IONA Niagara 4 Controller I/O: Onboard Points and Expansion Options
The IONA Niagara 4 controller has 24 onboard I/O points (6 UI, 6 DI, 4 DO, 8 AO) and expands through a dedicated RS-485 eBMS/IO bus.
Onboard I/O is what sets IONA apart from a JACE, which has no physical I/O at all. This guide explains exactly what each IONA input and output can do, how to wire and configure them in Niagara 4, how they affect licensing, and how to add more I/O when a plant needs more than 24 points.
IONA onboard I/O summary
| Type | Quantity | Supported signals |
|---|---|---|
| Universal inputs (UI) | 6 | 0–10 V, 4–20 mA, NTC thermistor, monitored input, digital input, pulse |
| Digital inputs (DI) | 6 | Volt-free digital input, pulse counting |
| Digital outputs (DO) | 4 | Relay, maximum 5 A at 230 V |
| Analogue outputs (AO) | 8 | 0–10 V, 20 mA maximum, no relay drive |
| Total | 24 |
Alongside the I/O, the controller has 2 Ethernet ports, 2 general-purpose RS-485 ports, 1 RS-485 port dedicated to eBMS/IO expansion, and 1 RS-232 port.
Universal inputs
Universal inputs are the most flexible points on the controller. Each can be configured in Niagara as:
- 0–10 V for pressure transmitters, humidity sensors, CO2 sensors, VSD speed feedback and most "active" sensors
- 4–20 mA for loop-powered transmitters such as pressure, flow and level sensors, common in plant rooms because current signals tolerate long cable runs and electrical noise
- NTC thermistor for passive temperature sensors in rooms, ducts, pipes and outside air. Check the sensor's curve matches the input type configured in the station.
- Monitored input, a digital input with line monitoring so a cut or shorted cable can be distinguished from a genuine open or closed contact. Useful for critical status signals such as fire, freeze and pressurisation alarms.
- Digital input for volt-free contacts
- Pulse input for meters with pulse outputs
Because each UI can take any of these, you can allocate inputs once the final sensor schedule is known rather than fixing them at design stage.
Digital inputs
The six dedicated digital inputs take volt-free contacts and pulse signals. Typical uses:
- run status from current switches or contactor auxiliary contacts
- fault or trip signals from drives and pump sets
- filter differential pressure switches
- door and enclosure contacts
- pulse counting from electricity, gas, water and heat meters
Pulse counting on the controller removes the need for a separate pulse counter module on small metering schemes. Set the pulse value (units per pulse) in the Niagara point to get consumption directly in kWh, m³ or litres.
Digital outputs
The four relay outputs switch up to 5 A at 230 V. Use them for:
- enabling fans, pumps, boilers and chillers via their control circuits
- two-position valves and dampers
- lighting contactors
- alarm beacons and sounders
Relay contacts should drive control circuits or contactor coils, not large motor loads directly. Use an interposing contactor for anything above the rating, and fit suppression on inductive loads to protect the contacts.
Analogue outputs
The eight analogue outputs provide 0–10 V (20 mA maximum) to:
- modulating valve and damper actuators
- variable speed drive speed references
- EC fan speed control
- heat recovery and humidifier control signals
Analogue outputs cannot drive relays directly. Use a digital output, or a relay module with a 0–10 V input, where you need switching.
What 24 points of I/O can control
For many plants 24 points is enough on its own. Typical allocations:
Small constant-volume AHU
| Point | I/O |
|---|---|
| Supply, return and frost temperatures | 3 UI (NTC) |
| Room CO2 | 1 UI (0–10 V) |
| Filter alarm, fan run status, fan trip | 3 DI |
| Fan enable | 1 DO |
| Heating valve, cooling valve, damper, fan speed | 4 AO |
That uses 12 of the 24 points, leaving room for a heat recovery wheel, humidification or metering.
Heating and hot water plant
Boiler enable and status, pump duty/standby with run and fault signals, flow and return temperatures, calorifier temperature, outside air temperature, a mixing valve and a gas meter pulse fit comfortably within the onboard I/O.
Retrofit "front end plus local plant"
On retrofit projects IONA often integrates the existing BMS over BACnet, Modbus or a Trend driver and uses its onboard I/O for a plant item the old system never controlled well, such as a new heat pump, a destratification fan or a domestic hot water loop.
Configuring IONA I/O in Niagara 4
The onboard I/O appears in the station as points under the IONA's I/O network. The workflow will be familiar to anyone who has used Tridium NRIO modules:
- Open the I/O device in Workbench and use the point manager to add the points you need.
- Choose the input or output type for each universal input (voltage, current, thermistor, digital and so on).
- Set the conversion: engineering range for 0–10 V and 4–20 mA, thermistor curve for NTC, units per pulse for meters.
- Add alarm extensions and history extensions as for any other point.
- Link the points into your logic on the wire sheet.
Name and tag points consistently from the start, using the same tags as the rest of the estate, so hierarchies, graphics templates and analytics work without rework.
Licensing and onboard I/O
IONA is licensed by points, in tiers of 100, 250, 500, 1,250, 2,500, 5,000 and 10,000, with upgrades available from 50 points. Each onboard I/O point you use consumes one point of the licence, just like a proxy point from BACnet or Modbus. Plan the licence around onboard I/O plus integrated points plus headroom for future additions. Licence upgrades are available as IONA licence upgrades.
An IONA licensed for fewer than 150 points is classed as a Niagara Edge device, which matters for how it is counted on the supervisor's licence: an Edge-class device uses one tenth of a standard Niagara network connection, so ten small IONAs need only the supervisor connection capacity of a single JACE. See Global Capacity points for how Niagara counts points.
Expanding beyond 24 points: the eBMS/IO bus
When a plant needs more hard-wired points, IONA expands through its dedicated RS-485 eBMS/IO port. Because it is a separate port, expansion modules do not share bandwidth with the BACnet MS/TP or Modbus networks on the general-purpose RS-485 ports.
The eBMS/IO range is a family of DIN-rail Modbus I/O modules, including:
| Module | Points |
|---|---|
| eBMS IO Multi IO | 6 UI, 4 DI, 2 AO, 6 DO |
| eBMS/IO 4DO | 4 relay outputs, 16 A |
| eBMS/IO 12DI 6DOH | 12 DI, 6 relay outputs with hand/off/auto switches |
| eBMS/IO 4AO 3DO | 4 analogue outputs with override, 3 relay outputs |
| eBMS/IO sunblind module | 2 DI, 2 relay outputs, 16 A, for blinds |
Modules with hand/off/auto switches are useful on plant where operators need manual override at the panel. The eBMS/IO CON interface supports up to 31 I/O modules on one RS-485 network, so the expansion bus scales well beyond a single plant room.
Other ways to add I/O
- Third-party BACnet or Modbus I/O modules, such as the iSMA CONTROLLI MIX series, on the general-purpose RS-485 ports or over IP
- LoRaWAN wireless I/O and sensors through the LoRaWAN option, for points that would be costly to cable (see IONA option cards)
- Integrated field controllers over BACnet or Modbus, which bring their own I/O and local control
See BMS I/O modules explained for help choosing.
Sizing I/O: leave spare capacity
Design to about 80% of the available points on day one. Plant changes over its life: a new sensor is requested after handover, a pump set gains a standby, a meter is added for a tenant. A panel designed to 100% means every change needs an extra module and a trip back to the panel builder. With IONA's 24 onboard points plus the eBMS/IO bus, spare capacity is cheap to build in.
Also check the spread across point types, not just the total. A plant with 14 temperature sensors but only six universal inputs needs expansion even though it has fewer than 24 points in total. Universal inputs are the flexible pool, so use the dedicated digital inputs for status signals first and save UIs for analogue sensors.
Building a point schedule for IONA
A point schedule is the single most useful document on any controls project. For an IONA panel, list every point with:
| Column | Example |
|---|---|
| Point name | AHU1_SupplyTemp |
| Description | AHU 1 supply air temperature |
| I/O type and terminal | UI1 |
| Signal | NTC 10k type 3 |
| Range and units | −10 to 50 °C |
| Alarm limits | Low 12 °C, high 30 °C |
| History | 15-minute interval |
| Tags | supply, air, temp, sensor |
Fill it in before panel build. It drives the panel wiring diagram, the Niagara point configuration, the commissioning checklist and the O&M manual, and it lets you check the I/O count and licence size in one place.
Commissioning and troubleshooting onboard I/O
Commission each point end to end: apply a known signal or condition in the field and confirm the right value appears in the station. Common problems and their causes:
Temperature reads far too high or too low. The thermistor curve in Niagara does not match the sensor (for example a 10k type 2 sensor configured as type 3), or the sensor is wired to a voltage-configured input.
A thermistor input reads a fixed extreme value. The cable is open circuit (very cold reading) or short circuit (very hot reading). Check terminations.
A 4–20 mA input reads zero. The loop is not powered, polarity is reversed, or the input is configured as 0–10 V. Measure the loop current with a meter.
A 0–10 V input jumps around. Electrical noise from nearby power cables, or a shared 0 V reference with a poor connection. Use screened cable and check the common.
An actuator does not move on a 0–10 V output. Check the actuator is powered separately, that its control signal is set to 0–10 V rather than 2–10 V or 4–20 mA, and that the output is not in override in the station.
A relay output clicks but the plant does not start. The fault is downstream: check the interposing contactor, the plant's enable circuit and any safety interlocks.
Pulse totals are wrong. The units per pulse value is incorrect, or contact bounce on a mechanical meter output is counting extra pulses.
Wiring good practice
- Keep low-voltage input wiring away from 230 V output and power cabling, and cross at right angles where unavoidable.
- Use screened cable for analogue inputs on long runs and earth the screen at one end only.
- Fuse relay output commons and fit suppression to inductive loads.
- Label every terminal against the point schedule; it saves hours at every future service visit.
- On the RS-485 expansion bus, daisy-chain the modules and terminate the ends (see RS-485 wiring and termination).
Frequently asked questions
How much I/O does the IONA controller have?
24 onboard points: 6 universal inputs, 6 digital inputs, 4 relay digital outputs and 8 analogue outputs.
Can IONA universal inputs read thermistors?
Yes. Each universal input can be set to NTC thermistor, 0–10 V, 4–20 mA, monitored input, digital input or pulse.
What is the relay rating on IONA digital outputs?
Each digital output relay is rated up to 5 A at 230 V. Use interposing contactors for larger loads.
Do onboard I/O points use licence capacity?
Yes. Each onboard I/O point used consumes one point of the IONA's Niagara licence.
How do I add more I/O to an IONA?
Connect eBMS/IO modules to the dedicated RS-485 eBMS/IO port, add BACnet or Modbus I/O modules on the general RS-485 ports, or use LoRaWAN wireless devices through the LoRaWAN option.
Can IONA analogue outputs drive 2–10 V actuators?
Yes. A 2–10 V actuator works on a 0–10 V output; scale the point in Niagara so 0% maps to 2 V. Check the actuator's own configuration matches.
Does a JACE have onboard I/O?
No. JACE controllers have no onboard I/O; all physical points come from remote I/O or field controllers. This is one of the main differences between IONA and JACE.