Complete Guide to On site Maintenance and Troubleshooting of Honeywell TN3801 Electro Motive Liquid Level

Sensor calibration: Use a high-precision pressure source (0.05 level) to perform full-scale linearity calibration on all channel back pressure sensors.

Cleaning of flow regulator: Remove the flow regulator from each channel and use anhydrous alcohol ultrasonic cleaning to remove oil sludge.

Communication redundancy test: Manually disconnect COM1, confirm that the system automatically switches to COM2 and the data is continuous without interruption.

Backup channel test: If the cabinet is not fully equipped, a backup bubble tube can be pre installed using the backup channel to quickly replace the faulty channel.

5.4 Recommended spare parts

Automatic non return valve component (1 piece for every 8 channels)

Flow regulator (1 piece for every 16 channels)

Back pressure sensor (1 piece per cabinet)

Air filter cartridge (matching filter unit)

Key points of communication integration and software configuration

As a slave station of the ship automation system, TN3801 needs to be correctly integrated with the main station (such as PLC, HMI, AMS). The following are details that are easily overlooked in actual projects:

6.1 Modbus Register Mapping

By default, TN3801 stores the liquid level value for each channel as a 16 bit integer, measured in 0.1% FS or centimeters (depending on the configuration). For example:

Register Address 40001: Channel 1 Liquid Level (Floating Point or Integer)

Register address 40002: Channel 2 liquid level, and so on

Please refer to Chapter 4 of Technical Manual MT5015 for a detailed address table.

6.2 Baud rate and communication parameter settings

It can be set through the TN3801 internal DIP switch or display unit menu:

Optional baud rates: 2400, 4800, 9600, 19200, 38400

Data format: 8N1 (default), 8E1, 8O1

Station address: 1-247

Attention: After modifying communication parameters, it is necessary to power on again or perform a soft reset to take effect.

6.3 Redundant Port Wiring Example

Two RS485 ports can be connected to two different main stations (such as the main PLC and backup PLC) using a "daisy chain", or one to the local display and the other to the upper computer. When wiring:

Port A: T+/R+connected to main station A (+)

Port B: T -/R-connected to main station B (-)

The common terminal (GND) must be connected to the main station signal ground to avoid common mode voltage damaging the interface.

Selection and replacement upgrade suggestions

Upgrading to TN3801 can bring significant benefits to ships that are still using early electrical level measurement systems, such as single channel pneumatic transmitters and old models without Modbus communication

Reduce the risk of leakage by replacing multiple pneumatic pipelines with a single multi-core cable.

Digital integration: directly connected to ship Ethernet or fieldbus without the need for additional signal converters.

Redundant communication: Improve the availability of monitoring systems.

Low maintenance: Automatic flow regulation and self diagnostic functions significantly reduce manual inspections.

Attention should be paid when replacing:

The original bubble tube can continue to be used by simply connecting the gas outlet of TN3801 to the existing pipeline.

The power supply voltage must match: TN3801 supports 115/230 VAC switching, please confirm when ordering.

If the original system uses 4-20 mA analog signals to the alarm panel, TN3801's analog output module (4-20 mA per channel) can be optionally equipped to achieve seamless replacement.

Case study: No reading of the whole machine caused by gas source pressure loss

Background: A 100000 ton oil tanker reported that the liquid level displayed in all channels of TN3801 was 0 (the lowest value), and the ship was in a ballast state but the actual ballast tank was full.

Troubleshooting process:

Step 1: Check the air supply pressure gauge of the cabinet, the pointer is at 0 bar. Inquired about the engine room and found that the main air compressor of the ship had tripped and the backup air compressor had not automatically started.

Step 2: Restore power to the air compressor, wait for the air pressure to rise to 7 bar, and gradually restore the TN3801 liquid level reading to normal within 30 seconds.

Step 3: Check the non return valve status, all valves are open normally and there is no backflow phenomenon.

Conclusion: After the gas source is interrupted, the non return valve closes to protect the internal sensor. After the gas supply is restored, the system automatically returns to normal. Suggest adding an independent small gas storage tank (20 L) to TN3801 to cope with short-term gas source fluctuations.