Healthcare Facility Project: Shenzhen Nanshan Hospital

PLC Control Cabinets in Hospital Applications: Critical Functions & Implementations

Core Application Scenarios

A. Life Support Systems

Medical Gas Control

• Function: Regulates the pressures of oxygen ($O^2$), nitrous oxide ($N^{2}O$), and vacuum systems within the range of 0.4–0.55 MPa, ensuring pressure fluctuations remain below 1%.
• PLC Role: Monitors pipeline pressures using analog input signals (4 - 20 mA). Triggers alarms if pressure thresholds (as specified in EN ISO 7396 - 1) are violated.
• Safety: Enables automatic shutoff during fire alarms to comply with NFPA 99 standards.

HVAC for OR/ICU

• Precision Control: Maintains air cleanliness at ISO Class 5, with temperature ranging from 20 - 24 °C and relative humidity (RH) between 40 - 60%.
• PLC Logic: Implements variable frequency drive (VFD) - driven laminar flow control, maintaining air velocity at 0.25 - 0.35 m/s. Monitors differential pressure (DP) of HEPA filters.

B. Power Management

Critical Load Transfer

• Implementation: Automatically starts the genset within less than 10 seconds when a grid failure occurs, in line with UL 1008 requirements.
• PLC Logic: Utilizes a dual - source automatic transfer switch (ATS) with closed - transition switching.

Harmonic Mitigation

• Solution: PLC - controlled active filters reduce harmonics generated by MRI and CT equipment to less than 5% total harmonic distortion (THD).

C. Laboratory Automation

Biosafety Cabinets

• Control: Maintains a face velocity of 0.5 m/s while dynamically adjusting the sash position.
• Data Logging: Stores operation records that comply with 21 CFR Part 11.

Specialized Control Requirements

EMC Considerations

Shielding

• Enclosures compliant with MIL - STD - 461G are used in MRI zones to ensure electromagnetic compatibility (EMC).

Noise Immunity

• Optical isolation is employed for ECG/EEG equipment to meet IEC 60601 - 1 - 2 noise immunity requirements.

Redundancy Design

Architecture

• Uses dual hot - standby CPUs (SIL 3) for dialysis machines to ensure operational continuity.

Failsafe

• Incorporates watchdog timers with a failover time of less than 100 ms.

Operational Benefits

Patient Safety

• Prevents errors in the mixing of anesthetic gases through interlocked valve control.

Energy Efficiency

• Achieves a 30% reduction in HVAC energy consumption through occupancy - based ventilation strategies.

Maintenance Optimization

• Employs predictive algorithms to detect pump bearing wear via vibration fast Fourier transform (FFT) analysis.

• Implementation Examples

• Department	PLC Model	Key I/O Configuration
  OR Suites	Siemens S7 - 1500	16 AI (PT100), 32 DO (24 VDC)
  Pharmacy	Allen - Bradley CompactLogix	8 - axis servo control
  Central Sterile	Omron NJ501	EtherCAT - connected SCARA robots