The process is seen as millions of tiny bubbles impacting against the instruments within the tank and is what dislodges any particles present. The process can be made more efficient with the introduction of heat and by adding detergent to to the cleaning liquid.

To obtain reliable effective results, ultrasonic cleaners require regular maintenance and testing. The routine testing of ultrasonic cleaners can be divided into time periods: Daily, weekly, quarterly and annual tests.

Table showing required tests and frequency

Test	Daily	Weekly	Quarterly	Yearly
Automatic Control Test	Y	Y	Y	Y
Safety Checks		Y	Y	Y
Cleaning Efficacy		Y	Y	Y
Ultrasonic Activity			Y	Y

Automatic Control Test

This is an observational test that aims to ensure that the machine is operating its cycle within the required specification by visually monitoring the machine's own instruments. It is reliable to use the machine's own instruments as these are checked quarterly during the 'Verification of Calibration of Machine Instruments' test. A stopwatch is required so that each stage of the cycle can be timed, and all data should be recorded within the machine's own logbook.

The principle behind the Automatic Control Test is to create a continuous performance record that is unique to the machine. This ensures that any deviation from normal performance can be identified.

If the machine has a printer installed, the Daily Automatic Control Test may be replaced by attaching a printout to the machine's logbook, however this is at the discretion of your Authorizing Engineer.

A successful Automatic Control Test for an Ultrasonic Cleaner should comprise of:

• The cycle time and temperature remains consistant with results of previous tests
• The machine should display 'Complete Cycle' message
• There is no observed deviation from normal performance
• Machine logbook is updated

Safety Checks

Safety checks ensure Operator Safety and correct cycle function and usually consist of:

• Safety valve operation
• Door pressure interlock
• Door cycle start interlock
• Door in-cycle interlock
• Condition of door seal
• Cleaning of filters and strainers
• Check of spray arms for free movement (If relevant)
• Check of spray nozzles for blockage (If relevant)

Not all checks are required daily, however it is at the discretion of your Authorizing Engineer as to the regularity of the tasks listed.

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Cleaning Efficacy

Cleaning Efficacy tests are done to prove that the machine is reducing the amount of contamination on an instrument to an acceptable level during the cycle. Due to the extent of contamination that occurs both naturally and during use it is impossible to test for every possibility. Protein is a component of the majority of contaminations so it is this that most test methods focus on.

The most common test is the Ninhydrin method where a processed object is swabbed, ninhydrin solution is applied to the swab, then incubated. If any protein has been picked up by the swab, the Ninhydrin will cause a colour reaction indicating possible contamination.

The Ninhydrin method can be used to test an actual surgical instrument that has been contaminated through theatre use, or a surgical instrument or Surrogate Device coated in Test Soil.

A Surrogate Device is used to mimic the characteristics of a surgical instrument. Due to the value of some surgical instruments, a Surrogate Device provides an economic alternative that still provides an acceptable process challenge.

Test Soil is used to mimic contaminants that would be found on an instrument prior to processing. Test Soil is available in a variety of forms and it is down to your Authorizing Engineer to dictate the preferred type.

When testing using the Ninhydrin method a successful test should comprise of:

• Take three swabs.
• One swab should be contaminated with protein, treated with ninhydrin and incubated. This will tell you what to look for in a 'fail' result ie: protein is present.
• One swab should be treated with sterile water, ninhydrin and incubated. This will tell you what to look for in a 'pass' result ie: protien is not present.
• One swab should be treated with sterile water, swabbed against a processed instrument or surrogate device, and incubated. This should then be compaired with the 'fail' and 'pass' results to determin the outcome of the test. If there is purple discolouration on the swab it is an indication that protein is present.
• Machine logbook should be updated.

Ultrasonic Activity

The ultrasonic activity is tested to check that the cleaner is cavitating correctly. The HTM recommended proceedure is the Aluminium Foil Test.

Nine strips of aluminium foil are cut to a width between 15mm and 20mm, and a length of bath depth +120mm. The end of the foil strip should be rolled so that the strips are weighted down during the test. Using autoclave tape across the bath, the foil should be suspended evenly in the bath in a 3x3 grid, with the end of the foil no more than 10mm from the bottom of the tank. After a complete cycle, the foil strips are checked. A successful Aluminium Foil Test should produce approximatly the same erosion pattern on all nine strips, indicating an even distribution of cavitation throughout the Ultrasonic Cleaner.

There are also alternative methods to the aluminium foil test. A test meter is available that measures both frequency and percentage power, which can be logged and used to provide a comparison over a period of time, whilst cavitation can also be measured with test vials that provide a chemical colour change reaction. Alternate methods to the foil test are at the diecretion of your Authorizing Engineer.