Technical specifications

This page lists the technical data of the IO module used by the Voltmasters EMS: what the digital inputs accept, what the relay outputs can switch, and the electrical, network and environmental limits you need when designing and wiring the cabinet.

For what the IO module is and how it is configured, see IO module. For placement and cabling, see Placement and cabling.

At a glance

Relay outputs and maximum switching capacity

Each of the six outputs is a potential-free Form A (normally open) contact with two screw terminals of its own: R0_NO and R0_C up to R5_NO and R5_C (see Terminal block). There is no NC terminal, so the actuation modes that assume normally-closed contacts (NC-ON, NC-OFF) only describe an installation where an interposing relay provides that contact. This is the hard limit of what one output can switch:

What you can wire directly, and what needs a contactor

In practice: use the relay output as a command contact for switchgear (contactor coil circuit, an EPO/stop input, an enable input) rather than as the power switch of the load itself. A separate contactor also keeps the cabinet's power wiring away from the module.

Digital inputs (DI)

The EMS reads every input each control cycle and logs its transitions, so the contact position is always visible on the platform. It is acted on in exactly two places: as an emergency-stop trigger, and as a breaker position that the EMS reports to the grid operator as DSO RTU telemetry. An input assigned to neither is monitoring only.

An input is never the feedback of something the EMS itself switches. The on/off state of a controllable load comes from reading the relay output back and mapping it through that port's actuation mode, not from a digital input.

A trigger input has to read high in normal operation and low for an emergency stop. The most predictable arrangement is a wet contact: a normally-closed contact feeds 10–30 VDC to the input, measured against the shared COM 0 terminal, and opening that contact drops the input to 0 V. Whichever arrangement you use, verify on the platform that the input reads back as expected in both positions before relying on it.

Terminal block

The inputs and relays share one removable 20-pin screw terminal block, numbered top to bottom:

Each relay channel has exactly two terminals, NO and C (common), and no NC terminal. The 24 VDC supply and the ground pin sit on a separate terminal block on the top panel. Screw torque 3 lb-inch.

Network and protocol

The two Ethernet ports form a small switch, so modules can be daisy-chained instead of each needing its own switch port. Keep in mind that a daisy chain is a single path: a module that loses power interrupts the modules behind it.

Default Modbus mapping

The EMS reads and writes the module every control cycle (≈ 1 second) using the default address map:

Failsafe behaviour and watchdog

Enable the communication watchdog and the per-channel safe status for every output that carries an emergency stop, whatever its actuation mode. Without them, only a loss of the module's own supply drives the relay to a defined state; a controller or network failure simply leaves the relay where it was. Set the channel's safe status to the value that means stop: OFF for a de-energize-to-stop mode (NO-ON, NC-OFF), ON for an energize-to-stop mode (NO-OFF, NC-ON). With an energize-to-stop mode the watchdog is the only thing that can enforce the stop when the link is down. See Safety and requirements.

Power supply

Size the 24 VDC supply for all modules in the cabinet, and keep the emergency-stop chain in mind: if the stop relies on the module being powered, the supply is part of that chain.

Mechanical and environmental

Standards, certifications and reliability

Sizing and design notes

• 6 in, 6 out per module. Need more channels, or channels in another cabinet? Add a module, see Placement and cabling.
• Switching latency. The EMS re-evaluates outputs every control cycle (≈ 1 s) and the relay itself takes up to 1500 ms, so allow roughly 2.5 s from decision to contact change. The outputs are not suitable for fast or continuous cycling: the maximum switching rate is 0.3 Hz at rated load.
• Contact life. 100,000 operations at full load is the electrical limit. For a load that is cycled often (a controllable load following PV surplus), the minimum runtime per activation setting protects the relay as much as it protects the load. See Controllable loads.
• Keep the relay a command contact. Interposing contactors keep load current, inductive loads and 400 V circuits out of the module.
• One fixed IP per module, and record IP, port and Modbus slave ID: you need them when adding the device on the platform.

Next steps

• IO module: adding the module on the platform and configuring its ports.
• Placement and cabling: placement and cabling across cabinets.
• Emergency stop: wiring and configuring a hardware emergency stop.
• Controllable loads: switching an on/off load through a relay output.