当干扰超过阈值时（在校准期间已经预定）时，受污染的产品是“被拒绝的”（完全自动排斥或在生产线的停止之后）。阈值的确定是关键阶段：实际上，最低阈值可能出现最佳解决方案，但这通常是过量的被拒绝的包装的原因，因为金属检测器检测到最微小的金属颗粒，如此用于打印标签的墨水。最后一代金属探测器使用变频发生器，最佳地适应所产生的信号到测试产品的电磁特性。金属探测器检测铁（Fe），有色金属（NFE）金属和不锈钢（SS）。黑色物体的位置更容易;有色金属是非磁性金属（如黄铜，铝或铜）几乎与黑色金属一样易于检测。不锈钢（其中最常见的类型是AISI304和AISI316）不是磁性的并且具有低的电导率，因此它们是迄今为止最多的群体来检测的金属。一些最新的发展（通过基于Modena的公司Co-El提供的礼貌查看图像）在非常高的频率下运行，并且可以检测到黑色金属和有色金属。不同金属的小球体和CETIFIED直径可用于测试已安装的金属检测器的灵敏度。 Metal detector sensitivity can be affected by many factors, as: type of product (dry, humid, wet, frozen, etc.); product size; product variability; head aperture; environmental conditions (vibrations, electric and electro-magnetic disturbances, disturbances in the conveying system); correct use by the operator (training); user-friendly interface; reliable control and management software; automatic product identifi cation; variable frequency (from 40 to 70 frequencies); DSP technology (digital signal processing); IP69 protection (in humid environments); head with self-diagnostic function; The food industry mainly implements in-line metal detectors (i.e. installed on the conveyor belt); the assembly can include also automatic rejection unit with wastes collecting drawer and a variety of alarms and signal lights. Metal detectors can be combined also with checkweighers. Powder or granulate products and bulk material can be checked by means of free-fall gravity metal detectors, for mechanical or pneumatic conveying systems. In these devices, the product passes through the detecting head and, if contaminated, the rejection system deviates it to a rejection line. There are different apertures for product passage, as well as “Slim Line” confi gurations for applications in limited spaces. Pipeline metal detectors are used to inspect a variety of food products that travel through process pipelines.
金属碎片在肉类加工行业的起源
必须特别注意肉类部门;肉类的高湿度，加上其复杂的质地(水、脂肪和蛋白质)和输送带上的产品数量的变化，使得金属异物的检测极其困难。在这个领域，金属异物的危险是非常高的(与人们可能认为的相反)，这是由于各种原因，其中一些不是很明显，例如:农场里的动物用来自不同来源的复合饲料产品喂养，长时间不咀嚼;因此，它们吞食饲料和农场围栏中出现的金属物体，如链条、金属丝等，并不罕见。通常这些金属物体不会被排出体外，而是留在动物的肠胃器官中，直到宰杀。•牛肉、马肉、猪肉、牛肉:用于注射药物的针头可能会断裂并留在组织中;如果养殖者在将动物送到屠宰线上时没有发出信号，针头碎片肯定会进入牛排;同样的情况也会发生在破损或被遗忘的手术刀上，这些手术刀用于对动物(主要是猪肉)进行消毒，这些动物被生长中的动物围起来，最后变成了熏肉;•加工和未加工的各种产品:除了来自农场的危险之外，我们不应该忘记来自工业加工的危险，包括屠宰线:由于振动，从加工机器上松开的螺母和螺栓; objects coming from on-site emergency maintenance; pins of order sheets (which should be banished from the processing area), etc. Speaking of meat, the most involved products certainly are ground meat and its derivatives, that is sausages, hamburgers, skewers, “ready to cook” products, etc., because they are potentially susceptible of a variety of contamination sources.
