All,
Any one has any experience of having an issue with the timer or clock in a autoclave? The time of exposure seen on the print out / measured with a stop watch did not meet the one set in the cycle parameters. It is more by about 10% of the set time.
Is the clock/time stamp in autoclave usually verified or calibrated?
Any thoughts are welcome and will be useful.
US FDA
I too have experienced a difference between the exposure time set in the cycle parameters and the measured exposure time.
I would like to define measured exposure time: The measured exposure time starts when the slowest heating sensor reaches the sterilization temperature. E.g. the sterilization temperature is 250 °F. It ends when the fastest cooling sensor drops below the sterilization temperature.
Since the measured exposure time is based on temperature it will be affected by the temperature sensor’s response time. This means that it takes time before the temperature sensor is reading 100 % of the actual autoclave temperature. Also, the exposure time will be affected by the position of the temperature sensor. E.g. if the sensor is measuring inside a product it will heat slower compared to being positioned in the autoclave chamber.
Time is a critical validation parameter. This is why measuring equipment that time stamps each reading should undergo a chronometric calibration periodically.
The exposure time set in the cycle parameters can be measured by logging the signals controlling exposure start and exposure end. The signals can be logged by connecting a data logger to the autoclave’s PLC. In this way, the the signals can be viewed in the same graph showing the temperature profile. This makes it possible to correlate cycle exposure time and measured exposure time and thereby assess the performance of the autoclave.
I hope this is useful.
Best regards,
Enrique Riis
Comparing an autoclave exposure timer to a stop watch should be a thing of the past. In the old days when autoclaves used electro-mechanical timers (wind-up type), there was a margin for error, but with a digital timer this is highly unlikely over a typical exposure phase.
The deviation that you are seeing is probably due to the machine characteristics on when the timer is triggered.
Some machines have a built in lag time for liquid cycles. If Fo control is used, there may be a discrepancy. Was it possible that the temperature dipped below set point during exposure and the timer stalled?
‘The exposure time set in the cycle parameters can be measured by logging the signals controlling exposure start and exposure end. The signals can be logged by connecting a data logger to the autoclave’s PLC.’
Thanks for your information.
Can you please give more info on how to get this done using validator and thermocouples?
US FDA
F0 control is not used. It is set for time only.
No. Temp did not dip below set point.
The printing interval set in cycle parameters - every 60 seconds - is not being fulfilled. It prints every 64 seconds for most of the sterilization phase. For some, it maintained the 60 seconds - but very few. In short-- erratic.
I am looking at the sterilization phase only.
Thanks
US FDA
[quote=gphillips]Comparing an autoclave exposure timer to a stop watch should be a thing of the past. In the old days when autoclaves used electro-mechanical timers (wind-up type), there was a margin for error, but with a digital timer this is highly unlikely over a typical exposure phase.
The deviation that you are seeing is probably due to the machine characteristics on when the timer is triggered.
Some machines have a built in lag time for liquid cycles. If Fo control is used, there may be a discrepancy. Was it possible that the temperature dipped below set point during exposure and the timer stalled?[/quote]
Does the time stamp on the printout indicate that it is printing at 60s intervals? Are you timing when you actually see the printer operate? It may just be buffering.
What brand of autoclave is it?
I do not have this information for validator and thermocouples. However, it is possible using TrackSense Pro wireless data loggers from Ellab. Please see the description of the AutoMarker following this link:
http://www.ellab.com/Products/Validation/TrackSense_Pro/Data_Loggers/Pro/Sensors.aspx
Best regards,
Enrique Riis