In some industrial processes, it is necessary to sense the condition of a system at one location and, depending on that condition, activate an operation at a location far from that location. For example, in a manufacturing environment, when the count of the finished parts exceeds some value, as sensed in the storage area, a milling machine could be shut down or started. A proximity switch could be used for sensing and a networked (e.g., Ethernet-based) control system could be used for process control. Since activation of the remote process usually requires a current that is larger than the rated load of a proximity switch, one would have to use a relay circuit, which is operated by the proximity switch. One such arrangement is shown in Figure P6.12. Note that the relay circuit can be used to operate a device such as a valve, a motor, a pump, or a heavy-duty switch. Discuss an application of the arrangement shown in Figure P6.12 in the food-packaging industry. A mutualinduction proximity sensor with the following ratings is used in this application:

Sensor diameter = 1 cm

Sensing distance (proximity) = 1 mm

Supply to primary winding = 110 ac at 60 Hz

FIGURE P6.12

Load current rating (in secondary) = 200 mA

Discuss the limitations of this proximity sensor