WB-MRWM2

Purpose

WB-MRWM2 is designed for:

• switching high-power electrical loads up to 20 A, including inductive loads;
• measuring the root mean square (RMS) voltage;
• measuring active power;
• disconnecting the load when the voltage exceeds the permitted range; the limits are configured separately for each output.

The device also provides configurable:

• protective startup delays;
• restart delays;
• timer functions.

Delays and timers are configured separately for each output.

Two digital inputs provide direct control of the outputs.

The device requires a 9…28 V low-voltage power supply.

For relay selection, see Relay selection recommendations.

Technical specifications

Operating principle

Indicators

The module has 4 indicators:

• Status — green. Indicates Modbus communication: lights up when low-voltage power is applied, flashes during polling over RS-485, and flashes rapidly during a firmware upload;
• Relay — orange. Indicates the relay state; lights up when the relay contacts are closed;
• Power — orange. Flashes at a rate proportional to the power consumption. At 4.5 kW, it appears continuously lit;
• Phase fail — orange. Lights up when the voltage is outside the permitted range (configurable; default: 207…242 V).

Inputs

Inputs use numbered removable terminal blocks with a common iGND terminal and operate as dry-contact inputs.

Connect switches for direct output control, or a signal source for pulse counting and frequency measurement.

Both maintained and push buttones are supported. Push buttones support several press types, each of which can be assigned an action for scene control. Press events are also transmitted to the controller over Modbus for processing in software.

The Wiren Board controller does not poll press counters by default. Enable their polling in the device settings if required.

By default, each input controls the output with the same number. Input mode is Latching switch — the relay contacts follow the switch contacts. Change the switch type and input parameters in the settings.

Press-type recognition

The module recognises four press types: short; long; double; and short followed by long.

Presses can be processed on the controller, which receives a separate counter for each type over Modbus, or locally in the module to control its outputs.

Press-recognition parameters can be changed in the settings.

Outputs

The module has 2 independent normally open relay outputs.

The relays are certified for AC use only; their DC load capacity may be lower. For permitted load power and types, see Relay selection recommendations.

Power and voltage measurement

Each WB-MRWM2 output has a measurement circuit that measures:

• the root mean square (RMS) voltage;
• active power, measured correctly for capacitive, inductive and nonlinear loads.

The power reading update rate in the Modbus registers depends on the load power. It is lowest at low loads, when readings update once per second.

Different outputs of the device can be connected to different phases of a three-phase supply.

Delays

Protection Startup Delay (s) starts:

• when the device firmware starts (approximately 2.5 s after low-voltage power is applied);
• when the voltage returns to normal after voltage monitoring has blocked the output.

The delay reduces inrush currents by staggering the startup of loads.

Restart Delay After Output Turn Off (s) starts when the relay switches off. It protects loads sensitive to frequent switching, such as compressors and pumps.

Delays are configured separately for each relay output.

Output timer functions

Timer functions switch module outputs on or off according to a defined timing sequence.

Direct control and timer functions can be used in the same module. Each output can have only one timer function. Outputs are configured independently; changing one output does not affect the others. More about relay module timer functions.

Each relay output supports these timer functions: On-delay, Off-delay, Switch on for a time, Switch on for a time (with command reset), Switch off for a time, Switch off for a time (with command reset), ON/OFF cycle.

Configuring output timers.

Voltage monitoring

This function is enabled separately for each output. The following settings are also configured individually: Overvoltage Threshold (V), Undervoltage Threshold (V) and Voltage Dip Duration (s).

If the measured output voltage exceeds the Overvoltage Threshold (V) or falls below 120 V, the output is blocked (switched off) immediately.

If the measured output voltage is above 120 V but below the Undervoltage Threshold (V) for longer than the Voltage Dip Duration (s), the output is blocked.

Blocking is released when the voltage returns within the permitted limits, allowing for the fixed hysteresis.

While blocked, the device accepts relay commands over Modbus and from inputs in Latching switch, Turn off all outputs and mapping-matrix modes. The last command is executed when blocking is released.

Safety Mode

Safety Mode allows processes to stop if control of the module is lost, for example because the RS-485 cable is damaged. Account for possible loss of communication with the controller when designing control systems. See Configuring Safety Mode.

Installation

Mount the device on a standard 35 mm DIN rail. The V+ GND A B terminal block, with a 3.5 mm pitch, connects the power supply and RS-485 communication bus. Correct bus wiring is essential for reliable communication; see RS-485 bus wiring and connection.

If devices on the RS-485 bus use different power supplies, their GND terminals must be interconnected. See Grounding Wiren Board devices and connecting GND and iGND.

Use flexible stranded wire with insulated wire-end ferrules (NSHVI).

Strip the insulation to the sleeve length, or strip a little more and trim the protruding wire after crimping. Use a ferrule crimping tool. A crimped ferrule protects the strands from the screw clamp and secures the connection.

Do not overtighten the terminal screws: excessive force damages the screw terminal.

Relay switching briefly increases power consumption (see specifications). Choose a supply with adequate power reserve. For long supply cables, allow for the voltage drop along the cable.

Digital inputs activate when connected to iGND. The current is low (~2 mA), so any suitable button or switch type can be used. Cable length and cross-section are not critical for contact detection. To reduce interference from nearby power wiring, use twisted pair and connect iGND to the second conductor of the pair. More about connecting iGND/GND terminals.

The wire cross-section at relay output screw terminals must suit the switched load. The screw terminals accept wire cross-sections of 2.5–4 mm².

Install the relay module in accordance with electrical safety requirements and prevent accidental contact with live high-voltage terminals. Operate it under the specified environmental conditions.

Installation example

The figure shows one way to connect loads to WB-MRWM2 WB-MRWM2 installation example.

In this example, wiring upstream and downstream of the relay is protected by a 16 A circuit breaker. Select its rating according to the wire cross-section and the module's maximum switching current.

The diagram shows a water heater and an electric motor connected to outputs K1 and K2.

In this example, outputs K1 and K2 can be controlled both by switches and over RS-485. Input assignments can be changed using the mapping matrix.

For switch types and other module settings, see Configuration.

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  WB-MRWM2 installation example
• 
  Using WB-MRWM2 with two RCBOs

Configuration

Configuration methods

1. Set the parameters in the Wiren Board controller web interface under Settings → Configs → Serial devices driver configuration. If these items are unavailable, check your access level.
2. Write settings to the Modbus registers of the module from the controller console using the utility modbus-utils-rpc or modbus­_client.
3. Without a Wiren Board controller, use the Wiren Board device web configurator or other software; see Using Wiren Board Modbus devices without a controller. You will need a computer with an interface converter: USB-RS485.

Our devices are continually improved. If settings described in this manual are missing, update the device firmware and controller software.

Input closure and press counters

The counters for input closures to ground are Input X counter. These counters are available in all modes for counting pulses and processing dry-contact signals.

When operating with the mapping matrix the following press-type counters are available:

• Single Press Counter — single short presses,
• Long Press Counter — long presses,
• Double Press Counter — double short presses,
• Shortlong Press Counter — short-then-long presses.

These count recognised press types, rather than input closures, and are intended for push-button processing. To use press types in wb-rules enable polling of the corresponding channels.

The counters Counter and Single Press Counter serve similar purposes but process contact closures differently:

• counter Counter increments as soon as the input closure is accepted after the configured debounce time;
• counter Single Press Counter increments when a short press has been detected without a second press. The response time is the short-press duration plus the second press waiting time.

Therefore, when using Single Press Counter to count digital signals, you may need to reduce the second press waiting time. For pulses and reed-switch activations, use Input Counter; use the button press counters when working with push buttons.

All counter values are stored in the relay microcontroller's RAM and reset when power is removed.

Control from switches

The parameter Operating mode lets you select the connected switch type, disable press actions, or select a mode based on the mapping matrix.

In matrix modes, input states and event counters can still be sent to the controller with input actions disabled, depending on channel polling settings.

Matrix modes are universal; switch modes are retained for compatibility with older projects.

When you select the mode Button mapping matrices lets you assign output actions to each of the four press types for scene control and multi-location switching. See Press-type recognition.

Available settings:

• Long Press Time (ms) — distinguishes long and short presses. A press lasting longer than this value is long; otherwise it is short.
• Second Press Waiting Time (ms) — opens a time window after a short press ends. A second press within this window is treated as a double press; otherwise the first press is treated as a single press.
• Debounce Time (ms) — the time for which the input signal must remain unchanged before it is registered and processed by the press recognition algorithm. For press recognition, set this to one-fifth to one-tenth of the second-press waiting time.
• Polling interval for each counter — leave this at the default value; the driver manages polling automatically.

Double-press recognition delays single-press recognition. With the default setting of 300 ms, a short-press event occurs 300 ms after the button is released. If double presses and short-then-long presses are not required, set Second press waiting time to 0 ms. The short-press event will then occur immediately after button release.

Press recognition takes place after debouncing. With Debounce time set to the default 50 ms, presses shorter than 50 ms are ignored. Button release is also registered 50 ms after physical release. Choose the debounce time for the particular button to minimise latency while preventing false events, such as a double press being detected instead of a single press.

Default input settings:

• each input controls the corresponding relay: for example, input 2 controls relay 2;
• input mode — latching switch.

Useful resources:

• Example of processing press counters in wb-rules.

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  Selecting the mode for relay input 1
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  Assigning actions to press types
• 
  Configuring polling of channel L1

Debouncing

For any relay input, configure debouncing with the parameter Debounce Time (ms). Range: 0–2000 ms; default: 50 ms.

Output states at power-on

The following power-on behaviours are available:

• Set output to fail-safe state (default) — after power-on, outputs follow the setting Fail-safe output state;
• Restore last state — saves the last output states and restores them at power-on;
• Set according to input states — after power-on, outputs follow the input states (input N closed → output N on, where N is the input/output number). This only works with inputs in Latching switch mode.

Safety Mode

Safety Mode can stop a process if control of the module is lost, for example because the RS-485 cable is severed. Account for communication loss when designing control systems.

The fail-safe timer restarts after every successfully received and processed Modbus. When the configured time expires, the relay enters Safety Mode. Normal operation resumes when communication is restored. The default timeout is 10 seconds.

Each output has a configurable fail-safe state and can be configured to enter it on communication loss.

Input control behaviour can be configured:

• Do not block — previously enabled input control remains enabled.
• Block in safe mode — inputs cannot control the relays.
• Allow only in safe mode — input control blocked in normal operation becomes available in safe mode.

Configuring frequency measurement

To measure the frequency of a signal at an input, configure that input as follows:

1. Select the operating mode Control disabled, input measures frequency. This disconnects the input from output control.
2. Set Debounce time to 0 ms to measure the highest supported frequencies. For low-frequency signals, the debounce time may instead be set below the pulse period.
3. Disable polling of the input to reduce bus traffic.

For details of frequency register updates, see Updating frequency values in registers.

Protective Functions

Delays

For each relay output, you can configure the Protection Startup Delay (s) and Restart Delay After Output Turn Off (s). Available range: 0…999 s; default: 0 s.

Voltage monitoring

Voltage monitoring settings are configured separately for each relay output:

• enable voltage blocking (enabled or disabled; disabled by default);
• lower voltage limit (120…220 V; default: 207 V);
• upper voltage limit (230…277 V; default: 242 V);
• permitted voltage dip duration (0.5…10 s; default: 5 s).

Configuring output timers

In the device settings, open Timers, select a function and configure its duration for the corresponding relay output.

Wiren Board controller web interface

Selecting a template

To display the device on the Devices tab of the Wiren Board controller web interface, add it automatically by scanning for Wiren Board devices on RS-485 or manually by selecting the template WB-MRWM2.

Controlling the device and viewing values

The web interface allows you to control device outputs and view readings. To change the displayed channels, edit the device configuration in the wb-mqtt-serial driver settings.

Measured values and controls:

• Input x — state of input x;
• Input x counter — closure counter for input x;
• Command Kx — command for output Kx;
• Real State Kx — actual state of output Kx;
• Urms Lx — RMS voltage of phase Lx, V;
• AP energy Lx — forward active energy for phase Lx, kWh;
• P Lx — forward active power for phase Lx, W;
• Voltage Status Kx — voltage monitoring status for phase Lx;
• Blocking Kx — blocking status of output Kx;
• Protection Startup Delay Kx — protective startup delay timer for output Kx;
• Restart Delay Kx — restart delay timer for output Kx.

Modbus operation

Wiren Board devices use Modbus RTU. The physical connection uses the RS-485.

interface. All main commands for reading and writing one or multiple registers are supported. See the list in the Modbus protocol description.

The module can be configured:

• in the Wiren Board controller web interface;
• using the Wiren Board device web configurator;
• using third-party software.

Default port settings

In current firmware, setting Stop bits is optional: the device also operates correctly when its number of stop bits differs from the Modbus master setting.

For a faster response, we recommend increasing the baud rate to 115200 bit/s; see Communication parameter settings.

Modbus address

Each device on the bus must have a unique address from 1 to 247. The factory-assigned address is printed on labels on the enclosure (top cover, side or underside). Devices in a production batch are assigned different addresses, so devices in one order will usually have different addresses.

For instructions on finding, changing or resetting the address, see Wiren Board device Modbus address.

Fast Modbus extension

Fast Modbus extends standard Modbus with rapid discovery of Wiren Board devices on RS-485 and event polling.

These features are enabled by a special command from the master, so Wiren Board devices remain compatible with third-party equipment.

Not every register supports event generation. Check the register map: event-capable registers are marked with ⚡. See Fast Modbus.

Modbus register map

Firmware updates and resetting settings

Wiren Board devices support firmware updates over Modbus. This allows bugs to be fixed at the installation site and, where technically possible, new features to be added. Settings stored in the device are retained during a firmware update.

Instructions:

• Firmware update ()
• Resetting settings
• Connection parameter settings
• Modbus address: find, reset or change
• Updating the bootloader

New firmware releases are listed in the device firmware changelog.

Known issues

ERRMRWM0001 — Energy accumulation is unavailable in firmware 1.19.0 through 1.20.1 inclusive; the energy register remains at 0. Update to firmware 1.20.2 or later.

ERRMR17 — Hardware batches v1.4B–v1.5C may consume more power and run warmer with relays on. This was corrected in batch v1.5D. A 12 V supply reduces heating where suitable; contact support if the module becomes unusually hot.

Hardware revisions

Troubleshooting

Interference from relays and contactors

Relays and contactors can interfere with nearby devices. When switching loads, especially inductive loads, the contacts generate high-frequency transients with amplitudes of several kilovolts, which may couple into other circuits. Snubber networks suppress these transients, reducing interference and improving equipment stability. See Interference when switching inductive loads

Images and drawings

1. Enclosures, circuit breakers, contactors and other third-party symbols.

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  Overall dimensions: 53.3 × 90.2 × 57.5 mm (L × W × H)

Images and diagrams for earlier hardware versions

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  WB-MRWM2 relay module before version v1.7
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  WB-MRWM2 circuit board before version v1.7
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  WB-MRWM2 installation example before version v1.7