FlexiForce user manual

02/05/09 FlexiForce Sensor User Manual (Rev G) 8
OVERVIEW
This section outlines Sensor Construction and Application.
FLEXIFORCE SENSORS
The FlexiForce sensor is an ultra-thin and flexible printed circuit, which can be easily integrated
into most applications. With its paper-thin construction, flexibility and force measurement
ability, the FlexiForce force sensor can measure force between almost any two surfaces and is
durable enough to stand up to most environments. FlexiForce has better force sensing
properties, linearity, hysteresis, drift, and temperature sensitivity than any other thin-film force
sensors. The "active sensing area" is a 0.375” diameter circle at the end of the sensor.
The sensors are constructed of two layers of substrate. This substrate is composed of polyester
film (or Polyimide in the case of the High-Temperature Sensors). On each layer, a conductive
material (silver) is applied, followed by a layer of pressure-sensitive ink. Adhesive is then used
to laminate the two layers of substrate together to form the sensor. The silver circle on top of the
pressure-sensitive ink defines the “active sensing area.” Silver extends from the sensing area to
the connectors at the other end of the sensor, forming the conductive leads.
FlexiForce sensors are terminated with a solderable male square pin connector, which allows
them to be incorporated into a circuit. The two outer pins of the connector are active and the
center pin is inactive. The length of the sensors can be trimmed by Tekscan to predefined lengths
of 2”, 4” and 6” or can be trimmed by the customer. If the customer trims the sensor, a new
connector must be attached. This can be accomplished by purchasing staked pin connectors and a
crimping tool. A conductive epoxy can also be used to adhere small wires to each conductor.
The sensor acts as a variable resistor in an electrical circuit. When the sensor is unloaded, its
resistance is very high (greater than 5 Meg-ohm); when a force is applied to the sensor, the
resistance decreases. Connecting an ohmmeter to the outer two pins of the sensor connector and
applying a force to the sensing area can read the change in resistance.
Sensors should be stored at temperatures in the range of 15°F (-9°C) to 165°F (74°C)
Standard FlexiForce Sensors
The Standard A201 sensor is available in the following force ranges:
• Sensor A201-1 (0-1 lb. force range)
• Sensor A201-25 (0-25 lb. force range)
• Sensor A201-100 (0-100 lb. force range)*
* In order to measure forces above 100 lbs. (up to 1000 lbs), apply a lower drive voltage and
reduce the resistance of the feedback resistor (1k
Ω min.). See the sample drive circuit below.