SETRA Mass Monitor
MODEL: 408112 2500g x .005g
The MM410 Series consists of a moment-insensitive load cell module prepackaged with flexures. The load cell module is available in any weighing capacity from 200 grams to 50 kilograms delivering weight measurements accurate to 10 ppm. The Mass Monitor is provided with a circuit designed to linearize and temperature compensate the raw digital signal output of the load cell module. The circuit includes a display connector and a three wire RS232C serial data interface. This interface enables bi-directional communications with the controlling or indicating device. Neither hardware nor software handshaking is required.
The ceramic weight sensor is mounted on a rectangular cast aluminum foundation. Combined with flexures, quartz inductor, positive overload safety stop, desiccant and the oscillator circuit board, the entire module is neatly encased under a formed aluminum cover. This self contained load cell can easily be installed in a scale base or other weight-supporting structure, using only three bolts. A user-built weighing platform can be attached via a threaded shaft that protrudes through the module cover (on high capacity modules, four shafts are provided.)
A display board using a six-digit LCD or a five-digit LED is available and may be used as an integral part of the MM410 package or for testing purposes only.
Principle of Operation
Setra's Mass Monitor consists of a ceramic sensor to which two gold plated electrodes are thermally fused. Doubling as a variable capacitor, the sensor is wired into an LC oscillating circuit which typically operates at well over 5 megahertz. This circuit includes a quartz constant value inductor which can withstand moderate fluctuations in environmental conditions such as temperature and humidity. The inductor's stability makes oscillating frequency entirely dependent upon deflection of the sensor. As weight is applied to the sensor, the gap between the electrodes changes, altering the electrical capacitance of the sensor and changing the oscillating frequency. A microprocessor measures oscillation in the circuit, compensates for temperature-induced variations, linearizes the signal, and provides a digital weight output. The resulting high resolution, coupled with the unique elastic properties of the high grade ceramic sensor provide a weighing accuracy that is ten times better than that of a typical scale using strain gauge load cell technology.