Biomedical Engineering Reference
In-Depth Information
Sensor
Calibration
Analog
Processing
A/D
Control &
Feedback
Signal
Processing
Data
Storage
Output
Display
Data
Transmission
FIGURE 9.2
Basic instrumentation systems using sensors to measure a signal with data acquisition, storage,
and display capabilities, along with control and feedback.
later in this chapter. Once the analog signals have been digitized and converted to a form
that can be stored and processed by digital computers, many more methods of signal
conditioning can be applied (for details, see Chapter 11).
Basic instrumentation systems also include output display devices that enable human
operators to view the signal in a format that is easy to understand. These displays may
be numerical or graphical, discrete or continuous, and permanent or temporary. Most out-
put display devices are intended to be observed visually, but some also provide audible
output—for example, a beeping sound with each heartbeat.
In addition to displaying data, many instrumentation systems have the capability of stor-
ing data. In some devices, the signal is stored briefly so further processing can take place or
so an operator can examine the data. In other cases, the signals are stored permanently so
different signal processing schemes can be applied at a later time. Holter monitors, for
example, acquire 24 hours of ECG data that is later processed to determine arrhythmic
activity and other important diagnostic characteristics.
With the invention of the telephone and now with the Internet, signals can be acquired
with a device in one location, perhaps in a patient's home, and transmitted to another
device for processing and/or storage. This has made it possible, for example, to provide
quick diagnostic feedback if a patient has an unusual heart rhythm while at home. It has
also allowed medical facilities in rural areas to transmit diagnostic images to tertiary care
hospitals so that specialized physicians can help general practitioners arrive at more accu-
rate diagnoses.
Two other components play important roles in instrumentation systems. The first is
the calibration signal. A signal with known amplitude and frequency content is applied
to the instrumentation system at the sensor's input. The calibration signal allows the
