System monitors hospital sterilisation

Edited by the Engineeringtalk editorial team Aug 24, 2007

The autoclave monitoring system makes maximum use of the mathematics functions incorporated in the Daqstation, which are enhanced by the extended length of the mathematics channels.

The Network Solutions Division of Yokogawa UK has collaborated with steriliser manufacturer BMM Weston to develop an independent monitoring system for the autoclaves used for hospital and pharmaceutical sterilisation.

The system is based on the Yokogawa Daqstation range of paperless recorders.

Autoclaves implement the sterilisation process by exposing the objects to be sterilised to pulses of high-temperature steam at high-pressure.

Traditionally, these instruments have been run by programmable logic controllers (PLCs) or bespoke microprocessor systems.

They typically incorporate a printer to print out information about the temperature and pressure from each sterilisation process, including 'pass/fail' information confirming that the unit has reached the required temperature for the specified time.

Paperless or chart recorders are often a requirement to provide independent monitoring of each run from separate sensors to prove that what the steriliser reports actually happened.

Currently, many autoclave users have to manually check the independent monitor results, which can be very time-consuming.

Now, however, the system developed by BMM Weston and Yokogawa automates this process and produces results which are fully compliant with the various standards including 21CFR11 for the pharmaceutical industry and the European EN554/EN285: Appendix D.

With the new system, the PLC or microcontroller in the autoclave sends information on the time, number of pulses, sterilisation temperature and pressure to the recorder via industry-standard communications interfaces.

The recorder automatically counts the number of pulses during three sets of pressure pulses according to the pre-programmed micro recipe, and checks that the temperature is within the specification for a given time period.

It also checks, via steam tables, that the temperature is within the specification, calculated from the steam pressure.

The autoclave's controller then interrogates the Daqstation to detect 'pass/fail' results, and prints out the result of the independent monitoring system.

If the result is a 'pass', the user does not have to check the file.

The results are simply stored.

For the new system, BMM Weston developed a link between the company's existing control software and the recorder, and specified the requirements for the equations used by the recorder to calculate the results.

BMM Weston and Yokogawa then worked closely together to implement the equations within the recorder.

The independent monitoring system makes maximum use of the mathematics functions incorporated in the Daqstation, which are enhanced by the extended length of the mathematics channels and the number of channels.

In particular, it detects low-to-high and high-to-low transitions of pressure pulses to count them in each stage of the cycle, as well as counting the time during which the temperature is within the sterilisation band.

It also checks that the temperature derived from the steam tables value matches the actual temperature.

In addition to the time saving that results from the automation of a previously time-consuming process, the new system has the major additional benefit of reducing the possibility of human error, ensuring greater accuracy and reliability of results in the long-term.