Force Sensor Adapter

Thought Technology Ltd, Canada
Model: T9540
  • The force adapter connects to third party Force sensors of varying sensitivity to measure pressure or force, such as Tekscan,Flexiforce and Imaging Technologies Uniforce.
  • It can be used to monitor tactile activity, or as a foot switch for Gait Analysis.

PRODUCT OVERVIEW

Force AdapterSensor GraphThis adapter connects to third party Force sensors of varying sensitivity to measure pressure or force, such as Tekscan Flexiforce and Imaging Technologies Uniforce. It can be used to monitor tactile activity, or as a foot switch for Gait Analysis.

OPERATING PRINCIPLE

A force sensor is sensitive to load applied to a small area of its surface. Force sensors are available in a number of maximum load ratings, for example 10lbs and 50lbs. When connected to a person or object they sense changes in the applied pressure. The sensor plugs into the adapter which in turn plugs into the encoder.

Recommended Sensors

TECHNICAL SPECIFICATIONS

  • Length : ~152cm (60”)
  • Weight (approx.) : ~10g
  • Recommended Force Sensors : Manufacturer – Tekscan Inc
    • Sensor model – Flexiforce Sensor
    • Part # A201-1 (1lb)
    • Part # A201-25 (25lb)
    • Part # A201-100 (100lb)
  • Force Sensor Type : Variable Resistive
  • Force Sensor Resistive Range (Rfs) : 1KΩ – 1.4MΩ (native Infiniti modes)
  • Output Voltage Transfer Function : Vout = [301KΩ/(Rfs +575KΩ)] * Vs where Rfs is the resistance of force sensor in KΩ and Vs is sensor supply voltage.
  • Supply Voltage : 7.26VDC nominal
  • Current Consumption : < 1mA @ 7.26 VDC nominal
  • Accuracy : ±1%

This sensor provides a relative measurement of applied pressure. The output voltage signal may be converted to pressure units (PU) for qualitative purposes only. The measured signal does not accurately reflect applied pressure at the sensing component.

INTERFACING WITH 3RD PARTY DATA ACQUISITION SYSTEMS

Recommended Connectivity for Electrical Safety

Thought Technology recommends the use of TT Sensor Isolator ST9405AM when interfacing patient connected sensor(s) to line powered equipment(s) or devices.

Ten20The TT Sensor Isolator ST9405AM is an interface device providing medical grade electrical isolation between the patient connected sensors and the acquisition system. It provides the equivalent of Two Means of Patient Protection under IEC 60601-1, and supplies battery power to the sensors. Using this device ensures Thought Technology sensors are safely interfaced to the analog inputs of line-powered systems such as computers with DAQ cards.

Note that this device isolates only between sensors and the DAQ interface, not between different sensor channels.

The TT Sensor Isolator can interface up to 4 sensors to a DAQ card. TT Sensor Isolator can be connected to the DAQ card in two ways:

  • via two stereo jacks, or
  • via a DB-15 connector; a BNC interface cable (SA9409BNC) or a pigtail cable (SA9409PGT) can be provided with the unit.

Graph

For more detailed information on the Sensor Isolator 4∞, consult the Thought Technology Science Division website or contact the sales department or your distributor.
Division website or contact the sales department or your distributor.

Direct Connectivity for Electrically Isolated Systems

The following notes are provided for qualified users to directly interface Thought Technology sensors with external systems.

WARNING: If the sensor is interfaced to non-Thought Technology devices without the use of a TT Sensor Isolator SE9405AM, an elevated risk of electrical shock may be present. In particular, if a patient-connected sensor is connected to any line powered device(s) or equipment(s), it will be the responsibility of the qualified user to ensure the electrical safety in the setup and to ensure that the device or equipment provides sufficient isolation.

To interface with a sensor, a single sensor cable may be cut in half. Both sides can then be used to make custom interfacing cables by stripping the outer insulation of each required conductor. The sensor cable contains 4 color coded conductors. The table below shows the color coding and pin connector assignment.

Pin Color Code Function Note
1 metal (shield) ground Signal and power ground, connection required.
2 yellow auxiliary (sensor ID) No connection required.
3 green signal Sensor output signal
4 red sensor power Supply voltage, +7.26V referenced to ground. Note: sensor performance may be sensitive to supply voltage.

Sensor Graph

Notes:

1. The nominal supply voltage for this sensor is 7.26V. The sensor can safely be used with a supply voltage of up to 9V.

Recommended Specifications for DAQ Hardware

  • Recommended resolution of 0.15mV (16-bit ADC over 10V span) or better
  • Minimum input range:
    • If connected via SE9405AM Sensor Isolator, choose 0-5V (unipolar) or ±5V (bipolar).
    • If directly connected to DAQ, choose ±5V (bipolar).

Simplified Transfer Function

Transfer FunctionConversion of voltage to pressure units (PU)
(for quantitative purposes only)

The simplified transfer function assumes the sensor is used with the Sensor Isolator, or the supply voltage provided in the user setup is 7.26V nominal.