Technical specifications
Technical specifications of the IO module: digital inputs, relay outputs and what they can switch, network and Modbus details, power, environmental limits, certifications and failsafe behaviour.
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
Channels
6 digital inputs (DI) + 6 relay outputs (DO) per module
Relay switching, max
5 A resistive / 2 A inductive per channel, at 250 VAC or 30 VDC
Contact type
Form A (normally open) power relay, potential-free
Communication
Modbus TCP (server/slave) over Ethernet, TCP port 502
Ethernet
2 × 10/100 Mbps RJ45 switch ports (daisy chain), 1 MAC address
Power supply
24 VDC nominal (12–36 VDC), 188 mA @ 24 VDC (≈ 4.5 W)
Mounting
DIN-rail or wall, 27.8 × 124 × 84 mm, < 200 g
Ambient temperature
−10 to 60 °C (standard) or −40 to 75 °C (wide-temperature model)
Isolation
3 kVDC / 2 kVrms, field to logic
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:
Maximum switching current
5 A resistive, 2 A inductive, per channel
Maximum switching voltage
250 VAC or 30 VDC (also rated at 110 VAC)
Maximum switching power
≈ 1150 W at 230 VAC or 150 W at 30 VDC (5 A resistive)
Contact type
Form A (N.O.) power relay, potential-free
Contact resistance
100 mΩ (max.); 30 mΩ initial
Breakdown voltage (open contact)
500 VAC
Initial insulation resistance
1000 MΩ (min.) @ 500 VDC
Isolation (field to logic)
3 kVDC or 2 kVrms
Relay on/off time
1500 ms (max.)
Maximum switching rate
0.3 Hz at rated load (pulse mode)
Mechanical endurance
5,000,000 operations
Electrical endurance
100,000 operations @ 5 A resistive load
Field wiring
I/O cable max. 14 AWG (≈ 2.5 mm²), screw terminal block
These ratings are per channel, not a budget for the module, and they are switching limits — not continuous-duty design targets. The inductive rating (2 A) is less than half the resistive one, and motors, pumps, fans, transformers, contactor coils, capacitor banks and LED drivers draw an inrush current several times their nominal current, which erodes the contacts quickly. Size on inrush, not on nominal power, and switch anything substantial through an interposing contactor.
What you can wire directly, and what needs a contactor
230 VAC resistive load ≤ 5 A (≈ 1.1 kW) — e.g. small heater
Yes
230 VAC resistive load > 5 A (> ≈ 1.1 kW)
No — switch an interposing contactor
400 VAC (three-phase) load, any size
No — contacts are rated 250 VAC max; use a contactor
Inductive AC load ≤ 2 A (small coil, small pump)
Possible; add an RC snubber across the contact
Inductive AC load > 2 A (motor, fan, transformer)
No — use a contactor, sized for the load's inrush
DC load ≤ 30 VDC and ≤ 5 A resistive (≤ 150 W)
Yes — for inductive DC loads keep to 2 A and add a flyback diode
DC load above 30 VDC
No — outside the contact rating
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)
Channels
6, sharing one common (6 points per COM)
Sensor type
Dry contact, or wet contact (NPN or PNP)
Dry contact
On = short to GND, Off = open
Wet contact (DI to COM)
On = 10–30 VDC, Off = 0–3 VDC
Input mode
Digital input or event counter
Counter frequency
250 Hz (max.), counter value retained on power loss
Digital filtering
Software selectable filter time
Isolation
3 kVDC or 2 kVrms
Field wiring
I/O cable max. 14 AWG (≈ 2.5 mm²), screw terminal block
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:
1
COM 0
11
R1_NO
2
DI0
12
R1_C
3
DI1
13
R2_NO
4
DI2
14
R2_C
5
DI3
15
R3_NO
6
DI4
16
R3_C
7
DI5
17
R4_NO
8
GND
18
R4_C
9
R0_NO
19
R5_NO
10
R0_C
20
R5_C
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
Ethernet ports
2 × 10/100BaseT(X) RJ45, built-in switch (daisy chain), 1 MAC address
Ethernet protection
1.5 kV magnetic isolation
Protocol used by the EMS
Modbus TCP (the module is the server/slave), TCP port 502
Other protocols
TCP/IP, UDP, DHCP, BOOTP, HTTP (web console), SNMPv1/v2c
Addressing
Fixed (static) IP address required; note IP, port and Modbus slave ID
Factory default
IP 192.168.127.254, netmask 255.255.255.0, no gateway
Configuration
Browser-based web console on the module's IP address
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:
DI value, channel 0–5
FC 2 (read discrete inputs)
0x0000–0x0005 (ref. 10001–10006)
DI value, all 6 channels in one word
FC 4 (read input registers)
0x0030 (ref. 30049), bit 0–5
DI counter value, channel 0–5
FC 4 (read input registers)
0x0010–0x001B (2 words per channel)
Relay output value, channel 0–5
FC 1 (read), FC 5 / FC 15 (write)
0x0000–0x0005 (ref. 00001–00006)
Relay output, all 6 in one word
FC 3 (read), FC 6 / FC 16 (write)
0x0020 (ref. 40033), bit 0–5
Watchdog alarm flag
FC 1 (read), FC 5 (write 1 to clear)
0x1030 (ref. 04145)
Failsafe behaviour and watchdog
Power loss
All relays de-energize; the normally-open contacts open. This needs no configuration: the contacts cannot stay closed without coil power.
Communication loss, watchdog disabled (factory default)
Every output holds the last value the EMS gave it. A controller crash or a broken network therefore changes no relay at all, as long as the module stays powered.
Communication watchdog
Optional, disabled by default. When enabled with a timeout, the module enters safe mode after that long without Modbus TCP communication. The EMS polls the module every control cycle, which keeps the watchdog satisfied while the controller is alive.
Safe status per output
Each output has its own safe state (Hold Last, ON or OFF), applied when the module enters safe mode. It has no effect at all while the communication watchdog is disabled.
Safe status latch
Once a channel has entered safe mode, its safe status stays latched until it is cleared. The EMS polls the module's watchdog alarm flag, reports it as a device error and clears it once the module is reachable again.
Idle connection timeout
The module releases an idle Modbus TCP connection after a configurable interval, freeing the socket for a new one.
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.
The module is not a certified functional-safety device: it carries no SIL or performance-level (PL) rating, and its relays are not safety relays. Where a rated safety circuit is required, the relay output should command a safety relay or contactor that provides that rating, and the safety function must be assessed against the applicable standards (for example EN 60204-1 and EN ISO 13850).
Power supply
Power input
24 VDC nominal, 12 to 36 VDC
Power consumption
188 mA @ 24 VDC (≈ 4.5 W)
Connection
Screw terminal block on the top panel, with ground pin
Earthing
Connect the ground pin to the cabinet earth
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
Dimensions (W × H × D)
27.8 × 124 × 84 mm
Weight
< 200 g
Housing
Plastic
Installation
DIN-rail or wall mounting
Operating temperature
−10 to 60 °C (standard model)
−40 to 75 °C (wide-temperature model)
Storage temperature
−40 to 85 °C
Ambient relative humidity
5 to 95%, non-condensing
Altitude
Up to 4000 m
The relays may malfunction in condensing environments below 0 °C. In unheated or outdoor cabinets, provide heating or dehumidification, and choose the wide-temperature model.
Standards, certifications and reliability
Safety
UL 508
EMC (EMI/EMS)
EN 61000-6-2, EN 61000-6-4, EN 55032/EN 55024, FCC Part 15 Subpart B Class A
Immunity
EN 61000-4-2/-4-3/-4-4/-4-5/-4-6/-4-8/-4-11
Shock / vibration / freefall
IEC 60068-2-27 / IEC 60068-2-6 / IEC 60068-2-32
Hazardous locations
Class I Division 2 / ATEX Zone 2 (variant-dependent — verify for the model supplied)
Environmental
RoHS, CRoHS, WEEE
MTBF
808,744 hours (Telcordia SR-332)
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.
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