Core Basis for Instrument and Electrical Division

The responsibility area division between instruments (automation instruments) and electrical (electrical engineering) must follow the principles of "clear boundaries, avoiding overlap, and efficient collaboration". It is mainly defined based on signal types and equipment functions to ensure stable operation of industrial systems.

Signal Types

  • Instrument: Responsible for equipment and circuits of analog signals (4-20mA, 0-10V, etc.) and digital signals (switch signals, communication signals such as HART, PROFINET, etc.).
  • Electrical: Responsible for equipment and circuits of high-power signals (AC 380V/220V, DC 220V, etc.) and motor control signals (contactor, relay circuits).

Equipment Functions

  • Instrument: Focuses on "measurement, control, regulation", such as sensing process parameters (temperature, pressure, flow) and executing control commands (valve actions).
  • Electrical: Focuses on "power supply, power drive", such as providing power, controlling motor start/stop, and ensuring electrical safety of equipment.

Instrument Responsibility Area

Instruments are responsible for equipment related to measurement, control, execution, and signal circuits.

Measurement and Detection Equipment

  • Various sensors: temperature (thermocouple, RTD), pressure (transmitter, pressure gauge), flow (flow meter), level (level gauge), composition (analyzer), etc.
  • Switch-type equipment: level switch, pressure switch, flow switch, safety interlock switch (such as emergency shutdown button ESD).

Control and Execution Equipment

  • Control units: DCS/PLC systems (including cards, modules, instrument-side wiring in control cabinets), remote IO stations, safety instrumented systems (SIS).
  • Actuators: pneumatic/electric control valves, valve positioners, solenoid valves (control circuit part), servo motors (control signal part).
  • Communication equipment: industrial Ethernet switches (instrument communication network), wireless gateways, HART/FF bus devices.

Signal Circuits

  • Analog signal circuits: 4-20mA signals from sensors to DCS/PLC, control signals from DCS to actuators.
  • Digital signal circuits: switch input (DI), switch output (DO) circuits (such as solenoid valve control signals).
  • Communication circuits: bus communication between instrument devices (PROFINET, Modbus, HART, etc.).

Auxiliary Equipment

  • Instrument air supply system: air purification devices (filters, dryers), air supply pipes (usually DN≤25mm).
  • Instrument power supply: 24VDC power supply (circuits supplying power to transmitters, positioners, etc.).
  • Calibration equipment: standard instruments (such as calibrators, multimeters) and measurement instrument management.

Electrical Responsibility Area

Electrical is responsible for equipment related to power supply, power drive, and electrical safety.

Power Supply System

  • High-voltage equipment: high-voltage switchgear, transformers, high-voltage cables.
  • Low-voltage equipment: low-voltage distribution cabinets (MCC), circuit breakers, fuses, contactors, relays (high-power control circuits).
  • Power circuits: 380V/220V AC power supply circuits, DC panels (220V/110V DC power supply).

Power Equipment

  • Motors: AC asynchronous motors, DC motors, variable frequency motors (including motor body and wiring).
  • Variable frequency equipment: frequency converters (high-power main circuit and power supply side), soft starters.
  • Electrical drive: motor control circuits (contactors, thermal relays, overload protection).

Electrical Safety Equipment

  • Grounding system: protective grounding, working grounding, lightning protection grounding (including grounding electrodes, grounding wires).
  • Lightning protection equipment: surge protectors (power supply side), lightning rods.
  • Lighting and emergency systems: workshop lighting, emergency lighting, explosion-proof luminaires.

High-Power Circuits and Wiring

  • Power cables: motor cables, connecting cables between distribution cabinets (cross-sectional area usually ≥4mm²).
  • Electrical cable trays: high-power cable trays (laid separately from instrument cable trays to avoid interference).
  • On-site electrical boxes: power distribution boxes, motor control boxes (excluding remote IO boxes for instruments).

Principles for Dividing Cross-over Areas

Cross-over areas require clear division of responsibilities between instruments and electrical to ensure efficient collaboration.

DCS/PLC Control Cabinet

  • Instrument responsibility: internal instrument cards, modules, instrument-side wiring terminals (analog/digital signals).
  • Electrical responsibility: main power switch in the control cabinet, 220VAC power supply circuits, grounding terminals (high-power part).

Solenoid Valve and Motor Control

  • Solenoid valve: Instrument is responsible for control signals (24VDC DO circuits), electrical is responsible for the 220VAC power circuit of the solenoid valve.
  • Variable frequency motor: Instrument is responsible for control signals (such as 4-20mA speed command), electrical is responsible for the frequency converter power supply, motor main circuit, and overload protection.

Communication and Power Supply

  • Shared power supply (such as 24VDC supplying power to instruments and small electrical equipment): Electrical is responsible for the main power switch and incoming line, instrument is responsible for branches and loads.
  • Industrial network: Instrument is responsible for communication of instrument devices, electrical is responsible for communication of motors, frequency converters, and other equipment (such as PROFINET to motor starters).

Explosion-Proof Area Equipment

  • Instrument is responsible for the selection, installation, and sealing of explosion-proof instruments (transmitters, flow meters).
  • Electrical is responsible for the selection, wiring, and grounding of explosion-proof motors, luminaires, and switches.

Fault Handling and Collaboration Mechanism

Clarifying fault handling procedures and collaboration mechanisms can avoid shifting responsibilities and ensure stable system operation.

  • Fault handling: If equipment abnormality is caused by signal issues, check the instrument signal circuit first; if caused by power supply issues, electrical should troubleshoot.
  • Modification projects: Instrument submits control signal requirements, electrical is responsible for the power supply plan, and both jointly confirm the interface (such as signal type, power parameters).
  • Document management: Instrument is responsible for control logic diagrams and signal circuit diagrams, electrical is responsible for electrical schematic diagrams and power supply system diagrams, and equipment lists are shared.

Through clear division, "shifting responsibilities" can be avoided, and a collaboration mechanism is established in cross-over areas to ensure stable operation of industrial systems. Different enterprises may have slight differences due to industry characteristics (such as chemical, power), but the core logic is consistent.