For Compliance Verification periodic testing, how frequently should an ESD control item be checked?
It is user defined, so it is up to you. Best practice is to test each and every ionizer, but you could also decide (if you got good results) to test a percentage of a particular ESD control item. The frequency and sampling percentage should be documented in your written ESD control plan. Depending upon your test results, you would then want to tighten or relax the numbers.
This is the guidance from ESD TR53 Compliance Verification of ESD Protective Equipment and Materials.
The objective of the periodic test procedures listed in this document is to identify if significant changes in ESD equipment and materials performance have occurred over time.
Test frequency limits are not listed in this document, as each user will need to develop their own set of test frequencies based on the critical nature of those ESD sensitive items handled and the risk of failure for the ESD protective equipment and materials.
Examples of how test frequencies are considered:
Daily wrist strap checks are sufficient in some applications, where in other operations constant wrist strap monitoring may be used for added operator grounding reliability. Packaging checks may depend on the composition of the packaging and its use. Some packaging may have static control properties that deteriorate more quickly with time and use and some packaging may be humidity dependent and may have limited shelf life.
Some materials, such as ESD floor finishes, may require more frequent monitoring because of their lack of permanency. Other materials, such as ESD vinyl floor covering, may require less monitoring. The testing of a floor should also be considered after maintenance on the floor has been performed.”