A sensor takes an input quantity and converts it to an output quantity. Sensors may be simple physical measurement systems, or complex electronic devices requiring sophisticated data acquisition systems. No matter the type of sensor, input type, or output type, every sensor has inherent characteristics that allow the user to select the right sensor for the task at hand.
Sensor Characteristics
Some sensor characteristics include:
- Input Range
- Output Range
- Accuracy
- Repeatability
- Resolution
Input Range
Input range is the maximum measureable range that the sensor can accurately measure. For example, a compression load cell may have an input range of 0 - 5000 pounds. The load cell cannot accurately measure "negative", or tensile loads, or compressive loads greater than 5000 pounds. Generally, quantities outside of the input range can be measured, but characteristics such as accuracy and repeatability may be compromised when the input is outside of the specified range.
Output Range
Output range generally refers to electronic sensors, and is the range of electrical output signal that the sensor returns. However, the output range could be a physical displacement, such as in a spring scale, or rotation, such as in a clock-style analog thermometer. The output range is related to the input range by the conversion algorithm specific to the sensor type, and the algorithm may include factors based on the calibration of the specific sensor.
Accuracy
Accuracy actually refers to the amount of error, or inaccuracy, that may be present in a sensor. Accuracy can be stated as a unit of measurement, such as +/- 5 pounds, or as a percentage, such as 95%. In most cases, increased accuracy results in an increased cost for a sensor.
Repeatability
Repeatability, as the name implies, refers to how often a sensor under the same input conditions will return the same value. If a sensor is designed to be used over and over again, it is important that the output value is accurate over every measurement cycle for the life of the sensor. Repeatability is determined by calibration testing of the sensor using known inputs.
Resolution
Resolution is the smallest unit of measurement that the sensor can accurately measure. Some transducers return output signals in discrete steps, and therefore the resolution is easily defined. Resolution can be stated as a unit of measurement or as a percentage. For electronic sensors, resolution is also dictated by the resolution of the signal conditioning hardware or software.
These qualities are common to all sensors, no matter what characteristic is being measured. All of these traits must be considered when selecting the right sensor for the specific needs of a test.
