System Overview: Sperry Marine SR 120 Compact Gyrocompass
The Sperry Marine SR 120 (and companion SR 140 / SR 180 series) is a rugged, compact commercial gyrocompass engineered specifically for fishing trawlers, coastal cargo vessels, harbor tugs, and crew transfer vessels. Designed to deliver true heading accuracy in a space-saving chassis, the SR 120 uses a sealed, liquid-damped gyrosphere suspended in specialized silicone damping fluid with an electronic follow-up servo system.
The SR 120 features direct 24 V DC shipboard power operation, front-panel digital heading display, integrated latitude/speed error compensation, and multiple repeater outputs (step and serial NMEA 0183), making it an ideal reliable heading sensor for commercial vessels requiring minimal bridge footprint.
Technical Specifications: Sperry Marine SR 120
| Parameter | Specification Details |
|---|---|
| Model Designation | Sperry Marine SR 120 Compact Master Gyrocompass |
| Gyrosphere Element | Liquid-damped, sealed gyrosphere floating in silicone electrolyte suspension |
| Settling Time | Approx. 2.5 to 3 hours under normal operational temperatures |
| Static Accuracy | ≤ ±0.2° secant latitude |
| Dynamic Accuracy | ≤ ±0.5° secant latitude in sea states up to Force 6 |
| Follow-Up Speed | Up to 40°/second follow-up tracking rate |
| Outputs | 2x RS-422 NMEA 0183 ($HEHDT at 20Hz), 1x Step (24V DC), Failure Alarm Contact |
| Power Supply | 24 V DC nominal (18–32 V DC operational range); optional 115/230 V AC adapter |
| Power Consumption | Approx. 60 W operating (90 W starting) |
SR 120 Spare Parts & Maintenance Components
| Component | Part Number | Description & Function |
|---|---|---|
| SR 120 Gyrosphere | SR120-SPHERE | Factory-balanced sealed gyrosphere element |
| Supporting / Damping Fluid | SR120-FLUID-1L | Pre-measured silicone damping fluid bottle (1 Liter) |
| Follow-Up & Inverter Board | SR120-PCB-INV | Combined 3-phase gyro rotor inverter and follow-up motor driver |
| CPU & Display Board | SR120-PCB-DSP | Microprocessor controller with digital LED heading display and keypad |
| Follow-Up Stepper Motor | SR120-MTR-STP | Precision stepper motor driving azimuth ring gear |
| Power Filter & Regulator Board | SR120-PCB-PWR | DC/DC power conditioning board with reverse polarity protection |
| Drive Belt & Pulley Kit | SR120-BELT-KIT | Reinforced timing belt connecting follow-up motor to azimuth dial |
| Gasket & Seal Overhaul Kit | SR120-GSK-KIT | Silicone seals and container O-rings for periodic fluid service |
Seanav Service Procedures for SR 120
Seanav Marine provides certified maintenance and rapid replacement parts for the Sperry SR 120:
- Biennial Fluid & Seal Replacement: Draining silicone fluid, cleaning inner gimbal chamber, replacing container O-rings, and refilling with fresh fluid to maintain correct buoyancy.
- Azimuth Drive Inspection: Checking belt tension, inspecting follow-up gear teeth, and lubricating azimuth bearings.
- Digital Serial Calibration: Verifying RS-422 baud rate and update frequency ($HEHDT at 20 Hz / 38400 baud) for seamless autopilot and AIS operation.
- Power Supply Surge Testing: Testing 24V DC input filters against voltage sags and spikes during shipboard generator switchover.
