Issue link: https://www.e-digitaleditions.com/i/1371139
32 May/June 2021 Tablets & Capsules beds. The plastic-to-plastic contact eventually leads to a static discharge. Understanding that tablet press and packaging rooms require strict environmental and process controls, sev- eral simple changes can help to minimize electrostatic buildup. While every strategy outlined may not be suit- able for your application, consider these simple steps: • Increase the relative humidity—Moisture deters static, so increasing the room's relative humidity slightly will reduce static discharge. • Ground the detector—Ensuring that a ground wire from the metal detector frame is attached to an earth ground will prevent electrostatic buildup. • Use a deionizing or static bar or anti-static blow- ers—Today's systems provide high performance with versatility and simple installation. • Use an alternative plastic such as Tivar for metal detector chutes and conveyor-system slider beds— Tivar is a proprietary ultra-high-molecular-weight polyethylene that has antistatic properties and is suitable for direct product contact. If you cannot implement these suggestions, some metal detectors, such as the Eriez Xtreme, have a special mode for high-static applications. This mode uses an algorithm that identifies the unipolar signal of static, ignores it, and drastically reduces its impact during operation. However, we strongly recommend first employing the static- dissipating strategies previously outlined where possible. Electrical interference. Electrical interference (or noise) from surrounding equipment or the main electrical supply can also impact a metal detector's signal, and at sufficient levels, such ambient noise will cause false trips. Accordingly, a metal detector's power wiring should be run in a dedicated conduit. The best insurance against electrical noise and false trips is to run a separate circuit to the metal detector from the main power bus. This circuit should be free of all loads except the metal detector. If this is impractical, you can often obtain reliable operation in green) that are wound equidistant from the transmitter coil. The transmitter emits a signal to the receiver coils and creates a balanced electromagnetic field. The generated signal has two primary constituents: phase (angle) and amplitude (strength). The signal's amplitude has two components: width and length. Most state-of-the-art metal detectors use a boundary for detec- tion. For example, in Figure 2, the detection boundary is shown as a green rectangle on the detector's full-color human-machine interface (HMI). If a sufficient amount of metal passes through the detector, it will disrupt the signal's balanced state by penetrating the established boundary, and a detection (or trip) will occur. Metal detectors fail to perform adequately for three main reasons: the detector installation is suboptimal, the detector isn't working properly, or the orientation effect is allowing metal to pass undetected. Suboptimal installation Suboptimal installation can allow environmental fac- tors such as static electricity, electrical interference, and excessive vibration to impact the detector signal's stabil- ity, which may mask metal passing through the detector or cause false trips. Let's take a closer look at each of these environmental factors and how to minimize their effects. Static electricity. Minimizing electrostatic buildup in a metal detector is critical because an electrostatic dis- charge can cause a false trip or possibly even damage the detector's electronics. Since a metal detector chute is plastic, static buildup often occurs when a detector is placed at the discharge outlet of a tablet press. In such cases, as false trips increase, the operator's level of confi- dence in the detector decreases. This can lead operators to desensitize or even shut off the detector. Static buildup also occurs on metal detector conveyor systems installed on packaging lines because metal detec- tor manufacturers use plastic belting with plastic slider Figure 1 Metal detector coil Transmitter coil Receiver coil 1 (+) Receiver coil 2 (-) Metal detector shell Figure 2 Metal detector full-color HMI A trip occurs when the established boundary has been penetrated. Boundary