Flexible Resistor Provides Flow Measurement

Compared to a potentiometer, a film resistor, whose value changes are based on the amount of deflection, has considerably fewer parts and other desirable characteristics. Working with Flexpoint Sensor Systems, Precision Pumping Systems has determined a flexible sensing technique can be used in a flow meter to provide a direct inferential reading of flow rate without incurring any significant pressure drop. The technique does not use rotating components that could easily fail and is reasonably priced.

Flexpoint Sensor Systems' Bend Sensor is a single-layer flexible material that changes resistance based on deflection. As a result, it can accurately measure movement or flow in multiple directions. A layer of the material coated on a substrate produces a sensor, and the material can be applied to uneven, angled or curved surfaces.

Design concerns for an insertion meter that goes in the flow stream include sensitivity, fluctuation/flutter and durability. However, sensitivity is not a problem. It does not take a lot to bend the sensor and it's extremely sensitive. Experiments with airflow indicate the sensor has potential applications in heating, air conditioning and ventilating — applications that produce much lower forces on the movable structure.

The biggest problem in water flow is flow-induced flutter. “If you put these sensors into large pipes where the flow is great, like an 8-inch pipe, the biggest problem we have is flutter,” says David Beck, director of engineering, Flexpoint Sensor Systems. The sensor reacts so quickly and easily that flutter can be detected. To smooth out the motion, the flow sensor design has a mechanical structure that surrounds the sensor.

With regard to durability, life cycle testing has been performed on the Bend Sensor material for a million cycles. The sensors were bent around a 25-inch radius rod at two cycles per second. In fact, sensors have been tested to over 35 million cycles without failure. The sensor's material makes it applicable for most harsh environments.

	Compared to a potentiometer, Flexpoint Sensor Systems' Bend Sensor has the edge on fewer parts. The flexibility of the base material determines the amount of deflection of the film layer and the change in resistance. The appropriate base material allows the development of an application-specific sensor for insertion flow meters.