Sensors are electrical components that are used to measure other physical quantities (temperature, strain, flow, etc.) and produce electrical signals - usually voltage signals - that can be used to determine values for the physical quantity.

• Why learn about sensors?
• Electrical engineers need to know about sensors because they produce electrical signals.  Those signals need to be converted to digital format.  Those signals can be noisy and present a need for filter circuits, etc.  EEs are often called upon in the design and application of sensors.
• Mechanical, civil, chemical and bio engineers encounter sensors when they make measurements (temperature and other quantities).  They need to know about them in order to select appropriate sensors to make measurements of many different physical quantities.
• What do you need to know about sensors?
• You need to separate the variable being measured (which can be temperature, flow rate, pH, rotational rate, etc.) from the output of the sensor, which is usually a voltage, but could be a resistance, or the position of a dial on a meter.  Even though the physical output is usually a voltage, the frequency of the voltage might actually be the output.
• You need to know about different sensors.  There are many different physical effects that can be used to produce an electrical effect.  (Stretching a resistor changes the resistance in a strain gage, changing temperature causes a voltage in a thermocouple, etc.)  Those effects are used to build sensors.  You will want to become familiar with some typical sensors - particularly those sensors used in your particular discipline.
• Sensors do not respond immediately, and sensor dynamics is something you need to learn.
• What do you need to get out of this unit?
• When you are finished with this unit you should be able to do the following.
• Given a measurement requirement, be able to use the appropriate sensor to do the measurement, including measuring the sensor output and doing the appropriate conversions (electrical and calculation conversions).
• Determine some of the dynamic properties - time constants, particularly - of some typical sensors.
• What are you going to learn about?
• Temperature sensors
• Thermocouples
• Thermistors
• LM35 Integrated Circuit Sensors
• Strain Gages
• Flow Sensors
• Sensor time-constants.
• What if you need more information?
• There are links within lessons for individual sensors when we could find appropriate material.  Here are some interesting links.
• Practical Temperature Measurements - A classic reference on temperature measurement from Hewlett Packard.  It covers many different ways to measure temperature.
• A data sheet for the LM35.
• A data sheet for thermistors - with additional info on thermocouples.
• Problems
• Problem SensorDynamicsP01 - Predicting a Sensor Time Response
• Problem SensorDynamicsP02 - Calculating the Time Constant of a Sensor
• Problem SensorDynamicsP03 - Calculating the parameters of a Sensor

• Sensors - Material on kinds of sensors, time constants, etc.

        Here are some links to experiments you can do that will help you learn about sensors.

• An Introduction To Temperature Sensors
• Temperature Sensor Dynamics - Getting Data
• Temperature Sensor Dynamics - Calculating the Time Constants from Data
• A Thermistor Bridge