WitMotion WT901C(RS485) Inclinometer Sensor User Manual

Introduction

The WT901C is a multi-sensor device designed for detecting acceleration, angular velocity, angle, and magnetic field. Its compact size makes it suitable for industrial applications such as condition monitoring and predictive maintenance. By interpreting sensor data with smart algorithms, the device can be configured for a wide range of use cases.

The WT901C is scientifically known as an AHRS IMU sensor, capable of measuring 3-axis angle, angular velocity, acceleration, and magnetic field. Its primary strength lies in its algorithm for accurately calculating three-axis angles, making it ideal for applications requiring high measurement accuracy.

Key Advantages:

• Heated for best data availability: Features a new WITMOTION patented zero-bias automatic detection calibration algorithm that outperforms traditional accelerometer sensors.
• High precision output: Provides Roll, Pitch, Yaw (X, Y, Z axis) data for Acceleration, Angular Velocity, Angle, and Magnetic Field.
• Low cost of ownership: Offers remote diagnostics and lifetime technical support from the WITMOTION service team.
• Comprehensive support: Includes developed tutorials, manuals, datasheets, demo videos, free Windows software, and communication protocols for project development.

WITMOTION sensors are recognized by thousands of engineers as a reliable solution for attitude measurement.

Warning Statement

• Applying more than 5 Volts across the sensor wiring can cause permanent damage.
• Connecting VCC directly to GND will burn the circuit board.
• For proper instrument grounding, use WITMOTION with its original factory-made cable or accessories.
• For secondary development projects or integration, use WITMOTION with its compiled sample code.

Software Instructions

To enhance user experience and customer service, a new version of PC software has been developed. The software and universal instructions can be downloaded via the following link:

WITMOTION New Software (Universal) Download

The 2022 old version software will remain available. Refer to "Chapter 3 Use Instructions with PC" for details.

Use Instructions with PC

Connection Method

The PC software is compatible only with the Windows operating system.

WT901C RS485 Playlist

Serial Connection

Step 1: Connect the sensor with a serial converter.

PIN Connection:

• VCC - 5-36V
• B - B
• A - A
• GND - GND

(VCC 5-36V is recommended for connection)

Recommended Tools:

The following tools are recommended for connection:

• 3-in-1 converter
• 6-in-1 converter
• RS485 serial cable

Link to tutorial of 3-in-1 serial converter/ RS485 serial cable (CH340 driver)

Link to tutorial of 6-in-1 serial converter (CP2102 driver)

Step 1: Connect the sensor using the provided dupont line or RS485 line.

Step 2: Unzip the software and install the CH340 driver.

Driver Download Link

How to Install and update the CH340 driver: Click the "Uninstall" button first, then click on the "Install" button.

How to verify your driver is working:

1. To check if the CH340 enumerates to a COM port, open the Device Manager. You can click the Start button (or Windows icon) and type "device manager" to search for it.

   Diagram Description: A screenshot of the Windows Control Panel showing "Device Manager" highlighted under "Devices and Printers".

2. After opening Device Manager, expand the "Ports (COM & LPT)" tree. The CH340 should appear as "USB-SERIAL CH340 (COM##)". The COM port number may vary depending on your computer.

   Diagram Description: A screenshot of the Windows Device Manager showing the "Ports (COM & LPT)" tree expanded, with "USB-SERIAL CH340 (COM3)" listed.

Step 3: Open the software (Minimu.exe).

Data will appear after auto-search finishes.

Notice: If the auto-search is unsuccessful, please operate manually. Choose the correct COM port and set the baud rate to 9600. Data will then be displayed on the software.

Main Menu

Menu of Configuration

Menu of System

Instruction Start-up: This function prevents data sent by the module from conflicting with the mouse cursor after connecting to the computer. It takes effect on the next module use or power-on.

Menu of Calibrate

Menu of Range

Menu of Communication

Calibration

Preparation: Ensure the sensor is "Online".

Calibration must be performed on the PC software for first-time usage.

Accelerometer Calibration

Purpose: To remove the zero bias of the accelerometer. Uncalibrated sensors may have bias errors, affecting measurement accuracy.

Methods:

1. Keep the module horizontally stationary.
2. Click the "Accelerometer calibration" button.
3. Click "Start calibration" and wait for 3 seconds.
4. Click "Complete Calibration".

Step 5: Judge the result by confirming if there is approximately 1g of gravitational acceleration on the Z-axis when the module is horizontal. The X and Y axis angles should be around 0° after calibration.

Magnetic Field Calibration

Purpose: To remove the zero bias of the magnetic field sensor, which can cause significant measurement errors and affect heading angle accuracy.

Preparation: Keep sensors at least 20cm away from magnetic and iron materials.

Methods:

1. Open the "Config" menu.
2. Click the "Magnetic Field" calibration button and then click "Start calibration".

Step 3: Slowly rotate the module 360° around the X, Y, and Z axes.

Step 4: After rotation, click "End calibration".

Successful result: Most data dots should be within the ellipse. If not successful, move away from potential sources of magnetic field interference.

Gyroscope Automatic Calibration

The gyroscope calibration automatically calibrates the angular velocity. It is recommended to keep this feature active unless the module rotates at a constant speed.

Reset Z-axis Angle

Note: To mitigate magnetic interference, switch to the "6-axis" algorithm and use the "Reset Z-axis angle" function.

The Z-axis angle is an absolute angle, with the northeast sky as the coordinate system, not relative to 0 degree. Resetting the Z-axis to 0 makes the initial angle relative 0. If the Z-axis drifts significantly during use, it can be recalibrated. Upon power-on, the Z-axis will automatically return to 0.

Calibration Method: Keep the module static, click "Config", open the configuration bar, and then click "Reset Z-axis Angle". The Z-axis angle should return to 0 degrees in the module data bar.

Reset Height to 0

This function is only available for modules with a built-in barometer (e.g., WT901B, HWT901B, WTGAHRS1, WTGAHRS2).

Configuration

Baud Rate

The module supports multiple baud rates, with 9600 as the default. To set a new baud rate, select it from the communication rate drop-down box in the configuration bar, ensuring correct connection between the software and the module.

After changing the baud rate, the module will only output data at the new rate. You must select the new baud rate in the PC software to receive data.

Standby and Wake Up

• Sleep: The module pauses operation and enters standby mode, reducing power consumption.
• Wake Up: The module returns to the working state from standby.

The module defaults to a working state. To enter sleep mode, navigate to "Config" in the software and click "Sleep". Click "Sleep" again to release from sleep mode.

Placement Direction

The default installation direction is horizontal. For vertical installation, follow these steps:

1. Rotate the module 90 degrees around the X-axis.
2. Place the sensor 90 degrees vertically.
3. Click "Vertical" under "Install Direction" in the "Config" menu.

Data Recording

Method:

1. Click "Record" and then "Begin".
2. Click "Stop".

Data Playback

This function allows playback of recorded data. A BIN file is created in the "recordFile" folder of the installed software path when recording.

Recorded data playback method:

1. Disconnect the sensor.
2. Click the "File" button, then click "Load".
3. Choose the original path of the software installation and load the BIN file.
4. Click "Run". The binary file will playback, and the rate can be edited during playback.

Bandwidth

The default bandwidth is 20Hz.

Function:

1. A higher bandwidth setting leads to more fluctuation in the data waveform. Conversely, a lower bandwidth results in smoother data. For example, with a 20Hz bandwidth and 10Hz output rate, the waveform is very steady.
2. Increasing the bandwidth can help solve data-repeating issues. For instance, a 20Hz bandwidth with a 100Hz retrieval rate might result in 5 repeating data points. To avoid repeating data, the bandwidth should be set higher than 100Hz.

Restore Factory Setting

Operation method: Connect the WT901C module to the computer via USB-RS485. Click the "Setting" tab and then "Restore Default". After restoring, power cycle the module. Note: This method requires knowing the module's baud rate in advance; if it doesn't match, the instruction may not take effect. Use the short-circuit method for recovery if needed.

6-axis/ 9-axis Algorithm

6-axis algorithm: Z-axis angle is calculated primarily from angular velocity integration, which can lead to calculation errors.

9-axis algorithm: Z-axis angle is calculated and analyzed based on the magnetic field, resulting in minimal drift.

The WT901C defaults to the 9-axis algorithm. If magnetic field interference is present in the environment, switching to the 6-axis algorithm is recommended.

Method:

1. Switch to the "6-axis" algorithm in the "Config" menu.
2. Perform "Accelerometer calibration" and "Reset Z-axis angle" calibration.

After calibration, the device can be used normally.

Set MODBUS Address

The default MODBUS address is 0x50 and can be changed via the software. Enter the new hexadecimal address in the MODBUS address configuration tab and click "change".

After changing the MODBUS address, it may not take effect immediately. The device address needs to be searched again for the change to be recognized.

Multiple Module Cascades

Multiple modules can be cascaded to view data from several devices simultaneously on the PC software.

Tips:

1. Before cascading, change each module's MODBUS address individually using the PC software.
2. Decrease the baud rate to a lower level if the BUS cable is too long, to prevent data packet loss.

Warning Statement:

1. Ensure each sensor is powered with sufficient input voltage.
2. Working voltage requires 3.3-5V input.

Hardware Connection Diagram

Note: When cascading multiple modules, carefully check the wiring between modules: VCC-VCC, A-A, B-B, GND-GND.

Software Operation

Open the PC software, select the model, serial port, and baud rate (9600). Click the search button to find devices. Multiple cascaded device addresses can be searched.

Select the searched device address to view data from different modules.

Note: When cascading multiple modules, remember each module's MODBUS address. You can rotate the module to verify that the data displayed on the PC software corresponds to the correct module.

Sample Code

Link to download all sample code