Critical Fluid Management in medical applications requires precise, repeatable, and reliable measurements. Strain Measurement Devices is a leading sensor manufacturer covering a vast array of measurement systems. There’s an important need for sensors that alert any critical interruption in infusion, insulin, enteral feed pumps, or wound irrigation systems. An occlusion sensor with thin-film precision is ideal, used to avoid any disastrous consequences by notifying the operator of anything wrong, like a pinched tube or pump failure. Custom Occlusion Sensors

Engineers utilize tube sensors to monitor pressure in pump systems that measure the force exerted onto a sensor pressed against any expanding walls of a polyurethane or PVC tubing. Sensors can also be placed behind the pump to record pressures as the pump backs up against the sensor during operation. Thin-film sensors have the ability to survive harsh environments and feature the accuracy required to be successful in critical applications. 

For over 20 years Strain Measurement Devices has been using the state-of-the-art thin film vacuum deposition process to bond strain gauges directly to a number of materials. Thin film sensors are built without organic materials so that they are not hydrophilic, aged and fully oxidized. Over time, the thin film strain gauge has proven itself to be the preferred means for measuring strain in critical applications where small size, robust performance, long-term stability, and superior accuracy are required.

SMD Sensors Application Solutions

Noninvasive Tube Pressure Sensor for Occlusion Detection

A miniature force sensor can be used, mounted into a housing component and closed into a tube. The load-button of the sensor presses against the tube wall and when any expansion is detected in the tube, the sensor measures pressure changes. Strain Measurement Devices has developed a test that characterizes a tube sample so that the most appropriate force sensor range and the optimum pre-compression can be applied to the tube. Accuracy achievable by this technique is approximately +/-15% across a range of different tube materials or +/-5% for a single tube material.

Silicone tubing gives the best results from this approach, as it has low creep over time, but techniques can also be applied to deal with situations where the chosen tube material shows a stronger tendency to creep. 


Precision Non-Invasive Pressure Sensor for Flow Measurement Application

This approach is for when a higher degree of accuracy is required, more than what can be obtained by a sensor directly applied to a tube wall. A disposable set with a molded membrane is an ideal solution, the sensor contacts the membrane via a flat plate. The sensor acts as a pressure-summing element. Due to the small full range deflection of the sensor, movement of the membrane is minimized, resulting in good linearity characteristics. In this particular case, the full range of the sensor is 1000 mbar, with an accuracy of +/-1 mbar. The example illustrated has a 0.5” diameter load surface.