The anemometer gives false readings. Troubleshooting

Greetings! Today we have a problem with the anemometer, which shows the wind speed and direction on the bridge. The readings were stuck in one direction (opposite to the wind). At this speed the wind is displayed correctly.

What is an anemometer?

An anemometer (or anemoscope) is a weather vane that consists of a generator, a synchronous motor, bearings, gear guides, rings and a brush device. All this can be said in one name - transmitter.

Block diagram of anemometer operation

When the direction of the wind changes, the weather vane changes its position to the current angle, and at the same time the position of the synchronous motor changes.

An anemometer on a vessel is a device used to measure wind speed and direction. It is a crucial instrument for navigation and safety on ships, providing real-time data that helps in the following ways:

1. Navigation: Accurate wind data helps in plotting the best course and optimizing fuel efficiency by taking advantage of favorable winds.
2. Safety: Knowing the wind speed and direction is essential for ensuring the safety of the vessel, crew, and cargo, especially during adverse weather conditions.
3. Sail Adjustments: For sailing vessels, anemometers are vital for adjusting sails to optimize performance and prevent damage from sudden gusts of wind.
4. Weather Monitoring: It aids in monitoring and predicting weather conditions, helping the crew prepare for changes in the environment.

The anemometer typically consists of rotating cups or propellers that spin at a rate proportional to the wind speed. This data is then transmitted to the ship’s monitoring systems for analysis and decision-making.

How Wind Direction Is Measured in the Heriana AT-200 Anemometer

Operating Principle of Wind Direction Measurement

In the Heriana AT-200, wind direction is determined by the rotation of the tail vane (weather vane), which keeps the propeller aligned with the wind. This rotation is mechanically transferred to a position-sensing device, most likely implemented in one of the following ways:

1. Synchro Transmitter (Most Likely Method)

• This is the most probable mechanism used in the AT-200, especially since the system operates on 110V AC.
• The tail vane is mechanically connected to the rotor of a synchro transmitter.
• As the wind shifts, the rotor turns, and the stator windings produce a three-phase AC voltage.
• The relative amplitudes of these signals represent the angular position (i.e., wind direction).
• These signals are sent to a wind direction indicator, which processes and displays the direction in degrees.
• This method is robust, accurate, and well-suited for marine environments.

2. Potentiometer-Based Sensor (Used in Simpler Designs)

• Some direction sensors use a precision rotary potentiometer.
• The vane shaft turns a potentiometer wiper, producing a voltage proportional to the angle (e.g., 0–5 V = 0–360°).
• While simpler and cheaper, this method is less reliable in marine settings due to wear and corrosion.

3. Optical or Magnetic Encoders (Unlikely for AT-200)

• More advanced or digital wind sensors may use optical encoders or magnetic position sensors.
• These provide high-resolution digital signals but are unlikely to be present in the analog-driven AT-200.

Signal Transmission

• In the case of the synchro transmitter:
• The three-phase signal is transmitted to a bridge-mounted indicator, which converts it into a degree value (0–360°).
• In some setups, this analog signal is digitized and sent via NMEA 0183 or RS422 to ship systems or navigation displays.

In the Heriana AT-200, wind direction is measured using a synchro transmitter, not a potentiometer. The vane’s mechanical rotation produces a three-phase analog signal whose voltage ratios represent the wind direction.

Receiver (transformer box)

As a result, receiver (transformer box) receives voltage and processes (according to the diagram - a transformer box), and the wind direction is displayed on the panel indicator.

A synchronous motor in an anemometer (typically in cup-type or propeller-type anemometers) serves as part of a speed-to-frequency conversion mechanism, translating wind speed into an electrical signal. Here’s how it works:

Basic Working Principle:

1. Wind Speed Rotation:

• Wind moves the cups or propeller of the anemometer.
• This causes a rotating shaft to spin at a speed proportional to the wind velocity.

2. Synchronous Motor as Generator:

• In some designs, a small permanent magnet synchronous motor (PMSM) is connected to the rotating shaft.
• When the rotor (magnet) spins, it induces a voltage in the stator coils.
• The frequency of this voltage is directly proportional to the rotational speed, which in turn is proportional to wind speed.

3. Frequency Output:

• The induced AC signal is then processed by electronics to calculate wind speed based on frequency (e.g., 1 Hz = 1 m/s or similar calibration).

Why Use a Synchronous Motor?

• Precise speed-to-frequency relationship: Unlike induction motors, synchronous motors spin at a speed locked to the frequency (or vice versa when used as a generator).
• Simple signal processing: Frequency signals are easier and more reliable to measure electronically than analog voltages in harsh outdoor conditions.
• Low power and durable: These motors can operate with very little torque input and have long life due to minimal friction if bearings are good.

In an anemometer, a synchronous motor acts like a tiny AC generator, where the wind drives its rotor, generating an AC signal. The frequency of this signal corresponds to the wind speed, allowing for accurate measurement.

Indicator panel

Force of the wind measures using a propeller and generator. The voltage of the generator is converted and reads by the voltmeter, which displays the wind speed in meters/sec (or knots) on the panel indicator.

General diagram of the anemometer operation

Indicator panel. The anemometer is stuck at 173˚ port side, although it should show about 30˚ starboard side.

From the experience of maritime practice, you can immediately turn to the signal transmitter, because it is who continues the action of the aggressive marine environment, as well as the force of the wind. Most often the problem can be stored there. Therefore, first of all, let's open the weather vane junction box and see what happens to the synchronous motor and brushes.

Synchronous motor and anemometer brush apparatus

As a result of an internal check of the anemometer, a problem was discovered with the half-coupling on the synchronous motor shaft, unscrewed mounting bolt (under the hex key). When the weather vane shaft rotated, the motor shaft stood still, so the position of the anemometer was stuck in one position.

Video of the coupling operation

Brushes are a group of thin hairs, which on old anemometers can severely lose their rigidity and intertwine with each other, which also leads to incorrect consequences.

The coupling was retightened, the brush device was cleaned of graphite dust. The readings began to change, but they were still incorrect (180˚ opposite).

Such systems must have a zero calibration. In this case, it can be found on the receiver board.

ZERO SET (zero calibration) on the receiver board

You must first fix the weather vane in the zero position so that it does not rotate. The propeller also needs to be fixed (not shown in the photo). You can use an assistant or a rope.

Fixed the transmitter in the zero position (tied it by the tail to the Light tree)

We switched the ZERO SET switch to the right and set the indicator to zero.

Zero on the indicator

After this, the switch returned to its normal position and the weather vane was untied. As a result, the operation of the anemometer was recovered.

If it is not possible to set zero and the anemometer is accurately twisted by 180˚, then you can temporarily reverse the phase on the receiver.

Switching phases on the receiver

This is a temporary emergency solution. Subsequently, it will still be necessary to correctly connect the phase and perform a zero calibration.

What other problems could be with the anemometer?

The most common problems that can occur with anemometers are the stuck of the bearings, burning out of the internal components (generator and synchronous motor), which results in the water inside the transmitter.

I also suggest that you read the manufacturer’s instructions for troubleshooting the anemometer.

Troubleshooting anemometer

Anemometer (anemoscope) model: Wind sensor (propeller type) AT-200. Heriana

Video of normal operation of the anemometer

The Heriana AT-200 is a marine-grade propeller-type anemometer designed to measure both wind speed and direction, commonly used in maritime navigation systems. The AT-200 uses a mechanical sensor mechanism that uses a synchronous motor or similar rotary transducer to convert wind-induced rotation into electrical signals.

How the AT-200 Operates

1. Wind-Driven Propeller: The anemometer features a propeller that rotates in response to wind, with the rotational speed corresponding to wind velocity.
2. Synchronous Motor Functionality: The rotating propeller shaft is connected to a synchronous motor or a similar device that acts as a generator. As the shaft turns, it induces an alternating current (AC) signal whose frequency is proportional to the rotational speed, and thus to the wind speed.
3. Signal Transmission: The generated electrical signal is transmitted to a display unit or integrated into a ship’s navigation system, providing real-time wind speed and direction data. 

This method ensures a direct and reliable correlation between wind speed and the electrical output, facilitating accurate measurements even in challenging marine environments.

Maintenance and Calibration

For optimal performance, regular maintenance is recommended, including:

• Cleaning: Remove any debris or salt deposits from the propeller and housing to prevent obstruction and corrosion.
• Lubrication: Ensure that moving parts, such as bearings, are adequately lubricated to reduce wear and maintain smooth operation.
• Calibration: Periodically verify the accuracy of the anemometer against known standards or reference instruments, especially after exposure to severe weather conditions.

Adhering to these maintenance practices helps ensure the longevity and accuracy of the AT-200 anemometer in measuring wind parameters.

If you had experience in repairing and operating this device, write in the comments to the article or in official groups of site on social networks.