4G remote monitoring of unmanned sites: architecture and checklist

Pumping stations, reservoirs and machines at customer sites often have power but no wired network. A cellular link is then the practical way to get data out and alarms through. This article describes 4G remote monitoring of an unmanned site layer by layer: what runs on site, how to build the connection, how to handle power, alarms and lost connections, and which ICP DAS devices fit.

A 4G remote monitoring architecture in three layers

• On site: I/O modules, meters and sensors, plus an edge controller that collects the values, runs local logic and handles communication.
• Link: a 4G modem or router, built into the controller or installed separately, with a SIM card and an antenna.
• Central: software that stores and displays the data and distributes alarms, such as SCADA, an MQTT broker with a database, or IoTstar.

Keep control decisions at the site. Stopping a pump on dry-running or starting a fan on high temperature should not depend on the mobile network. The cellular link is for reporting, supervision and maintenance access.

Build the connection from the site outwards

Most mobile subscriptions give the SIM a private IP address behind the operator's NAT. A central server cannot open a connection to the site, so the site has to connect out. Three patterns are common:

• Push data from the site. The controller publishes to an MQTT broker or sends data to a server. This works with standard SIM cards. Use MQTT over TLS (port 8883) where the device supports it.
• VPN tunnel. The site router or controller builds a tunnel to a central VPN server, and central systems reach the site through it. This is needed when SCADA polls Modbus TCP or engineers need the web interface for maintenance.
• Private APN. Some operators offer private networks with fixed addresses. This ties the solution to one operator.

Do not expose Modbus TCP or a device web interface to the Internet through port forwarding. Modbus TCP has no authentication, so anyone who reaches the port can read and write values. Also consider data volume: polling every register once per second uses far more data than sending values on change or at a fixed interval.

Power, antenna and enclosure

Plan for mains failure. If the controller and router run from a DC supply with a battery buffer, the site can still report the failure and keep logging. Wire the mains-OK signal to a digital input so the outage itself becomes an alarm.

Mount the antenna outside metal cabinets and check signal quality at the actual installation point. Cabinets in direct sun get hot, so compare the operating temperature range of every component with the site conditions.

For solar-powered sites, the G-4510 power-saving PAC has a built-in solar charger for a 12 V lead-acid battery, low-voltage disconnect and an optional 4G modem module, with a stated deep-sleep consumption below 10 mA at 12 VDC. It is a programmable MiniOS7 controller rather than a browser-configured device.

Alarms and buffering when the link is down

Plan at least two alarm paths. Email and MQTT need a working data connection. SMS does not depend on a data session, which makes it a useful second path for critical alarms.

The central system should also detect silence: if a site has not reported within a set time, raise a communication alarm.

Log measurements locally with timestamps and send the logged data when the connection returns, so the central database has no gaps. Synchronise device clocks with SNTP so timestamps from different sites can be compared.

ICP DAS devices for 4G sites

Devices with built-in 4G for EMEA

WISE-5231M-4GE and WISE-2841M-4GE are edge controllers with a 4G modem specified for EMEA frequency bands (LTE FDD B1, B3, B5, B7, B8 and B20, plus 3G WCDMA). They run IF-THEN-ELSE rules, log data to a built-in 32 GB microSD card, publish over MQTT with SSL and send alarms by email and SMS. Both read RS-485 and Modbus TCP I/O modules, accept 12 to 48 VDC and operate from -25 to +75 °C. WISE-2841M-4GE adds VPN, HTTPS, SFTP/FTPS and SNMP v3.

PMC-5231M-4GE is a power meter concentrator with the same EMEA bands. It reads ICP DAS Modbus power meters, logs to microSD and sends back log files automatically when the network connection is restored.

GRP-540M-4GE is an Ethernet, serial and CAN to 4G gateway with router and port mapping functions and the LTE bands B1, B3, B5, B7, B8 and B20.

Ethernet devices behind an industrial 4G router

Any Ethernet-connected ICP DAS device can also be installed behind a standard industrial 4G router. UA series communication servers such as UA-5231M collect Modbus data, provide OPC UA and MQTT, include an OpenVPN client and recover remote database data after an offline period. ET-2200 I/O modules such as ET-2217 publish directly to an MQTT broker.

Central software and accessories

IoTstar runs on a Windows server or a virtual machine in a public cloud. It provides remote maintenance and firmware updates for WISE, PMC and PMD controllers, imports real-time and historical data into MS SQL, MySQL or Oracle, and offers dashboards with an alarm event list. External antennas such as ANT-421-05, a 4G LTE antenna with SMA connector, complete the installation.

Cellular variants and frequency bands differ by region, and several ICP DAS cellular models are sold only in specific markets. Check availability for your country with sales before you finalise the design.

Checklist before installation

• Signal quality and operator coverage at the installation point
• SIM type (public IP, private IP or private APN) and expected data volume
• Connection pattern: push to a broker or server, or VPN for polling and maintenance
• Logic that must keep running locally when the link is down
• Alarm paths and a communication-loss alarm at the central system
• Local logging and send-back after reconnection
• Power supply, battery buffer and a mains-failure input
• Cabinet temperature range and antenna position

Send us a description of your sites, signals and central system, and our technical sales team will propose a suitable setup.