DESIGN
Sensing Progress
High-voltage, optical, position and current sensor
assemblies support the precision, stability and
reliability requirements of medical equipment.
S. Oxley, R. Cronan, D. Winkler, M. Torres
TT electronics plc
TT electronics Components Group
Enabling technologies
The medical technology industry thrives
on innovation. Not only are medtech
manufacturers on a constant quest for
next-generation devices that push the
boundaries of what technology can do,
but they are equally driven to develop
products that give physicians the means to
provide precise, reliable diagnostics and
reduce the need for invasive exploratory
surgery. Developments in sensing technology, such as high-voltage, optical, position
and current sense devices, help to enable
these advances, especially in the diagnostic, imaging, laboratory, patient care, and
medical instrument areas.
High-voltage sensing
Medical systems present a range of high-voltage sensing requirements from the 5
kV level used for defibrillation to 70 kV for
X-ray generation. It is important to control these voltage levels to a high degree of
accuracy and stability. The accuracy and
stability depends on the characteristics of
a high-ratio resistive voltage divider, which
can sample the high voltage and feed back
a proportional control signal at a voltage
level compatible with ADC inputs. But
there are other characteristics beyond the
voltage rating that are critical for medical
applications.
For example, portable defibrillators
require a physically small part because
of the compact size of the finished unit.
Also, the device deploys in a wide range of
environments with uncontrolled climates,
so resistance to high humidity is essential.
Since defibrillation dose control is subject
to a tight error budget, resistive sensors
must have excellent linearity, expressed by
voltage coefficient (VCR) and temperature
coefficient (TCR), and long-term stability
under voltage stress. Finally, the quality
and reliability levels associated with emer-
gency medical equipment are essential. The
use of high-voltage chip and planar resis-
tors has enabled several types of automated
external defibrillators to meet this combi-
nation of requirements.
Optical sensing
Optical sensors and LEDs offer reliable
and cost-effective sensing technologies
for increasingly complex medical devices.
Along with the ability to sense position
or object placement at very high resolution, optical switches are a “touchless
sensing” device and have a reliability
advantage over other technologies because
the device’s lifetime is independent of
its mechanical usage. Self-calibration
modules are available to enhance sensor
capabilities or to help the user design an
effective interface solution for the device.
Examples of medical equipment using
optical sensors include defibrillators;
modular infusion and monitoring systems;
electronic ambulatory devices; infusion
pumps for hospitals; fluid management
pumps; angiographic monitors; urinalysis
devices; automated specimen handlers;
secure drug dispensing systems; anaesthesia dispensing stations; blood, gas
and electrolyte analysis systems; patient
oximetry probes; glucose monitors; electronic scalpels; light therapy lamps and
