Modbus RTU Module (A)
Description
This is an industrial-grade data acquisition and control module with an RS485 interface. It supports 2 relay outputs, 2 digital inputs, 2 analog current outputs, and 2 analog inputs. It uses the Modbus RTU protocol and features built-in protective circuits such as power isolation, magnetic coupling isolation, self-resetting fuses, and TVS.
| SKU | Product |
|---|---|
| 34740 | Modbus RTU Module (A) |
Electrical Safety and Relay Precautions
- This product must be used by professional electricians or technical personnel. Please take appropriate electrical safety, leakage prevention, and insulation measures during use.
- Before installing, maintaining, or replacing relay equipment, be sure to turn off the power and unplug the connector.
- Do not attempt to disassemble the relay equipment to avoid damage or electric shock.
- Install and place the relay product properly. Do not use it in humid, overheated, flammable, or explosive environments to avoid safety accidents caused by improper installation or use.
1. Load Matching
-
Ensure that the rated voltage and current of the relay match the load. Do not overload. Excessive current may cause contact melting, sticking, or even fire.
-
For inductive loads (motors, coils, lamps, etc.), the inrush current may be much higher than the rated current. Select a relay with sufficient margin for the rated current.
2. Short Circuit and Overcurrent Protection
-
Add a fuse or circuit breaker to the relay circuit to prevent relay burnout due to load short circuit or accidental overcurrent.
-
Ensure no short circuit in the load circuit during wiring, and use protection components with appropriate current ratings if necessary.
3. Arc and Contact Protection
-
Arcing occurs at the moment of relay switching, which can easily cause contact wear or welding.
-
It is recommended to use arc suppression circuits such as RC snubbers or varistors for inductive loads.
4. Installation Environment
-
Avoid using in humid, high-temperature, flammable, explosive, or dusty environments.
-
Mount the relay securely to prevent false operation or damage due to vibration or impact.
5. Power Off Operation
-
Before maintenance, wiring, or relay replacement, be sure to disconnect power to ensure personal and equipment safety.
-
Latching relays are energized only when changing state and are normally de-energized. Avoid strong vibration or magnetic field interference that could alter the relay state.
6. State Confirmation
-
After powering on, confirm or reset the relay state as needed to avoid abnormal operation due to transportation, installation, or external interference.
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Avoid cutting power during latching relay operation to prevent undefined states or contact damage.
7. Regular Inspection
-
After long-term use, regularly inspect the relay contacts, terminals, and insulation to ensure normal operation.
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If abnormal heating, odor, or burn marks appear, immediately disconnect power and replace the relay.
Specifications
Communication Parameters
| Parameter | Specification |
|---|---|
| Supply Voltage | 7 V ~ 36 V |
| Communication Interface | RS485 |
| Baud Rate | 2400, 4800, 9600, 19200, 38400, 57600, 115200, 128000, 256000 |
| Default Communication Format | 9600, N, 8, 1 |
| Modbus Protocol | Standard Modbus RTU Protocol |
| RS485 Address Range | 1 ~ 255 |
| Indicator LEDs | STA: MCU status, flashes when MCU is working normally TXD: Transmit indicator, lights when sending data RXD: Receive indicator, lights when receiving data |
Input/Output Parameters
| Parameter | Specification |
|---|---|
| Relay Output | 2 DO, 1 normally open + 1 normally closed, ≤10 A 250 V AC or ≤10 A 30 V DC |
| Digital Input | 2 DI, 5 V ~ 36 V, dry contact / wet contact (NPN or PNP), built-in bidirectional optocoupler |
| Analog Output | 2 AO, 0 ~ 20 mA, 12-bit resolution, 1 μA, accuracy ±0.03 mA |
| Analog Input | 2 AI, 0 ~ 10 V / 2 ~ 10 V / 0 ~ 20 mA / 4 ~ 20 mA, 12-bit resolution, accuracy ≤3‰, update rate 31 Hz, sampling resistor 249 Ω |
Relay Output
| Parameter | Specification |
|---|---|
| Number of Relays | 2 |
| Contact Type | 1 normally open + 1 normally closed |
| Contact Load | ≤10 A 250 V AC or ≤10 A 30 V DC |
Analog Output
| Parameter | Specification |
|---|---|
| Output Mode | 2 current outputs |
| Resolution | 12 bits, 1 μA |
| Range | 0 ~ 20 mA |
| Output Accuracy | ±0.03 mA |
Digital Input
| Parameter | Specification |
|---|---|
| Number of Inputs | 2 |
| Wet Contact Range | 5 V ~ 36 V DC |
| Input Type | Dry contact / wet contact (NPN or PNP) |
| Isolation Type | Bidirectional optocoupler |
Analog Input
| Parameter | Specification |
|---|---|
| Number of Inputs | 2 |
| Range | 0 ~ 10 V / 2 ~ 10 V 0 ~ 20 mA / 4 ~ 20 mA |
| Sampling Accuracy | 12-bit resolution, accuracy ≤3‰ |
| Data Update Rate | 31 Hz |
| Current Sampling Resistor | 249 Ω |
Basic Functions
Supports digital and analog input/output via RS485 sending Modbus RTU protocol commands.
Hardware Description
Hardware Terminal Description
Product Wiring Table
Relay Output
| Terminal Label | Function |
|---|---|
| CH1 NC | Relay CH1 normally closed contact |
| CH1 COM | Relay CH1 common terminal |
| CH1 NO | Relay CH1 normally open contact |
| CH2 NC | Relay CH2 normally closed contact |
| CH2 COM | Relay CH2 common terminal |
| CH2 NO | Relay CH2 normally open contact |
Analog Input/Output
| Terminal Label | Function |
|---|---|
| AO1 | Analog output channel 1 |
| AO2 | Analog output channel 2 |
| AGND | Analog ground |
| AI1+ | Analog input channel 1 positive terminal |
| AI1- | Analog input channel 1 negative terminal |
| AI2+ | Analog input channel 2 positive terminal |
| AI2- | Analog input channel 2 negative terminal |
Communication and Power Supply
| Terminal Label | Function |
|---|---|
| 485 A+ | RS485 signal line A+ |
| 485 B- | RS485 signal line B- |
| EARTH | RS485 shield ground |
| DC 7 ~ 36 V + | Power supply positive |
| DC 7 ~ 36 V - | Power supply negative |
| ⊙ DC 7 ~ 36 V | Round DC power connector |
The round DC power connector and the screw terminal power input must not be connected simultaneously. Doing so may damage the power supply or the module, or cause other safety risks.
Digital Input
| Terminal Label | Function |
|---|---|
| DI COM | Digital input common terminal |
| DGND | Digital ground |
| DI1 | Digital input channel 1 |
| DI2 | Digital input channel 2 |
DI COM Terminal
↑ DI COM is the common terminal for input signals. It can be left unconnected, connected to power positive, or power negative. It can be powered directly from the supply voltage or from an independent power source.
Three connection methods:
- Unconnected (floating): dry contact input
- Connected to power positive: active low trigger, NPN-type wet contact input, voltage 5V-36V DC
- Connected to power negative: active high trigger, PNP-type wet contact input, voltage 5V-36V DC
Digital Input Wiring
The digital input wiring types: passive dry contact input, active wet contact NPN input, active wet contact PNP input.
Dry Contact Input Wiring Diagram
Active Wet Contact NPN Input Wiring Diagram
Active Wet Contact PNP Input Wiring Diagram
Relay Output Wiring
Normally Open Relay Output Wiring Diagram
Connect the live wire (for AC loads) or power positive (for DC loads) to the COM terminal, then connect from the normally open (NO) terminal to the load.
Analog Input Wiring
When opening the device enclosure, you will find jumpers near the device terminals, corresponding to channels AI1~AI2. The jumper mode must be selected according to the measured signal, otherwise measurement data will be inaccurate.
- For voltage signal measurement, disconnect the jumper for the corresponding channel.
- For current signal measurement, connect (short) the jumper for the corresponding channel.
AI+ is the positive input terminal, AI- is the negative input terminal.
For current measurement, current flows into AI+ and out of AI-; for voltage measurement, connect voltage positive to AI+ and voltage negative to AI-.
Current Output Wiring
Connect AO to the load positive terminal and AGND to the load negative terminal.
Power and Communication Connection
Connect the USB TO 485 converter to the target board using jumper wires, connecting A-->A and B-->B as shown in the figure below:
