pH Knife ProbeAbout pH Knife Probe Replacement Sensor This product listing is for a replacement sensor. You can purchase the single probe or full kit by clicking on the options on the dropdown box above. The pH knife probe has been developed for use in the food industry for the testing of frozen or semi frozen foodstuffs. The stainless steel Knife protects the pH electrode from damage, but does not in any way prevent the glass sensor from effectively measuring the