Unitronics PLCs are some of the most widely deployed controllers in UK industry – pump stations, packaging lines, HVAC, water treatment, agricultural systems and building management. Most of them eventually need remote access. That means a router. And every router needs a SIM.
Whether you are running the Unitronics UCR router or a third-party industrial router alongside your Unitronics installation, this page covers which SIM type you need and why a standard mobile SIM will let you down.
Why you cannot use a standard SIM in a Unitronics installation
Consumer and standard business SIMs were designed for phones. A phone connects, does something, disconnects. An industrial PLC needs to stay connected 24 hours a day, often in a remote location with no one nearby to reset it.
The problems that appear quickly in the field:
- Idle suspension. Many consumer SIMs cut the connection after a period of inactivity. Your PLC is sitting there, data is moving slowly in the background, and the SIM decides nothing is happening and drops. The connection looks fine from the router side but the tunnel is dead.
- Dynamic IP. If your IP address changes every time the SIM reconnects – or just randomly – you cannot build a stable VPN tunnel. Remote access becomes unreliable. SCADA polling fails silently. Engineers turn up on site for a problem that resolved itself.
- No inbound connections. Standard SIMs sit behind carrier-grade NAT. Nothing can reach them from the outside. That kills remote programming, remote HMI access and any monitoring system that polls the device.
- Single network. Unitronics installations in water, agriculture and utilities are frequently in rural locations or industrial sites with poor indoor coverage. A SIM locked to one network will go offline when that network has an outage or poor signal. There is no fallback.
IoT SIMs solve all of these. Fixed IP, always-on, multi-network, designed specifically for unattended remote devices.
Which SIM type for your Unitronics installation
Fixed private IP SIM – the standard choice for remote access
This is what most Unitronics installers end up needing once they think it through properly. A fixed private IP SIM gives your router a consistent, permanent address on a private APN. Traffic never touches the public internet. You reach the router – and the PLC behind it – through a VPN tunnel back to your office or SCADA head-end.
This is the correct approach for:
- Remote programming of UniStream, Vision or Samba PLCs
- VPN-based remote HMI access
- SCADA systems polling Modbus TCP from a central location
- Any installation where security matters – water treatment, utilities, critical infrastructure
The UCR-ST-B5 and UCR-ST-B8 Unitronics routers both support VPN. A fixed private IP SIM is the correct pairing for either.
Fixed public IP SIM – when you need direct inbound access
Some installers prefer a public fixed IP so the router is directly reachable without a VPN concentrator at the head-end. This works and is simpler to set up initially – but it puts the router on the public internet, so firewall rules and port hardening matter.
Unitronics PLCs have been targeted by automated attacks when left exposed with default credentials. CISA issued an advisory specifically about this following incidents at water utilities in 2023. A public fixed IP must be secured properly. That means strong credentials, no default ports, firewall rules that whitelist your engineer IPs only.
Where a public fixed IP is appropriate:
- Small OEM machine fleets where the installer manages access directly
- Sites where a VPN head-end is not feasible
- Temporary or short-term deployments
Multi-network SIM – for rural, mobile or difficult sites
Our multi-network SIMs connect automatically to whichever of EE, O2, Vodafone or Three has the strongest signal at that location. No manual configuration, no steering toward a preferred network. Just the best signal available.
Unitronics installations where multi-network coverage makes a genuine difference:
- Rural pump stations and boreholes where one network may not reach reliably
- Agricultural sites – greenhouses, irrigation systems, grain dryers
- Outdoor renewable energy sites – solar farms, wind, battery storage
- Construction and temporary sites where Unitronics controls site plant
- Water treatment infrastructure in semi-rural locations
Multi-network is available with fixed IP. You do not have to choose between resilient coverage and stable addressing.
Dual SIM installations
The Unitronics UCR-ST-B8 has two SIM slots. The UCR-ST-B5 has one. For critical installations – water infrastructure, unmanned substations, remote SCADA sites – a dual SIM setup with automatic failover is the right approach. That typically means two SIMs from different networks or one multi-network SIM paired with a single-network backup.
If you are running a third-party router such as a Teltonika RUTM50 or Milesight UR75 alongside your Unitronics PLC, dual SIM failover with two independent SIMs is straightforward to configure.
We can supply matched SIM pairs for dual-SIM deployments.
Unitronics router compatibility
| Router | SIM slots | Best SIM type | Notes |
|---|---|---|---|
| UCR-ST-B5 | 1 | Fixed private IP, multi-network | Entry model, connects to UniCloud, supports VPN |
| UCR-ST-B8 | 2 | Fixed private IP x2, or fixed IP + multi-network | Dual SIM failover, RS232/RS485, GPS – the fuller industrial option |
| Third-party router (Teltonika, Milesight, etc.) | 1 or 2 | Fixed private IP, multi-network | Many Unitronics installers use third-party routers for multi-vendor sites |
Standard SIM form factor (2FF/Mini, 3FF/Micro and 4FF/Nano) is supported across all the above. If you are building for long-term unattended deployment in a harsh environment, ask about our MFF2 industrial-grade soldered SIMs.
Unitronics use cases and the SIM each one needs
Water and wastewater
Pump stations, boreholes, reservoirs and treatment works running Unitronics Vision or UniStream PLCs. Unmanned sites, often rural, often critical. Needs fixed private IP for SCADA polling and VPN-based engineering access. Multi-network coverage is important given rural locations. Dual SIM failover for any site that cannot afford downtime.
Building management
HVAC, boilers, chiller systems and energy monitoring controlled by Unitronics PLCs across commercial buildings. Usually Ethernet connected with a cellular backup or primary link where no fixed line exists. Fixed IP SIM for remote diagnostics and BACnet-over-IP access back to the BMS.
Food production and packaging
Packaging machines, conveyor systems and filling lines with Unitronics Samba or Vision PLCs. Machine builders increasingly need remote access for support without sending an engineer. Fixed IP SIM in the panel router gives the OEM a VPN back to their support desk.
Agriculture
Irrigation controllers, greenhouse environmental systems and feed automation in rural locations. Multi-network SIM is essential here – single-network coverage in agricultural areas is inconsistent. Fixed IP for remote access and data logging back to a central system.
Renewable energy
Solar farm inverter monitoring, battery storage BMS and EV charging infrastructure using Unitronics PLCs. Often unmanned, often remote. Fixed IP, multi-network, long-term deployment. MQTT telemetry back to a cloud platform alongside VPN for engineering access.
OEM machine fleets
Machine builders shipping Unitronics-controlled equipment to multiple customer sites. Each machine needs a router and SIM for remote support capability. Fixed IP SIM means the engineer can VPN to any machine in the fleet from the office. No more 200-mile service visits for a parameter change.
What we supply
- Multi-network IoT SIMs connecting to EE, O2, Vodafone and Three
- Fixed public and private IP options
- Private APN for closed-network deployments
- Standard and MFF2 industrial form factors
- Data plans from 1GB to 500GB with shared pool options for fleets
- SIM management portal – activate, suspend, monitor usage, set alerts
- UK-based technical support
We work with single-device enquiries through to national rollouts. If you are speccing connectivity for a fleet of Unitronics-controlled machines or sites, get in touch and we will advise on the right SIM type, data plan and IP configuration before you commit to anything.
Get a quote
Tell us your router model, number of sites, expected data usage and whether you need fixed IP. We will come back with a recommendation and pricing within two business hours.
Call: 01937 534 914
Email: sales@iotsims.co.uk
Or use the enquiry form on this page.
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