Measure that load

Traditional load cells are typically made from strain gauges which output a 20 mV total change in signal in response to applied loads.

A user would need a signal conditioner to condition this signal, a data acquisition system to digitise the signal and application software to view and process the signal!

But now, Mountain View, California-based Loadstar Sensors has come up with a more elegant and simpler solution!

Its iLoad Digital USB sensors convert a load into a reading on a PC without need for any additional signal conditioners, data acquisition systems or special software. So all you need to do is to connect one of the company's iLoad Digital USB sensors to a PC's USB port and start measuring. The company's optional LoadVUE Lite software can provide an interface to make it even more convenient to measure loads.

The sensors are designed for applications that need to input a signal directly into an existing PLC/DAQ - there is no need for a signal conditioner or lineariser. The iLoad Analog sensors convert a load into a signal in the 0-5 VDC range - they output a linear signal: 0.5V at no load and 4.5V at full load.

The sensors themselves are essentially parallel plate capacitors. And the distance between the plates of the capacitors is varied when a user applies a load. Since the amount of charge stored is directly proportional to the area between the two plates and inversely proportional to the distance between the plates, if the plates are separated by a spring, upon application of a force, the distance between the plates is reduced by the amount of spring deflection. This deflection leads to a change in capacitance, which can be calibrated and used to deduce unknown loads.

Capacitance, however, cannot be easily carried over long distances; it is prone to errors from adjacent electromagnetic fields and losses in the wiring system. This is a key reason why capacitance may not have been used widely until now.

But the designers at Loadstar Systems got round the problem by converting the raw capacitance to a digital signal. The digital signal is then processed to eliminate noise, converted into a signal in the 0-5 VDC range, and output to the USB port.

For its efforts, the company recently received the Frost & Sullivan 2007 North American Product Innovation of the Year Award.