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The JRC JLN-740A is an IMO type-approved, single-axis (Speed Through Water – STW) Doppler Speed Log designed for commercial vessels above 300 GT. The “A” model designation denotes the 4-unit system configuration (incorporating a dedicated Distribution Processor unit alongside the signal processor, main display, and transducer) intended for expanded sensor output distribution across bridge networks.
Operating on a 2 MHz dual-beam pulse Doppler frequency, the JLN-740A utilizes digital signal processing to deliver high-precision speed tracking (down to 0.03 knots or 0.3% error at constant speeds). It features JRC’s proprietary bubble detection technology, which automatically monitors and alerts bridge staff if aerated water/bubble interference reduces speed measurement accuracy.
Dual-Beam 2 MHz Doppler Engine: Uses high-frequency pulse Doppler beams to measure Speed Through Water (STW) with enhanced response rates during low-speed berthing maneuvers.
Proprietary Bubble Detection: Continuously checks transducer face contact; flags aeration warnings on the display to eliminate false maintenance checks caused by hull bubbles.
4-Unit Expanded Architecture (Model A): Includes the NQA-7040 Distribution Processor, providing ample serial, analog, and pulse outputs for ECDIS, Radar, VDR, and slave repeaters.
Color Touch Screen Display (Option/Standard): Available with a 5.1-inch color touch-panel LCD display (NWZ-510SDW) or standard 4.5-inch monochrome display, offering intuitive night dimming and operational modes.
JRC RMS Compatibility: Integrates with JRC’s Remote Maintenance System (RMS) via LAN for remote health diagnostic reporting.
| Category | Component / Feature | Technical Specification |
| System Model | Model Identifier | JRC JLN-740A (4-Unit Configuration) |
| Measuring Principle | System Type | Single-Axis Dual-Beam Pulse Doppler Speed Log (Speed Through Water) |
| Operating Frequency | 2.0 MHz | |
| Water Speed Range | -10.00 to +40.00 knots | |
| Depth Below Transducer | Effective measuring depth $\ge$ 3.0 meters below transducer face | |
| Speed Accuracy | $\pm 1\%$ or $\pm 0.1$ knots (whichever is greater) / $\pm 0.03$ kn / 0.3% at constant speed | |
| Distance Accuracy | $\pm 1\%$ or $\pm 0.1$ NM/hour | |
| Displays & Control | Main Display Unit | NWZ-510SDW (5.1″ Color LCD, 480 x 800 resolution with Touch Panel) |
| Sailing Display Range | 0 to 999,999.99 NM (Model A extended range) | |
| System Units (4-Unit Set) | Core Modules |
1. Main Display (NWZ-510SDW) 2. Distribution Processor (NQA-7040) 3. Signal Processor (NJC-70S) 4. Transducer Unit (Flat type NKF-547 or Gate Valve) |
| Interfaces & Connectivity | NMEA Output Ports | Up to 8 x IEC 61162-1 / NMEA 0183 Outputs (VBW, VLW sentences) |
| NMEA Input Ports | 1 x IEC 61162-1 GPS Input (RMC, ZDA) | |
| Analog Outputs | 2 x Analog Speed Outputs | |
| Pulse Outputs | 2 x Contact Closure Log Pulse Ports (200 pulses/NM) | |
| Network & Remote Ports | 1 x LAN Port (JRC RMS Support), 2 x Remote Display Ports (NWZ-650SDR / NWZ-840SDR / NWZ-4610) | |
| Contact Alarms | Power Fail, Speed Out of Range, and System Fail relay contacts | |
| Electrical & Physical | Power Supply Input | 100 / 230V AC $\pm 10\%$ (50/60 Hz) |
| Power Consumption | $\le 50\text{ W}$ (60 VA at 100V / 150 VA at 230V) | |
| Operating Temperature | -15°C to +55°C | |
| Standards & Approvals | Certifications | IMO MSC.96(72) Compliant, MED Wheelmark, IEC 61023, IEC 60945 |
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