a dedicated backplane and secured with screws to ensure a secure and reliable connection. A single MTL4850 module can accommodate up to 32 field devices and connect to a PC running HART maintenance software through an RS485 to USB or Ethernet converter. Depending on the management software, up to 63 MTL4850 modules can be connected on a serial link, which means the theoretical maximum device capacity can reach 2016 smart field devices.

The system supports use in both safe and hazardous environments. For secure area applications, the HART connection unit provides up to 32 connection terminals for on-site devices; For on-site equipment in hazardous areas, IS isolation interfaces can be used. These isolation modules are conveniently installed on the backplane and provide a connection path with the upper computer. When the isolator is installed on the backplane, the hazardous area wiring is directly terminated on the isolation module rather than the backplane, so the backplane itself does not require intrinsic safety certification.

Detailed explanation of connection scheme

The MTL4850 system provides three main HART signal connection methods, and engineers can choose the most suitable solution based on specific application scenarios and control room configurations.

Integrated Connection Unit: HTP-SC32

HTP-SC32 represents the simplest and most direct integrated solution. This connection unit is equipped with an MTL4850 multiplexer, which is a 32 channel independent unit with screw terminals for connecting field devices and the main system. Each channel provides two terminals that can be connected to two-wire transmitters, 4/20mA current loops, or voltage inputs. The channels are isolated from each other, so they can be connected to any appropriate position in the analog circuit, and the input and output types can also be mixed.

Regarding the terminal impedance requirements for HART signals: HART signals must be terminated with an impedance greater than 240 Ω. A parallel resistor installation position is reserved on the circuit board - usually using a 250 Ω resistor - and if the input impedance of the connection point is lower than 240 Ω, a series resistor can be installed. There are multiple models to choose from for different terminal options.

From an application perspective, HTP-SC32 is suitable for scenarios that require rapid deployment without the need for additional interface hardware. This unit comes with an RS485 port and redundant DC power interface, and only needs to connect a 24V power supply and RS485 link to start working. Two RS485 ports are used to connect and maintain the cascading of PC and other HTP-SC32 units.

In terms of installation, HTP-SC32 is designed for control room cabinet installation and is installed on a carrier suitable for T-shaped or G-type DIN rails at the factory, which can be installed in any direction. The weight of the carrier is 500g, the weight of the module is 120g, and the height from the top of the DIN rail after module installation is 152mm.

The power requirement is 20-35V DC, with a current consumption of 75mA when powered by 24V. A pluggable four position screw terminal connector is used to provide redundant 24V DC power connection. Each redundant power input is equipped with an LED indicator light, and a diode connected in series at the power input ensures the use of the higher voltage of the two power supplies. When one power supply fails, it can automatically switch. A 0.5A fuse provides overcurrent protection.

Modular solution based on HMP-HM64 interface

When the system requires greater expansion flexibility, the HMP-HM64 HART interface is the ideal choice. This interface is designed to connect remote connection units or backboards through ribbon cables, accommodating two MTL4850 HART interface modules, thus supporting 64 channels on its own. It can also be cascaded with other similar interfaces through RS485 links to support more channels.

HMP-HM64 is equipped with four 20 way ribbon cable connectors (P1-P4) for receiving HART signals from HCU16, HCU16AO connection units, or backplates equipped with DIN41651 connectors. Each connector provides 16 signal connections and 4 grounding circuits to the module. The dedicated HM64RIB20 ribbon cable is used for this purpose, with standard lengths ranging from 0.5 meters to 6 meters. It should be noted that this cable is designed for internal connections within the cabinet and is not suitable for environments outside the cabinet.

In terms of address settings, HMP-HM64 is equipped with a five bit DIP switch array. Due to the interface accommodating two modules, the address setting adopts an even addressing method (0, 2, 4, 8, 16, 32). The address switch defines the address of module 1, and module 2 automatically uses its previous odd address. For example, if the address switch is set to 24 (switches 8 and 16 are turned on), module 1 uses address 24 and module 2 uses address 25.

In terms of power requirements, when both modules are installed, the current is 130mA @ 24V DC. Installation size: The weight of the carrier is 230g, and each module weighs 120g.

HCU16 and HCU16AO connection unit

The HCU16 HART connection unit provides a connection interface for on-site wiring and host/system control for safe area applications, as well as a point for accessing HART signals for maintenance systems. Each channel has three terminals: positive, negative, and transmitter power supply terminal (Tx+). Similar to HTP-SC32, HART signals must be terminated with an impedance of approximately 240 Ω, and installation positions for parallel or series resistors are reserved on the circuit board.

This unit can be used for analog output, provided that the system's current signal is compatible with HART communication. The on-site signal and system connections are completed through screw terminals. Installation size: The weight of the carrier is 330g, and the height from the top of the DIN rail is 53mm.

HCU16AO is a variant product specifically designed for analog output applications. Many systems' 4-20mA analog outputs are not compatible with HART data due to their typically low impedance. In addition, noise generated by analog output can sometimes interfere with HART data, or vice versa affect the stability of current signals. HCU16AO solves this problem in non hazardous areas by having 16 isolated channels, each of which is connected in series with a low-pass filter in the system current signal path. This filter has almost no effect on 4-20mA signals, but provides a suitable high impedance (>240 Ω) for the detection and measurement of HART signals. The on-site and system connections are achieved through pluggable eight position screw terminals, divided into four groups according to four channels per group. The weight of the unit carrier is 770g, and the height from the top of the DIN rail to the top of the screw connector is 58mm.

Integrated scheme of isolator based on CPH backplane

For application scenarios that require intrinsic safety isolation, MTL offers CPH-SC16 (R) and CPH-SC32 (R) series backboards. These backplanes are designed for the MTL4500 series analog input and output modules, with each backplane capable of accommodating 16 MTL4500 modules and one MTL4850 HART multiplexer module.

The CPH-SC16 and CPH-SC16R backboards support 16 HART channels, but by connecting a second CPH-SC16 (or 16R) backboard, the MTL4850's 32 channel capacity can be fully utilized. They are mainly designed for MTL4541, MTL4541A analog input module, and MTL4546 analog output module. The CPH-SC16R version has a 250 Ω resistor connected in parallel at both ends of the control system terminals, providing 1-5V signals to the host - this version can only use MTL4541 and MTL4541A modules.

The P1 and P2 connectors equipped at both ends of the backplane are used to connect a pair of CPH-SC16 (or 16R) backboards. When using this connection method, only the backplane with MTL4850 installed (carrying modules 1-16) needs to be connected to the RS485 serial link.

The CPH-SC32 and CPH-SC32R backboards support 32 HART channels and are mainly designed for MTL4544, MTL4544A analog input modules, as well as MTL4549, MTL4549C analog output modules. The CPH-SC32R version also has 250 Ω resistors connected in parallel at both ends of the control system terminals, and can only use the MTL4544 module.

All CPH backboards are equipped with two RS485 ports for connecting to maintenance PCs and cascading downstream to other backboards or HART interfaces. If a pair of backplane connections are used, the RS485 serial link should only be connected to the backplane where MTL4850 is installed.

In terms of power supply, the backplane provides dual redundant 24V DC power supply through independent four screw terminal connectors. Each redundant power input is equipped with LED indicator lights. The series diode at the input prevents mutual interference between two power sources, and the 0.5A fuse provides overcurrent protection. Power requirements: Voltage 20-35V DC, current consumption on CPH-SC16 (R) maximum 0.65A @ 24V DC (all channels 20mA), and maximum 1.2A @ 24V DC on CPH-SC32 (R).

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.

Possible abnormal situations: If there is a problem during the power on process, the faulty LED will emit a sequence of short and long flashes, indicating that no HART circuit has been found; Or if it continues to light up, it indicates that a fault has been detected and the list construction process has been aborted. It should be noted that the default setting of MTL4850 at the factory is "scan disabled". In any of the above situations, the scanning mode of MTL4850 can be changed through the instrument management software.

The composition of the scan list: When each connected circuit of the HART device is detected during power on, or when the instrument management software resets MTL4850, the circuit will be added to the scan list. You can use the "Circuit Reconstruction" function in the software to add or remove circuits separately. When scanning is enabled, MTL4850 continuously cycles through all circuits in the scanning list.

LED status quick reference

Power LED (green):

Off: The multiplexer is not receiving power

Lighting up: The multiplexer is receiving power

Fault LED (red):

Off: The multiplexer is in operation

Stable flicker: The multiplexer is being built/rebuilt

Short/Long Flash: HART Loop not found

Stable illumination: Fault detected, multiplexer operation has stopped

Host LED (yellow):

Extinguished: No communication on the channel

Short flash (0.25 seconds): The multiplexer receives a message in the correct format

Long flash (1 second): Response sent

HART LED (yellow): Indicates activity on the HART loop

Troubleshooting and Maintenance Strategy

Precautions for module replacement

When replacing MTL4850, HMS software will not automatically recognize the replacement device until one of the following operations is completed:

Use HMS software to make the node name (stored in MTL4850) the same as the node name of the removed device

Rebuilding the network, the software will automatically adopt the node names of the replacement devices

Replacement steps for isolator module

To replace a potentially faulty MTL4500 isolator module, please follow the following steps:

Unplug the hazardous area connector

Release the buckle and remove the module from the back panel

Insert and fix the replacement unit

Reinstall the hazardous area connector

Safety precautions for operating in hazardous areas

Most operating procedures allow for live maintenance of intrinsically safe equipment and systems, provided that appropriate measures are taken to protect the integrity of the equipment or system. When performing live maintenance on the MTL4500 module, the hazardous area connector inserted into the top of the module may need to be removed, so the cable leading to the hazardous area connector must have sufficient flexibility to easily plug and unplug the connector from the top of the module.

After unplugging the hazardous area connector, care must be taken to ensure that the connector is not placed in a position that may come into contact with the backplane or backplane components. The backplane is connected to the safe area circuit, so it is not inherently safe. Unprotected connectors may bypass the necessary isolation between safe and hazardous area circuits. This can be avoided through the following methods:

Insert the connector into the MTL4599 virtual isolator or other uninstalled MTL4500 modules (but do not insert any other modules installed on the backplane)

Provide a temporary method to fix the connector so that it cannot come into contact with the backplane or safe area circuit

Troubleshooting steps

When troubleshooting customized backplates, the following steps should be performed in sequence:

Check the installation status and confirm that no damage or deterioration has occurred

Check if the backplane power LED is lit. If not lit, check the power fuse and replace it if necessary

Check if the power LED on the MTL4850 module is lit. If the circuit board power LED lights up but the module LED does not light up, replace the module

Replace the potentially faulty isolator module

Check the integrity of the cables and the correctness of grounding

Regular maintenance checklist

It is recommended to check the general condition of the installation at least every two years, and for particularly harsh environments, the inspection frequency should be increased:

Confirm that the module type complies with the relevant documents and is installed in the correct backplane position

Confirm that the labels of the module and hazardous area connectors are correct and clear, and that the connectors are inserted into the matching module. The label details are consistent with the relevant documents

Confirm that the module and hazardous area connectors are securely plugged into their matching sockets

Confirm that all connections between the backplane and hazardous area connectors have been correctly completed

Confirm that the cables connected to the backplane and hazardous area connectors comply with the specified type and rating, are properly routed and separated, and have no wear or other damage

Confirm that the cable shielding layer is correctly grounded

Important reminder: It is strongly recommended that users only perform the testing and daily maintenance described in sections 6.2 and 6.3. If it is determined that the MTL4500 module is faulty, maintenance or modification should not be carried out as this may affect the intrinsic safety performance of the module. Any faulty unit or backplane should be returned to MTL or the representative office at the time of purchase for repair or replacement.

Interpretation of Alarm Event Log

The MTL4850 multiplexer maintains an alarm event log that can be read through the instrument management software. Event types can be classified into the following categories:

General information category:

Alarm generated by HART test command 242: MTL diagnostic test activated

No transmitter storage space: The on-site device data memory is full

Discovering HART transmitters before Rev 5: Contact the manufacturer for updated information

Detected other main stations on the circuit: there is an auxiliary main station present

Value class events that need attention:

Duplicate transmitter unique ID: This ID has already been used on the circuit, contact the manufacturer

+12V power supply out of range: Check the power specifications of the multiplexer

-12V, VBias, VLeak are out of range: usually need to return to MTL for processing

Error causing module reset:

This type of error includes CRC error, watchdog reset, clock monitor reset, memory test failure, etc. Single or occasional occurrences of these events may be due to power noise or interruptions, but multiple or frequent events may indicate installation or module issues, in which case the module should be returned to MTL for inspection.

Compatible control system

MTL offers a range of customized backplates for installing MTL4500 series IS isolators to meet specific control or safety system requirements. Many customized boards for analog I/O signals include ribbon cable connectors for connecting HMP-HM64. Typical compatible systems include:

Emerson DeltaV and DeltaV SIS systems

HIMA HiMax

Honeywell Experion C300、 Safety Manager, Process Manager I/O System

Invensys Foxboro FBM system, Triconex Tricon, and Trident system

Siemens ET200M

Yokogawa Centum R3, Prosafe RS system

Software connectivity

The MTL4850 system supports instrument management software packages based on device description files or FDT technology. MTL provides software driver files to support both methods. MTL4850 Communication DTM (Device Type Manager) enables the MTL4850 system to transmit HART data to any instrument management software that adopts the FDT/DTM concept. DD and DTM files can be downloaded for free from the MTL website.