Come on experts, I need answers 
Sorry kconf I was asleep when you posted! 
BRCGS does not require annual calibration/certification for metal detectors, I would refer to the manufacturer’s recommendations.
See BRCGS Global Standard for Food Safety Issue 9 Clause 4.10.3.3 Documented metal detector and X-ray procedures - Guidance:
‘The set-up and design of the operating procedures will need to consider a number of factors, which will affect the sensitivity of the detector and the effectiveness of the rejection mechanisms, including, for example:
• size and type of product – product size and composition can affect the sensitivity of the detector and therefore its ability to identify
• product packaging – product is normally tested in pack, but certain types of packaging will prevent this
• line operating speeds – there must be sufficient time for the detector to identify the presence of a contaminant and the rejection mechanism to accurately and consistently remove the implicated pack from the product flow
• location of the detector – should be risk-assessed to ensure that the placement efficiently and effectively minimises the risk of foreign bodies in the finished product
• customer-specific requirements – some customers have specific requirements relating to detector sensitivity or frequency of tests
• identification of the least sensitive (sometimes referred to as the weakest) part of the detector, to ensure that any contaminated product will still be rejected, even if the contaminant is located at this weakest point.’
'The frequency of testing must be based on the quantity and type(s) of product. However, the following should be considered: ..... blah, blah etc.'
‘The Standard does not require routine calibration of metal detectors beyond the verification/checking activities described in this section. However, planned maintenance or servicing may have value depending on the machine, the manufacturer’s specification, the contract and/or the operating environment.’
Kind regards,
Tony
