Overview

The STD-20 is a microprocessor-based transmitter/controller designed for electrolytic conductivity measurement. It features two 4-digit LED displays for conductivity and temperature readings, MODBUS RTU communication, and 4-20mA output. The device supports high-accuracy salinity monitoring in industrial applications.

1. Safety Information (p.4-5)

• Electrical Hazards:
  • Ensure power isolation before installation or maintenance.
  • High voltage risks present; handle with care.
• Electrostatic Discharge (ESD) Precautions:
  • Avoid static electricity discharges.
  • Store and handle electronic components properly.

2. Storage Before Installation (p.6)

• Store in a dry, sheltered area to prevent environmental damage.
• Inspect all components for physical damage before installation.

3. System Description & Features (p.7)

• Microprocessor-based controller for electrolytic conductivity measurement.
• Dual LED display for conductivity and temperature readings.
• Power Supply: AC 100-240V (optional DC 24V).
• Alarms:
  • Power failure alarm.
  • Sensor failure alarm.
  • Salinity threshold alarm.
• Communication:
  • RS-485 MODBUS RTU.
  • 4-20mA analog output.

4. Technical Specifications (p.7-8)

• Measurement Ranges:
  • Salinity: 0 ~ 200 ppm (±5% FS accuracy).
  • Temperature: 0 ~ 100°C (±0.5°C accuracy).
• Sensor Features:
  • Electrode Cell Type: Isolated pocket-type.
  • Material: SUS316L, Naval Brass, POM.
• Power Requirements:
  • AC 100-240V, 0.25A, 50/60Hz (optional DC 24V).
• Alarm Relays:
  • Salinity alarm relay.
  • Power failure alarm relay.
  • Solenoid relay for salinity alarm.
• Protection Ratings:
  • Pressure Resistance: 20 BAR.
  • Ingress Protection: IP20.

5. Installation & Wiring (p.9-10)

• Power & Input Wiring:
  • AC L/N or DC 24V (+/-) input terminals.
  • Electrode cell connection for conductivity measurement.
  • PT100 RTD connection for temperature input.
• Output & Communication Wiring:
  • 4-20mA Output: Transmitter output for process monitoring.
  • RS-485 MODBUS RTU: Communication with ship loading computers, cargo monitoring systems, and alarm monitoring systems.

6. Operation & Calibration (p.11-16)

• Modes of Operation:
  • Initialization mode.
  • Calibration mode.
  • Setting mode.
• Calibration:
  • Temperature Calibration: Uses a 2-point RTD calibrator method.
  • Cell Calibration: Uses standard deionized water and salinity solutions (100, 200, 300, 400 μS).
  • 4-20mA Output Adjustment: Requires external ammeter and DC 12-36V power.

7. Alarm Handling (p.17-18)

• Sensor Alarm: Triggers when the sensor malfunctions (e.g., disconnected, damaged, or incorrect wiring).
• Salinity Alarm: Activates if the salinity value exceeds the user-set alarm threshold.

8. Communication Protocol (p.18-19)

• MODBUS RTU Settings:
  • Default Baud Rate: 9600bps, 8 data bits, 1 stop bit, no parity.
  • Salinity & Temperature Data Register Addresses:
    • Salinity (PPM): 0x1000
    • Temperature (°C in tenths): 0x1001
• Example MODBUS Command:
  • Read salinity & temperature:
    makefile

     

    Request: 01 03 10 00 00 02 C0 CB Response: 01 03 04 00 64 00 FC BB AD
  • Interpretation:
    • Salinity = 100 PPM
    • Temperature = 25.2°C

9. Sensor Installation & Replacement (p.19-21)

• Sensor Insertion:
  • Turn sensor nut counterclockwise before insertion.
  • Seal the connection with tape to prevent leaks.
• Sensor Replacement:
  • Loosen sensor nut.
  • Detach electrode cell and replace it with a new one.
  • Ensure O-rings remain intact to prevent water leakage.

10. Revision History (p.22-23)

• Version R6 (2025.03.03) – Sixth revision of the technical manual.