MEDICAL SENSORS / WHITE PAPER
Sensors for Medical Pump Applications
PAGE 4
The FC22 miniature force sensor is based on the
same operating principle; however, the working
area is smaller to facilitate point load measurement.
The cell's form factor and cable connection offer
different integration options. The FC22 cell is
also available in a millivolt bridge version.
The FX1901 RoHS compliant compression sensor is
used, for example, in physical therapy, to measure
patient weight (scales), and in chiropractic and
exercise equipment. Five measurement ranges
span maximum loads from 10 lbf to up to 200 lbf
(approximately 5kg to 100kg). The analog output
signal relative to the input voltage is 20mV/V (20mV
of output for every 1V of input voltage). This 1%
accuracy load cell is based on a cost-effective design.
The FX29 is the latest innovative load cell product
from TE and offers several new and improved features
and due to many design changes, will be available
at a significantly lower cost than previous load cell
models. The FX29 is a miniature compression load
cell designed for embedded force measurement
applications. The sensor incorporates the high-reliability
Microfuse technology for the force elements and is
offered in ranges from 10lbf to 100lbf. The FX29 has
expanded the types of output types that are available
and includes mV, amplified and digital output options.
The incorporation of digital circuitry provides greater
overall system accuracy and the low measurement
ranges available allow for its use in a broader range of
applications. High over-range protection safeguards
the sensor from surges and spikes in the system and
the low deflection with high output sensitivity means
less stress on the sensing diaphragm which makes
the FX29 ideal for demanding medical applications.
Force Sensor Product Examples
Some product examples are given to illustrate the
principles of operation: In the FS20 force sensor, a disc-
shaped load collector at the top of the cell is exposed
to the mechanical stress caused by the fluid pressure in
the pump. The metal load collector acts as a working
point. It is deflected about 0.05 millimeters at rated load.
A silicon Piezoresistive strain gage is fixed underneath
the load collector. When the strain gage is exposed
to stress by the elastic bending of the load collector,
the resistance of the strain gage structure changes.
This change is processed in an integrated circuit (IC)
and is fed forward to the output lead. Zero and span
of the cell are normalized to ensure interchangeability
of the sensor. Miniature force sensors of the FS20
type offer a particularly attractive combination
of electromechanical and economic features.
The RoHS compliant FS20 cell is available in two
versions with either up to 750 grams of force or with up
to 1500 g of force range. A high-level output, low noise,
low off-center errors, and high overrange capability (up
to 2.5x) in combination with fast and accurate results
(± 1 % of span) plus temperature compensation for a
range between 0° C and 50° C make the cell an excellent
choice for pump monitoring. As the load collector
deflection is very small, the cell has an essentially
unlimited cycle life expectancy. The cell's compact
design (25.1 x 17.27 x 8.26 mm) allows for use in a broad
range of applications with space constraints such as
infusion pumps and other portable medical applications.
FC22 FS20
FX29 FX1901
OPERATING PRINCIPLE OF A COMPRESSION LOAD CELL
WITH PIEZORESISTIVE STRAIN GAGES
