You cannot control what you cannot measure, goes an old engineering saw. The measurement reference is accomplished by sensors.
Sensors are available to measure a variety of parameters:
- Acceleration and vibration
- Acoustic and ultrasonic waves
- Chemicals and gases
- Electrical and magnetic fields
- Fluid flow rates
- Force, load, torque, and strain
- Humidity and moisture
- Leaks and fluid levels
- Velocity and displacement
- Temperature and pressure
Each of these may have several methods of measurement. For temperature, pressure, and others, a sensing element experiences a change in electrical resistance in proportion to the change in the phenomenon, which produces a change in signal voltage (often 0 to 5 volts, but PCB-mounted sensors are likely to have mV outputs) that is calibrated to the changes in the measured phenomenon. One position sensor locates the position of a magnetic field along a sensing tube. There are many other methods.
A transducer, a type of sensor, is a device that converts one form of energy into another. Common units in medical apps include sensors to measure temperature, pressure, forces, liquid levels, and flow rates. These physical quantities are converted to electrical signals in either analog or digital form. In motion control applications, transducers can refer to any one of a number of sensors, such as rotary or linear encoders, or resolvers for position feedback, such as tachometer for speed sensing, and even proximity switches to initiate or halt mechanical action.
If there is a trend in medical sensors, it is toward small and light-weight designs, and those that can sense small changes, and then function on millivolts.
The need for sensors will increase as more healthcare devices are connected to the Internet and wearable technologies become more prevalent.
