SENSORS FOR MEDICAL
PUMP APPLICATIONS

Sensors for Medical Pump Applications

AS THE NEED FOR MEDICAL ADVANCES INCREASE, SENSINGTECHNOLOGY WILL CONTINUE TO BE THE FOUNDATION TO EVOLVE
THE MEDICAL INDUSTRY INTO A MORE CONNECTED, RELIABLE AND
SAFE OPERATION. ELECTRONIC SYSTEMS IN MEDICAL EQUIPMENT,
DEVICES AND PROBES RELY ON SENSOR SIGNALS AS A BASIS FORCONTROL ACTIVITIES, ACCURATE DIAGNOSIS AND TREATMENT.
Those systems are evolving to include moresophisticated capabilities while maintaining or
improving their reliability. They are becoming moreintuitive to use and there continues to be a pushtowards more mobile and connected medical products.
Additionally, even though the healthcare industry
has been slower to adopt the Internet of Things (IoT)
technologies than other industries, the Internet ofMedical Things (IoMT) is poised to transform how
we keep people safe and healthy especially as thedemand to lower healthcare costs increases.

Because infusion pumps are frequently used toadminister critical fluids, including high-risk medications,pump failures can have significant implications forpatient safety. Many infusion pumps are equipped withsafety features, such as alarms or other operator alertsthat are intended to activate in the event of a problem.
For example, some pumps are designed to alert patientsand staff when air or another blockage is detected in thetubing. Some newer infusion pumps, often called smart
pumps, are designed to alert the user when there is arisk of an adverse drug interaction, or when the user sets
the pump’s parameters outside of specified safety limits.
Within traditional and smart pump applications, sensors
are key components in controlling and monitoring
infusion pumps. They are designed to provide occlusion
detection, monitor fluid flow, provide feedback formotor control and in some instances, sense thetemperature of the IV fluid being administered. The
figure below illustrates the potential locations of
sensors employed in a typical infusion pump.

MONITORING THE FLOW RATE AND/OR POTENTIALOCCLUSION DURING INFUSIONS IS AN APPLICATION FIELD
FOR LOW RANGE COMPRESSION LOAD SENSORS

These trends have increased the overall demand forsensors in medical products and devices, but it isalso pushing those sensors to be smaller, faster, moreaccurate and more reliable. And for most manufacturers,
budgets are limited, meaning low-cost components
are ideal. Therefore, sensor innovations reaching themarket need to feature smaller form factors while
maintaining high functionality and affordability.
Sensors play a critical role in a wide range of medical
functions including various medical pump and flow
applications. An infusion pump is a type of medical
pump device that delivers fluids, such as nutrientsand medications, into a patient’s body in precise andaccurate prescribed volumes over a specified time.
These types of medical pumps are in widespread use
in clinical settings such as hospitals, nursing homes
and in-home settings since they offer significant
advantages over manual administration of fluids. Theseadvantages include the ability to administer very small
doses, confirm programmed volumes and reducing
employee workload due to automated administration.

MEDICAL SENSORS / WHITE PAPER

ILLUSTRATION OF POTENTIAL SENSOR LOCATIONSINCLUDED IN TYPICAL INFUSION PUMP APPLICATIONPAGE 2Sensors for Medical Pump Applications
There are many pump variables that need to beconsidered within medical pump applications. Thesevariables include the volume of fluid but also the modeof infusion, which can be continuous, intermittent or
patient-controlled. To ensure a correct flow of the fluid,force sensors are integrated into the pump to detect
possible occlusions. The force sensor is typically installed
under a portion of the tubing that is carrying the IV
fluid. When a blockage occurs in a pump the tubing
expands. A force sensor placed where the tubing meetsthe housing can detect this expansion by monitoring theforce applied to the sensor by a section of the tubing.
The sensor can trigger an alarm to alert the user if thisexpansion is detected. The same principles of operation
can apply in infusion pumps and devices designed for
operation by medical professionals in settings suchas hospitals, hospices, and home-care. Expansion bymonitoring the force applied to the sensor by a sectionof the tubing. The sensor can trigger an alarm toalert the user if this expansion is detected. The same
principles of operation can apply in infusion pumps anddevices designed for operation by medical professionals
in settings such as hospitals, hospices, and home-care.
Although medical sensors for external use, such as ininfusion pumps, tend to pose less of a technologicalchallenge than implantable sensors, they still mustmeet tough requirements. Even as devices become
smaller for increased portability, users still expect thatthese systems maintain functionality and accuracy.
To design small yet accurate medical devices,component parts such as sensors must also offer
robust features at a low cost. Additionally, reliability
is essential for most medical pump applications,especially where critical fluids are being infused.

Force Sensor Technology andPrinciples of Operation
A force sensor is a sensor whose properties change
when a force, pressure or mechanical stress is applied.
A range of technologies can be utilized in the design
and manufacture of a force sensor. TE Connectivity (TE)designs and manufactures force sensors for applications
that require high performance or unique packaging,including medical devices and equipment. TE’s force
sensors are based on a proprietary Piezoresistive siliconstrain gage (Microfused) technology, that combines
durability and long-term stability in extremely low-costpackages. Force sensors (also referred to as load cells)
are used in a variety of medical applications including
infusion pumps. Other applications in the medical
market include physical therapy, hospital beds (patient
weight), surgical staplers, cardiopulmonary-resuscitation(CPR) assist machines for emergency medical
treatment, as well as for oxygen tank monitoring.

MEDICAL SENSORS / WHITE PAPER

Principles of Operation
The Piezoresistive effect is widely used in sensor
technology. The Piezoresistive effect is a change in theelectrical resistivity of a semiconductor or metal whena mechanical strain is applied. A Piezoresistive force
sensor contains several thin wafers of silicon embedded
between protective surfaces. The surface is connected
to a Wheatstone bridge, a device for detecting small
differences in resistance. The Wheatstone bridge runsa small amount of current through the sensor. Whenthe resistance changes, the current passing throughthe sensor also changes. The Wheatstone bridge
detects this change and reports a change in pressure.

DIAGRAM OF A PIEZOERESISTIVE FORCE SENSOR WITH
A WHEATSTONE BRIDGE AND AMPLIFIER

The proprietary TE Microfused manufacturing
technology is based on micromachining siliconPiezoresistive strain gages and fusing them in ahigh-temperature glass-bonding process to a highperformance stainless-steel substrate. This mature andreliable process has delivered millions of force sensors
and is a proven technology in a wide variety of medical
applications. Microfused technology eliminates agesensitive organic epoxies that are used in traditionalload cell designs, thus providing excellent long-term
span and zero stability. The cells measure force directly
and are therefore not subject to lead-die fatigue
issues common with competitive designs, which use
a pressure capsule embedded within a silicone gelfilled cavity. Operating at very low strains, Microfusedtechnology provides an essentially unlimited cycle life
expectancy, superior resolution, high frequency response
and high over-range capabilities. Overall, Microfusedforce sensors have demonstrated their ruggedness
and reliability in a wide range of medical devices.

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Sensors for Medical Pump Applications

Force Sensor Product Examples
Some product examples are given to illustrate theprinciples of operation: In the FS20 force sensor, a discshaped load collector at the top of the cell is exposedto 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 underneaththe 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 spanof the cell are normalized to ensure interchangeabilityof the sensor. Miniature force sensors of the FS20
type offer a particularly attractive combinationof electromechanical and economic features.

OPERATING PRINCIPLE OF A COMPRESSION LOAD CELL
WITH PIEZORESISTIVE STRAIN GAGESThe 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 (upto 2.5x) in combination with fast and accurate results(± 1 % of span) plus temperature compensation for arange 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 essentiallyunlimited 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.

MEDICAL SENSORS / WHITE PAPER

The FC22 miniature force sensor is based on thesame operating principle; however, the working
area is smaller to facilitate point load measurement.
The cell’s form factor and cable connection offerdifferent integration options. The FC22 cell isalso available in a millivolt bridge version.
The FX1901 RoHS compliant compression sensor isused, for example, in physical therapy, to measurepatient weight (scales), and in chiropractic andexercise 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.

FS20

FC22

FX1901FX29The FX29 is the latest innovative load cell productfrom TE and offers several new and improved featuresand due to many design changes, will be available
at a significantly lower cost than previous load cell
models. The FX29 is a miniature compression loadcell designed for embedded force measurement
applications. The sensor incorporates the high-reliability
Microfuse technology for the force elements and isoffered 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 ofapplications. High over-range protection safeguards
the sensor from surges and spikes in the system andthe low deflection with high output sensitivity means
less stress on the sensing diaphragm which makes
the FX29 ideal for demanding medical applications.

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Sensors for Medical Pump Applications

Bubble Detection in Infusion Pumps
Bubble detection is critical in applications such as infusion pumps, hemodialysis andblood flow monitoring where interruption in performance can be life-threatening.
Ultrasonic bubble detectors are non-contact acoustic bubble and liquid detectors
used to identify air bubbles and liquids in infusion tubes. They are widely used inapplications such as liquid transfer and infusion in medical pumps, pharmaceuticals,
industrial and scientific research. TE’s AD-101 air bubble detector for non-invasive,
continuous monitoring of fluid for air bubble detection, uses ultrasonic technology
to positively identify the presence of a break in flow of any type of liquid. With
continuous self-diagnosis and flexibility in packaging, these sensors provide reliable
and accurate bubble detection for critical applications such as infusion pumps.

AD-101 AIR BUBBLE DETECTOR

Bubble Detection Technology
As shown below, an air bubble detector such as TE’s AD-101, is designed to be installed directly onto the tubingthat is used to infuse the liquid into the patient. The bubble detector contains an embedded piezo transducer thatemits a tone burst ultrasonic signal. The signal passes through the tubing and it’s contents. A piezo receiver listens
for the ultrasonic signal. Liquids transmit ultrasound efficiently, so a strong signal passes when only liquid is present
in the tubing. Air bubbles do not transmit ultrasound waves efficiently, so the signal is weakened by any bubble in
the liquid. An internal circuit measures the amplitude of the receiver signal and provides the appropriate output.
The ultrasonic air bubble detector is non-invasive and has no direct contact with the liquid.
The AD-101 can handle tube sizes from 3mm to 10mm and can be custom-designed to fit
unusual tube sizes. The response time is less than 2ms, provides a 3.3V TTL output logic level
and has an integrated LED that provides a visual indication if a bubble is detected.
The AD-101 also has a built-in self-diagnostic capability that continuously monitors theoperation of the sensor. The sensor can be operated in any position with liquid flowing upward,
downward, or at any angle. Gravity has no effect on the detection capability.

ULTRASONIC AIR BUBBLE DETECTOR - HOW IT WORKS

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Sensors for Medical Pump Applications

Other Sensors in Infusion Pumps
The designs for infusion pumps are becoming more sophisticated and additional features and diagnostics arebeing added. This will require the use of additional sensors as well as sensors with improved performance.
Two other areas in medical pumps where sensors have been utilized include position sensors for motor
feedback and diagnostics and temperature sensors for the monitoring and control of infusion liquids.
Anisotropic Magnetoresistive (AMR) position sensors are precise and contact-less devices that measure
the changes in the angle of a magnetic field as seen by the sensor. TE’s magnetic sensors offer robust noncontact position measurements in harsh environments. For example, the unique features of the AMR effectallow the measurement of sub-micrometer displacements in precision linear encoders. The AMR technology
is also successfully used for presence detection, such as the endpoint detection in pneumatic cylinders. ThisAMR technology provides a low-cost, robust technology for monitoring either linear or rotary motion andallows precise position feedback for a range of motors that drive most infusion pumps. These durable products
are designed to provide enhanced output accuracy for smooth motor control and their small size often
reduces replacement costs and allows for design into many compact, automated, lower-cost assemblies.
On the temperature sensor side, it has been shown that intraoperative
intravenous fluid administration and blood product transfusion have considerable
effects on body temperature. Thus, it is important to monitor and control
the temperature of fluids. A range of medical fluid warmers are often utilized
when fluids are infused intravenously, and temperature sensors are integrated
as part of these systems to monitor and control the temperature of the fluid.
While many of the warming units are separate and external to the infusion
pump, there is a push to integrate this option into new infusion pump designs.
TE Connectivity designs and manufactures a wide range of temperaturecomponents and assemblies that have been used in a broad range of invasive
and non-invasive medical applications to monitor everything from core bodytemperature to the temperature of cryogenic gases used for angioplasty balloons.

MEDICAL TEMPERATURESENSOR ASSEMBLIES

Summary
TE designs and manufactures a broad range of sensors utilizing many different technologies thatare critical for the monitoring and control of electronic systems for a range of applications in
the medical field. One of the major areas within patient treatment is medical pumps and, more
specifically, infusion pumps. TE sensors are applied in the following areas of infusion pumps:• Force sensors to detect occlusions to confirm there is no blockagein the tube that delivers medication to the patient.
• Air bubble detectors are capable of positively identifying the presence of a break in flow of any type of liquid.
• Anisotropic magnetoresistive (AMR) position sensors monitor the
angular or linear position of medical pump motors.
• Temperature sensors are used to monitor and control the temperature ofinfused liquids that are being delivered into a patient’s body.

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Sensors for Medical Pump Applications

Application Fields for Force Sensing
Medical device OEMs are seeking products that provide reliability, appropriate size (miniaturization), lower
cost, and better overall performance. The many medical application areas of force sensing include:• Ambulatory drug dispensing systems, many of which rely on force sensing
as the primary sensor technology for feedback control.
• Surgical procedures are also rapidly improving, as low cost, high reliability force/torquesensing enables precise measurement. Staple machines and ocular surgery devices are being
equipped with force sensors to enable quicker, more precise surgical procedures..
• Pumps used to irrigate and saline-flush sites for knee and shoulder surgeries
increasingly use force sensing to optimize flow rate.
• Load cells are now widely used in saline drip weight measurement.

Applications for Bubble Detectors
Bubble detection is critical in applications such as infusion pumps, hemodialysis
and blood flow monitoring. TE’s AD-101 air bubble detector offers:• Self-diagnostic functions including
power-on and continuous self-diagnosis• Flexibility to be customized to fit any
tube or pipe
• Integral electronics enabling compact product design with easy integration• 20 years of proven performance with sensors sold around the world

TE designs and manufactures sensors for wide variety of medical applications. TE offers ISO 13485 certification
and FDA registration for various sensors and assemblies. Our global network of engineers provides application
specific sensor design, from product concept through manufacturing. TE’ s dedicated medical sensor team offer
rapid prototyping for fast paced product development and offer support throughout the product’ s lifecycle.

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Sensors for Medical Pump Applications

About TE Connectivity
TE Connectivity (TE) is a global technology leader, providing sensors and connectivity essential in today’s
increasingly connected world. We are one of the largest sensor companies in the world with solutions thatare vital to the next generation of data-driven technology. TE’s portfolio of intelligent, efficient and highperforming sensor solutions are used for customers across several industries, from automotive, industrial andcommercial transportation and aerospace and defense, to medical solutions and consumer applications.

AuthorDevin Brock
Manager, Product Knowledge and Training, TE Connectivity Sensors

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