EATON MTL4850 HART multiplexer complete guide

Eaton MTL4850 HART multiplexer: the core hub for intelligent field device management

System Overview

1.1 System Functions and Positioning

The MTL4850 HART maintenance system enables users to calibrate, configure, and maintain intelligent field devices for the entire network from a single workstation. The core of the system is the MTL4850 module, which provides multiplexing functionality for various field devices, allowing each device to be addressed and recognized from the workstation.

Another important component of the system is the terminal circuit board, which simplifies the interconnection of field devices to the MTL4850 module. MTL offers a range of terminal boards and backplates to meet most general application needs, as well as customized versions for specific OEM and application designs.

1.2 System Capacity and Scalability

One MTL4850 HART multiplexer module can accommodate up to 32 field devices. These modules are connected 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 to a serial link, which means a single system can support up to 2016 smart field devices.

Detailed explanation of system components

The MTL4850 system adopts a modular design and provides multiple connection solutions based on application requirements and on-site explosion-proof levels.

2.1 Core module: MTL4850 multiplexer

The MTL4850 module is the core of the system and adopts a plug-in design, firmly installed on the backplane through fixing screws. There is an LED indicator light at the top of the module for status indication:

PWR (green): Power indicator

Fault (red): Fault indication, flashing mode indicates different states (such as establishing scan list, not finding HART loop, detected fault, etc.)

HOST (yellow): Host communication indicator

HART (yellow): HART communication indicator

2.2 Connecting units and interfaces

2.2.1 HTP-SC32 Integrated Connection Unit

HTP-SC32 is a 32 channel integrated solution with an onboard MTL4850 multiplexer, suitable for non explosion proof areas (safe zones). It uses screw clamp terminals to connect on-site equipment and systems, with each channel isolated and capable of connecting two-wire transmitters, 4-20mA current circuits, or voltage inputs. The HART signal requires an impedance of>240 Ω to be connected, and the board has reserved a position for installing parallel resistors (usually 250 Ω) or series resistors.

Installation: Suitable for T-shaped or G-type DIN rails, can be installed in any direction. The weight of the carrier board is 500g, and the weight of the module is 120g.

Power supply: Redundant 24V DC input, connected through pluggable 4-position screw terminals. The LED indicates the power status. Power consumption: 75mA @ 24V DC.

RS485 communication: Two RS485 ports are provided for connecting the upper computer PC and cascading other HART interface devices.

HART address setting: Set the unique HART address of MTL4850 using binary encoding through the 6-digit DIP switch (SW1) on the board.

2.2.2 HMP-HM64 HART Interface

HMP-HM64 is a compact interface used to connect connection units and maintenance systems. It can accommodate two MTL4850 modules, support 64 channels, and can cascade more modules through RS485.

Connection: Receive HART signals from HCU16 or HCU16AO connection units through four 20 way flat cable connectors (P1-P4). P1/P2 connection module 1, P3/P4 connection module 2.

Installation: DIN rail installation, with a weight of 230g for the carrier board and 120g for each module.

Power supply: redundant 24V DC, power consumption 130mA @ 24V DC (dual module).

Address setting: Set two MTL4850 addresses using a 5-digit DIP switch (SW1). HMP-HM64 can only set even addresses (0, 2, 4, 8, 16, 32). Module 1 uses this even address, and module 2 automatically uses the next odd address.

2.2.3 HCU16 HART Connection Unit

HCU16 provides on-site wiring to the host/system control interface for non explosion proof areas, and also provides a HART signal outlet for maintenance systems. Each channel has three terminals:+ve, - ve, and transmitter power supply terminal (Tx+).

Installation: DIN rail installation, carrier weight 330g, height 53mm.

Connection: Connect to HMP-HM64 through a 20 way flat cable connector.

2.2.4 HCU16AO HART Connection Unit (for Analog Output)

The 4-20mA analog output impedance of many systems is too low to transmit HART signals properly, and output noise may interfere with HART data. HCU16AO is designed specifically to solve this problem, with 16 isolated channels, each of which is connected in series with a low-pass filter in the current signal from the system. This filter has almost no effect on 4-20mA signals, but presents a high impedance of>240 Ω for HART signals, making it easy to detect and measure.

Installation: DIN rail installation, carrier weight 770g, height 58mm.

Connection: The on-site and system connections are completed through pluggable 8-bit screw terminals (4 sets, 4 channels per set). Connect to HMP-HM64 via 20 flat cables.

2.3 Intrinsic Safety (IS) Application Backboard

For hazardous area applications that require intrinsic safety explosion-proof, MTL provides backplates that can be used in conjunction with MTL4500 series isolators.

2.3.1 CPH-SC16 (R) and CPH-SC32 (R) Backboards

These backboards are designed specifically for MTL4500 series analog input/output modules, capable of accommodating 16 MTL4500 modules (CPH-SC16) or 32 MTL4500 modules (CPH-SC32), and each board carries one MTL4850 module.

CPH-SC16: It is mainly used in conjunction with MTL4541/MTL4451A (single channel analog input) and MTL4546 (analog output).

CPH-SC16R: Pre install a 250 Ω resistor on the control system terminal to provide 1-5V signal to the host, only MTL4541/MTL4451A module can be used.

CPH-SC32: It is mainly used in conjunction with MTL4544/MTL4544A (dual channel analog input) and MTL4549/MTL4549C (analog output).

CPH-SC32R: Pre install a 250 Ω resistor on the control system terminal, only MTL4544 module can be used.

Connection and Expansion:

Two CPH-SC16 (R) backboards can be cascaded with 34 flat cables through P1/P2 connectors to utilize the 32 channel capacity of MTL4850. Only the backplane with MTL4850 needs to be connected to an RS485 link.

All backboards provide two RS485 ports for cascading.

Provide redundant 24V DC power input, LED indication, with 0.5A fuse protection. The maximum current of CPH-SC16 (R) is 0.65A @ 24V DC, and the maximum current of CPH-SC32 (R) is 1.2A @ 24V DC.

Address setting: Set the HART address of MTL4850 through the 6-digit DIP switch (SW1) on the board.

2.4 Installing Accessories

MTL provides a variety of installation accessories to facilitate the installation and labeling of backboards:

Surface mounting kit (SMS01): used to install the backplate on the panel, including M4 x 20mm screws, locking washers, flat washers, 10mm spacer columns, and washers.

DIN Rail Installation Kit (DMK01/DMK04): Used to install the backplate on a DIN rail, including mounting screws, locking washers, flat washers, spacer posts, washers, and mounting feet.

Tag Strip Kit (TSK18): Used to install tag strips above the backplane secure area connection for easy channel identification.

Grounding Rail Kit (ERK18): Used to connect hazardous area cable shielding layers or spare wire pairs, installed on the back panel at the same height as the top of the module.

Safety information and installation precautions

3.1 General safety precautions

Hazardous area restrictions: Equipment must not be installed in hazardous areas unless it is certified and marked for use in hazardous areas or protected by locally recognized explosion-proof technology.

Comply with local regulations: Ensure that all installation work complies with local standards, operating procedures, and on-site regulations.

Intrinsic safety system verification: Check whether the equipment in hazardous areas complies with the descriptive system documents. If you have any questions, please refer to the certificate or contact MTL for confirmation.

Functional correctness: Check whether the functionality of the interface unit is suitable for the application scenario.

3.2 Precautions for Maintenance of Intrinsic Safety Isolator Modules

Most operating procedures allow for live maintenance while maintaining the integrity of intrinsically safe equipment or systems. When maintaining the MTL4500 module with electricity, it is necessary to plug and unplug the hazardous area connector on the top of the module, so the cables on the connector should have a certain degree of flexibility for operation.

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

Immediately insert the connector into the MTL4599 virtual isolator or other uninstalled MTL4500 module after unplugging (but do not insert any other modules already installed on the backplane).

Provide a method for temporarily fixing connectors to prevent them from contacting the backplane or safe zone circuits.

3.3 Post installation inspection

It is recommended to regularly (at least once every two years, and more frequently in harsh environments) check the installation condition:

Is the module type correct and installed in the correct position on the backplane.

Whether the labels of the module and hazardous area connectors are correct and clear, whether the connectors are inserted into matching modules, and whether the label information is consistent with the document.

Are the modules and hazardous area connectors securely inserted.

Is the connection between all backboards and hazardous area connectors correct and reliable.

Whether the cable type and rating are correct, whether the wiring is reasonable, and whether there is wear or damage.

Is the cable shielding layer properly grounded.

Electrical connection

4.1 Power Connection

HTP-SC32/HMP-HM64: Connect redundant 24V DC power supply through 4-position pluggable screw terminals. The terminal allocation is shown in Figure 4.3. The LED indicates the power status.

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.

DD file: For example, when integrating the MTL4850 multiplexer in Emerson AMS software, the MTL4850 DD file needs to be applied.

FDT/DTM: For software that uses FDT technology (such as Endress+Hauser and Metso's Fieldcare), MTL provides MTL4850 Communication DTM (Device Type Manager), which enables the MTL4850 system to transfer HART data to any device management software that uses FDT/DTM concepts.

Both DD and DTM files can be downloaded for free from the MTL official website.

6.2 Alarm Event Log

The multiplexer maintains an alarm event log that can be read through device management software. Event types can be divided into:

General information: Internal parameters or values of the multiplexer.

Causing diagnostic errors in resetting.

Common log messages and their meanings (excerpt):

Meaning of log messages/required operations

Alarm generated by HART test command 242 MTL diagnostic test activation

Found a pre Rev 5 HART transmitter to check if there are any updates from the manufacturer

Other master detected on loop detected secondary master

Duplicate Transmitter Unique ID. Used on loop to check if the manufacturer has updated

!+12V Supply out of range check the power supply. If it continues to alarm, it needs to be repaired

An internal watchdog reset occurred. If the alarm persists, it needs to be repaired

Background RAM word test failed. If the alarm persists, it needs to be repaired

Single or occasional events may be caused by noise or power outages, but multiple or frequent events may indicate installation issues or module failures, requiring the module to be returned to MTL for investigation.

Typical compatible system

MTL offers a range of customized backplates for specific control or safety systems, used for installing MTL4500 series intrinsic safety isolators. These custom boards typically include flat cable connectors for connecting HMP-HM64. A typical system includes:

Emerson DeltaV and DeltaV SIS

HIMA HiMax

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

Invensys Foxboro FBM、Triconex Tricon & Trident

Siemens ET200M

Yokogawa Centum R3、Prosafe RS

You can contact MTL for customization according to specific needs.

Troubleshooting

When a problem occurs, you can follow the following steps to troubleshoot:

Check installation condition: Confirm that there is no damage or aging.

Check the power LED on the backplane: If it doesn't light up, check the power fuse.

Check the PWR LED of MTL4850: If it is not lit but the backplane power LED is lit, replace the MTL4850 module.

Replace the suspicious isolator module:

Unplug the hazardous area connector.

Remove the module from the backplane.

Install and secure the new module.

Reinsert the hazardous area connector.

Software processing after MTL4850 replacement: After replacing MTL4850, the device management software needs to perform any of the following operations to recognize it:

Use software to change the node name (stored in MTL4850) to match the removed device.

Rebuilding the network, the software will automatically adopt the node names of the new modules.