Installation and wiring

Input modes

The IEC supports two different input modes; High resolution with a narrow scope and Low resolution with a broad scope.

ResolutionScopeResistance RangeP13
HighNarrow30 $\Omega$ $\leq$ R $\leq$ 7.5 k$\Omega$Attached
LowBroad300 $\Omega$ $\leq$ R $\leq$ 43 k$\Omega$Removed

Switching between these two modes is done with a jumper on the I/O board. To move this jumper you first need to detach the ARM CPU board from the I/O board.

Search for a jumper in the middle of the I/O board marked P13. You can find it north (11'o clock) of the S1 / RC connector (P12).

With the jumper attached on P13, the board operates at high resolution with a narrow scope.

By removing the jumper, the board switches to low resolution with a broad scope.

This step is necessary to manage RTD sensors with a resistance (R) of more than 7.5 kOhm.

Place the jumper on a single header pin for safekeeping.

Failover relays

As a safeguard, the IEC has two relays which bridge the S1 port directly to the RC port in case of a fault.

Whenever the power is lost, or there is a failure in communication between the CPU board and the I/O board (for >= 30min), the I/O board automatically switches to this failover state.

In this case, the IEC decouples from the controller and the outdoor temperature sensor is then directly connected to the controller.

This failover can also be activated remotely by NODA.

Shunt resistor

When using a sensor with a resistance ($Rsensor$) of more than 43 kOhm, it is required to use an appropriately sized resistor ($Rshunt$) on P14 to scale down the resistance reported to the IEC ($Riec$).

The sensor is wired to the IEC after the failover relays and in parallel with the shunt resistor. As such, the resistance reported to the IEC can be calculated using the equation for calculating resistors in parallel:

$${1 \over Riec } = { 1 \over Rsensor } + { 1 \over Rshunt } $$

Solving for $Rshunt$, the equation becomes:

$$ Rshunt = { Rsensor * Riec \over Rsensor - Riec } $$

Use the above equation to calculate the value of the shunt resistor where required.

See details in Appendix B for more information and an example.

Supported passive sensors (RTD)

As long as an RTD sensor is within the measurements range of the I/O board and the resolution is adequate, the IEC can support any RTD sensor. However, sensors not listed in this table require implementation effort by NODA.

Type/element$\Omega$ @ -40C$\Omega$ @ +40CResolutionShunt Required
PTC 5224572.301132.64HighNo
NI1000 DIN791.311230.11HighNo
NI1000 L&G830.901185.67HighNo
PT1000 ITS839.671158.45HighNo
PT1000 AMERICAN840.301157.83HighNo
PT1000 IEC842.741155.41HighNo
PT1000 DIN842.751155.39HighNo
NTC AF401152.792231.85HighNo
T1 PTC1840.072638.16HighNo
DRT 34539725.313521.87LowNo
NTC Regin15833.069166.94LowNo
NTC 1000@2523393.14574.49LowNo
NTC TA 1800@2535687.021049.20LowNo
NTC 21C 1800@2539071.871034.67LowNo
NTC EGU43213.451041.67LowNo*
NTC Generic45025.692081.92LowNo*
NTC 21C 5000@25167813.712662.88LowYes
TEU NTC10AN239810.855593.53LowYes
TEU NTC10336515.835323.02LowYes

* Depends on the requirement to read low temperatures.

Supported active sensors (Volt)

Type/elementTyp. V. @ -50CTyp. V. @ +50C

Output modes

The IEC supports two different output modes;

  • Voltage (standard for passive and active sensors)
  • Transistor (only for passive sensors)

Voltage mode is the preferred mode and is used to simulate both passive and active sensors. If calibration towards the controller fails, you may need to switch to transistor mode.

Changing from a voltage to transistor mode

For changing the output mode, three jumpers need to move on the I/O board:

  • P9 (marked as 2 in the figure)
  • P10
  • P11 (marked as 1 in the figure)

Headers and jumpers

ModeP9P10, P11Sensor type
VoltageJumperJumperPassive and active

Connecting to the outdoor sensor and controller

Before any wiring takes place, it is essential to know if the outdoor sensor is a passive or an active sensor.

If it is a passive sensor (RTD), then there are no special polarity requirements. However, if it's an active sensor, then the polarity must be respected. I.e. it must be wired from plus to plus and from minus (GND) to minus.

Wiring diagram

Outdoor sensor wiring

RTD Sensors

When connecting a passive outdoor temperature sensor to the S1 port of the IEC, no particular attention to the polarity is necessary.

Wiring from the IEC RC port to the controller requires the polarity of the I/O board to match the polarity of the Analog Input (AI) port of the controller.

If this is not marked, then use a multimeter while the outdoor temperature sensor is still attached to the controller and identify the polarity. If wired incorrectly; the controller, the IEC or both might take damage.

PT1000 sensor wiring

0-10V Sensors

When connecting an active outdoor temperature sensor to the IEC, make sure that the polarity matches the screw terminal. If wired incorrectly the IEC might take damage.

Wiring from the IEC RC port to the controller requires the polarity of the I/O board to match the polarity of the Analog Input (AI) port of the controller.

If this is not marked, then use a multimeter while the outdoor temperature sensor is still attached to the controller and identify the polarity. If wired incorrectly; the controller, the IEC or both might take damage.

0-10V sensor wiring

0-10V Controller AO

This variant is a situation where the controller can supply an Analog Output (AO) with a 0-10V signal that corresponds to the outdoor temperature sensor measurement.

The outdoor temperature sensor connects directly to the controller, or via a bus and does not connect to the IEC.

In this case, the controller's AO port communicates the outdoor temperature as a 0-10V signal to the IEC's S1 port.

The IEC reads port S1, performs it's computations and writes a 0-10V signal (using the same temperature span as defined for the input sensor) on its RC port. This signal represents the new outdoor temperature.

Make sure to match the polarity on both sides. If wired incorrectly; the controller, the IEC or both might take damage.

0-10V Controller AO wiring

This scenario often requires a one-time re-programming of the controller.

1-Wire Sensors

1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed data, signalling, and power over a single conductor.

The IEC supports up to 8 devices on a bus.

Temperature probes

The IEC is compatible with any DS18S20 or DS18B20 sensor. The ones supplied are wired to the screw terminal on the I/O board as follows:

Thermokon VFG54+3 (BROWN)2 (GREEN)1 (WHITE)


It is possible the generalise any bus into three different topologies:

  • Linear topology: One main 1-Wire bus with insignificant (less than 3m) branches or stubs.
  • Stubbed topology: One main 1-Wire bus with significant (more than 3m) branches or stubs.
  • Star topology. The main 1-Wire bus splits into multiple branches.

It is highly recommended to keep to either a linear topology or a stubbed topology.

Example 1-Wire circuit diagram

Network (Bus) length

The radius of a network is the wire distance from the IEC to the most remote device. This length S measures in meters. The network weight is the total amount of connected wire in the network, and also measures in meters.

For example, a star network configuration with three branches of 10m, 20m, and 30m would have a radius of 30m (i.e., the distance from 1-Wire master to the furthest slave) and weight of 60m (i.e., the total length of wire in the network, 10m + 20m + 30m).

The total weight of the network should not exceed 100 meters to prevent communication issues.

Cable recommendation

It is highly recommended to use a UTP cat 5 cable as this type of cable is readily available and has been proven reliable.

RS232 optical probe (IEC 62056-21)

The optical probe comes with 2m of cable. If additional length is required, then use a low capacitance (UTP cat 5) cable for a maximum combined length of 50 meters.



RS232 optical probe wiring

Supported protocols over the optical probe

  • M-Bus
  • KMP (Kamstrup 4XX, 6XX, 8XX)
  • IEC 61107

Wired M-Bus

Wired M-Bus support for a single slave comes via an add-on board. This board (KOMM2) does not come as standard.

The KOMM2 board is designed to work with a single slave device and does not work in a network with several slave devices.

The M-Bus uses two-wire cables which are going from the M-Bus Master / Repeater to each M-Bus device (bus structure). The M-Bus is polarity independent and does not require line termination resistors.

The max cable length depends on the type of cable used. Using a low capacitance cable a length of >100 meters is possible.

Connection to the KOMM2 board

Since the M-Bus is polarity independent, no special care is required when connecting the cable from the equipment to the KOMM2 board.

If the port on the M-Bus slave is occupied, an M-Bus splitter is required. The splitter is a device which allows multiple masters to communicate with the same network of M-Bus slaves.

Connecting to the RUT

  1. Placed the RUT in a spot where it can connect to the mobile network.

  2. Connect the power.

  3. Connect the IEC to the RUT by connecting an ethernet cable from the ethernet port of the IEC to either of the three ethernet ports marked LAN1, LAN2, LAN3 on the RUT router.

Note: The IEC will not connect to the internet unless the RUT has a working mobile connection.