9 Rules for Correct Cabling of the Modbus RS485 Communication Systems

The cable to be used is a shielded twisted pair (telephone type). The cable to be used is a shielded twisted pair (telephone type). The maximum number of devices that can be connected to a main cable is 32, including the Master. Henceforth, we shall consider Slave devices to be measuring instruments with serial communication, even if the cabling is similar for all Modbus devices. RS-485, also known as TIA-485(-A) or EIA-485, is a standard, originally introduced in 1983, defining the electrical characteristics of drivers and receivers for use in serial communications systems. The module communicates with Be1 via an RS485 serial interface that supports the MODBUS-RTU protocol. The panel consists of basic ingredients: a Be1 generator controller, a general-purpose interface relay board, a state-of-art GSM Be148-1 gateway and a multiband MODEM. The BE1 GSM panel includes the Be1 generator controller, the Be148-1 SMS gateway module, a GSM modem, cables, an antenna and interface boards with removable connectors. Using a repeater, the main cable is divided into different segments, each of which can be up to 700 m in length and connect 32 devices (this number includes the repeaters). The equipment located along a set of RS-485 wires are interchangeably called nodes, stations or devices.

Grounds between buildings may vary by a small voltage, but with very low impedance and hence the possibility of catastrophic currents - enough to melt signal cables, PCB traces, and transceiver devices. Star and ring topologies are not recommended because of signal reflections or excessively low or high termination impedance. You can set up an automatic start based on low battery voltage. Set the Be1 in OFF mode. It commands the BE1 to shut down the engine by entering the OFF mode. After 2 minutes you must receive the SMS MODE OFF; ENGINE OFF; NO ALARMS. To get real-time measurements via SMSB, you must connect a Fuel Level Sensor. You will get an automatic notification every 10% change in the fuel level. According to the settings made on Be1, the panel will send all information gathered about analogue measurements of temperature, oil pressure and fuel level. You can connect here, in logic 'OR' fashion, start requests coming from the pressure switch, level switch, and a relay suitable for your application.

TSB-89A, Application Guidelines for TIA/EIA-485-A does not recommend using star topology. RS-422 and RS-485 Standards Overview and System Configurations, Application Report (pdf). In theatre and performance venues, RS-485 networks are used to control lighting and other systems using the DMX512 protocol. These characteristics make RS-485 useful in industrial control systems and similar applications. It is also used in Digital Command Control (DCC) for model railways. Be1-GSM panel instructs the engine to start and stay running until a STOP command is detected. In case of a GSM issue, failure of the antenna, or SIM card, the Be1-GSM panels turn on a red alarm light. The green indicators ‘Power’ and ‘Online’ will turn on. Once you send the configuration SMS, the internal Be148-1 gateway will automatically run the installation. When the Be1-GSM panel detects a valid SMS, the yellow indicator SEND RECEIVE turns on for a second. After a successful setup procedure, the GSM IS ONLINE green light turns on. After that, the SYSTEM SETUP illuminates to indicate the modem initialization sequence.

You can observe the modem status by looking at its three LED indicators. Under some conditions it can be used up to data transmission speeds of 64 Mbit/s. Longer branches could cause signal reflections and generate disturbances and consequent errors in the reception of data. The main cable must be no longer than 700 m! This with WiFi transmission for the Standard version, and in the RF version also with radio transmission at 433MHz (covering longer distances and with less battery consumption thanks to special optimizations). 23 to the battery minus, the Be1 will start the engine (hardware REMOTE START input). You must watch the battery when a generator is placed in a remote place. If not, you must disable it by using a mobile phone. You can pay using a bank transfer after receiving the details for issuing the proforma invoice. Two fully configurable relays can be used for various special functions as described in the "PROGRAMMABLE OUTPUT" section of the user manual. If A is negative with respect to B, the state is binary 1. The reversed polarity (A positive with respect to B) is binary 0. The standard does not assign any logic function to the two states.

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