Load cells answer low-force shortcomings

Edited by the Engineeringtalk editorial team Nov 6, 2006

Load cells are designed for low-force applications such as pumps, contact sensing and variable force control.

Available from Measurement Specialties, FS20 series load cells are designed for low-force applications such as pumps, contact sensing and variable force control.

The FS20 is available for compression forces ranging from 750 to 1500g, providing a 1 to 4V full-scale output and an unprecedented 45N overrange limit.

This device is ideal for medical applications such as body fluid infusion pressure measurement and tube occlusion detection.

The FS20 provides combined linearity, hysteresis and nonrepeatability performance to +/-1% FSO.

Prior to designing the FS20, Measurement Specialties studied how load cells with similar fit and function have failed in the field.

In addition to these studies, Measurement Specialties assessed the entire life cycle costs associated with this product: acquisition, integration and warranty support.

The FS20 was designed at the outset to minimise the life cycle costs associated with products of this type.

Thus, the FS20 offers not only the lowest acquisition cost in its class, but also lower integration and warranty support costs than comparable products.

In infusion pump applications, a thin and flexible disposable isolation diaphragm and cartridge assembly are normally used to isolate the transducer from blood products and/or to maintain drug purity.

These diaphragm/cartridge assemblies are normally replaced with each use.

Because of cartridge and pump manufacturing tolerance variations, the physical thickness and parallelism of the load platform with respect to the instrument base become critical parameters that directly influence the costs of integrating any sensor into infusion pump systems.

Unlike competitive designs which use a pressure capsule embedded within a silicone gel-filled cavity, the FS20 measures direct force.

This enables tight control of device thickness and platform parallelism with respect to the instrument base, as compared with gel-filled models, eliminating the need to shim the sensor within the pump assembly.

The FS20 is not subject to lead-wire fatigue common with competing designs.

Furthermore, the FS20 is designed to be insensitive to small angle or positional variations relative to the replaceable isolation diaphragm due to normal manufacturing tolerances, making it ideal for high volume OEM manufacturing.

The FS20 is built with Microfused technology in which micro-machined silicon piezoresistive strain gauges are fused with high temperature glass to a high performance stainless steel flexure.

This process eliminates age-sensitive organic exposes used in traditional load cell designs and provides excellent long term span and zero stability.

Operating at exceedingly low strains, Microfused technology provides gauge factors greater than 100, superior resolution, high overrange margins and essentially unlimited life cycle expectancy.

Microfused load cells have been tested extensively, and in every case, the test fixtures have always failed before the load cells.

Microfused technology has demonstrated unprecedented reliability and long-term stability in critical safety systems such as automotive stability control as well as in common products like bathroom scales and paint sprayers.