Application Paper


The COVID-19 pandemic has created a surge of severely ill patients whose only hope for survival is mechanical ventilation, which has created a global shortage of medical ventilators. Medical procurement agents are in fierce competition to purchase ventilators, factories are retooling to produce them, and grassroots engineering initiatives are in full swing. Never before has the global village been so united against a common threat.

Our partners at Unitronics, a leading manufacturer of integrated PLCs and HMIs, is helping to combat the ventilator shortage by providing automated ventilator control. The requirements of ventilator control are complex, however any ventilation mode, invasive or non-invasive, can be easily automated with Unitronics PLCs in order to comply with changes in recommended treatment.

In this application article, Unitronics provides general examples and guidelines for achieving Continuous Pressure Control using Unitronics PLCs, HMIs, and related components. But first, here is a quick overview of the Unitronic Medical Device Benefits:

  • Operating Panels display clear, waveform displays of patient status
  • Gloving: Touch Panels may be operated by gloved personnel
  • Quarantine: Access and control the Ventilator remotely, via mobile phone or tablet
  • Built-in Alarm system: set Alarms, send Alarm notifications to staff’s mobile phones
  • Manage Staff Access: easily set access levels, for example nurse, respiratory therapist, physician
  • Easy Integration with any CPR System
  • PLCs are 21 CFR Part 11 READY

Ventilator, Pressure Control, and Pressure Support Modes

This example is based on a UniStream PLC & HMI, controlling a Ventilator operating in Continuous Pressure Control mode. The Ventilator application shown below is displayed on the HMI screen—and may also be displayed on a mobile phone screen or tablet.

Via the HMI, medical staff can:

  • Access and change settings for:
    • Breathing Rate
    • Inspiratory / Expiratory Rate
    • Supplied Pressure
    • Positive End-Expiratory Pressure (PEEP) control
    • Oxygen level
  • View flow and pressure graphs
  • View and respond to Alarm notifications, via HMI screen or mobile
  • View ventilator and patient’s vital data, including:
    • Actual Pressure
    • Lungs Volume
    • Actual PEEP

Ventilator Application: General Functional Design

This diagram shows the general design and parameters of a typical Continuous Pressure system.

User Input Parameters
⇑ Rate [breath / min]
⇑ Inspiratory / Expiratory rate [% of breath cycle]
⇑ Airway Pressure [cm H2O]
⇑ Positive End-Expiratory Pressure (PEEP) [cm H2O]
⇑ Fraction of Inspired Oxygen (FiO2) [%]
⇑ Operational mode: Pressure Support / Pressure Control
⇑ Minimal volume alarm set-point [%]
⇑ Supplied air temperature and RH [%]
System Monitored Parameters (basic)

 Actual Pressure [cm H2O]
 Exhaled Tidal Volume [ml]
 Actual PEEP pressure [cm H2O]
 Graph – PEEP pressure
 Graph – Airflow

Operation Principles

This section covers the main principles of ventilation – Continuous Pressure mode and Pressure Support mode.

  • Manage Oxygen % levels using both Air and O2 proportional valves
  • Manage the breath cycle, according to defined rate and inspiratory / expiratory rate defined during the setup process
  • Stop ventilator operation in case of emergency input

Inspiratory management

  • Continuous Pressure Mode (Does not allow for patient-initiated breaths.)
  • During the inspiratory cycle, the system keeps the inspiratory valve open, and the expiratory valve closed
  • The system tracks the inspired air volume using the airflow sensor

Pressure Support mode (Allows the patient to breathe spontaneously)

  • When both inspiratory and expiratory valves are closed and pressure drops to “0” (during spontaneous breathing), the system opens the inspiratory valve to support the inspiratory process
  • The system tracks the inspired air volume using the airflow sensor

Expiratory management

  • During the expiratory cycle, the system keeps the expiratory valve open and the inspiratory valve closed, as long as the measured PEEP pressure is higher than the configured PEEP set-point value

Pressure Support mode

  • If the expiratory valve is closed and PEEP pressure ra

Alarms: General Principles

These are examples of situations that can trigger Alarms. Alarms will be displayed on the HMI screen, CRP recorded, and notifications can be sent to staff’s mobile.

  Inspiratory volume must be above the minimal volume defined

  Leakage Detection – If tank output pressure does not reach the set airway pressure

  During the expiratory process, PEEP pressure must fall. If there is no change during the minimal timeout period, set alarm (Valve Fault)

  During the inspiratory cycle, airflow pressure must fall (timeout delay). If it does not, set alarm (inspiratory valve fault)

  Supplied air temperature low

  Supplied air temperature high

  Filters replacement


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