VT485m / Modbus RTU slot extension

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Function and purpose

It is an extension PCB board and should be purchased separately.

Allows to monitor up to 32 Modbus RTU devices/meters/sensors. The maximum distance of a daisy chain is up to 1000 meters. Each metered value of a Modbus device is addressed individually using input registers and is shown by the system as virtual sensors. You can configure thresholds and icon representations for these elements.

It can be used with VT335t, VT336t, VT825t, and VT855t monitoring systems. A slot PCB board can be inserted inside the monitoring unit while the unit is in operation. Has an internal termination and by default, it is switched ON (if required can be turned off).

Physical description

By default, the terminator on the board of VT335t, VT825t, and VT855t is always ON.

a) "RS-485 Status" - LED for displaying Modbus RTU port status.

b) "B-, A+, GND" - port for connecting Modbus RTU devices.

Connecting Modbus RTU sensors:

Example 1: Daisy chain connection (the main controller is located at the beginning of the chain)

• Sensors are connected in a daisy chain connection.

• 120Ω resistor is used at the end of the chain which is equal to the resistance of the cable.

• A twisted pair cable is used for A(+) and B(-).

• "VT335t, VT825t, and VT855t monitoring units" have an internal termination, and by default, it is switched to the ON position. (If it is required, it is possible to switch it OFF)

• Up to 32 devices can be used.

• Overall cable length is no more than 1000 meters.

Physical description

Example 2: (Not recommended) Daisy chain connection (the main controller is located in the middle of the chain)

"VT335t, VT825t, and VT855t monitoring units" have an internal termination, and by default, it is switched ON.

• Switch off the Vutlan monitoring unit.

• Open the enclosure’s bottom and pull the mainboard from the enclosure.

• Find a Modbus jumper and take the cap off.

• Put everything back together.

Now it is possible to connect the Modbus sensors in a daisy chain with the Vutlan monitoring unit in the middle of the chain.

• Sensors are connected in a daisy chain connection.

• 120Ω resistor is used at the ends of the chain which is equal to the resistance of the cable.

• A twisted pair cable is used for A(+) and B(-).

• Up to 32 devices can be used.

• Overall cable length is no more than 1000 meters.

Activation and Configuration of Modbus interface

After all Modbus devices have been connected to it, you need to activate it and configure:

Accessories

Some recommended readers https://vutlan.atlassian.net/wiki/spaces/DEN/pages/707788801 tested by Vutlan

Testing VT485m PCB using two Vutlan controllers

This section is useful for installers.

You can test the VT485m PCB using x2 Vutlan monitoring units.

1. Install VT485m on Vutlan monitoring system A and Vutlan monitoring system B.

2. Connect B- to B-. Connect A+ to A+.

3. Activate Modbus RTU settings on both systems. You can leave all settings by default on both systems. Web UI >> Preferences panel >> Modbus RTU tab >> Enable Modbus RTU

4. Web UI >> System tree panel >> Add element “+” sign >> Modbus RTU (reading) >> Leave all settings by default >> Additional tab >> Test button

The VT485m which is the master will blink with a blue LED.

The VT485m which is the slave will blink with a red LED.

Test complete!

Copyright:

Vutlan s.r.o. (LLC)

Remote Infrastructure Monitoring and Control

43 ul.Svornosti, 821 06 Bratislava,

Slovak Republic

http://www.vutlan.com