Exposed goods or exhibits can be watched in different ways. An unobtrusive way is to watch the weight of an item and to detect its lifting up from a pad. The measured weight changes and an alarm can be triggered.
The above principle is used in device called TE485PK we have developed. The reference weight can be easily set using just two buttons on the side of the device. When a significant weight change is detected, TE485PK sends an automated RS485 message to the controlling system.
The device measures the weight several times per second so the response to the manipulation of an item is immediate. Follow-up action of the controlling system can be triggering an alarm, warning message for staff, automatic focus of cameras at a particular location, etc.
The principle of operation is suitable for hidden guarding of goods or exposed exhibits. Weight measurement is carried out by a strain gauge. The strain gauge doesn't have to be very accurate – only a significant difference of weight change is detected. It also depends on the particular type of goods or exhibit being watched.