Sensor Specifications

Question 1

Static performance specifications

Answer 1

apply to steady-state measurement conditions

include: range, full scale, resolution, repeatability, accuracy, sensitivity, hysteresis, linearity, deadband

Question 2

Dynamic performance specifications

Answer 2

apply when the quantity being measured varies over time
include: response time, rise time, settling time, time constant, stability, bandwidth, lower frequency limit, upper frequency limit

Question 3

Range

Answer 3

the limits between which the quantity being measured can vary
units: quantity being measured

Question 4

Full scale

Answer 4

difference between the maximum and minimum values that the sensor can measure
units: quantity being measured

Question 5

Resolution

Answer 5

smallest change in the quantity being measured that is detectable by the sensor
units: quantity being measured

Question 6

Repeatability

Answer 6

the ability of a sensor to produce the same output for repeated applications of the same input (±3σ)
units: quantity being measured or % of full scale

measures the random errors of the sensor (due to electrical, thermal, and mechanical noise)

Question 7

Accuracy

Answer 7

the maximum extent the output of the sensor may be incorrect over its range (includes both random and deterministic errors)
units: quantity being measured or % of full scale

Question 8

Sensitivity

Answer 8

the ratio of the magnitude of the sensor output to the magnitude of the quantity being measured
units: (sensor output) / (quantity being measured)

Question 9

Cross-sensitivity

Answer 9

with directional sensors, the sensitivity of the sensor output to inputs orthogonal to the measurement direction

Question 10

Deadband

Answer 10

the band of input values for which there is zero input

units: quantity being measured

Question 11

Linearity

Answer 11

the maximum error between the mean values of the sensor’s outputs and the true values of the quantity being measured (related to accuracy but does not include the random component of error)
units: quantity being measured or % of full scale

Question 12

Hysteresis

Answer 12

the maximum difference between the calibrated sensor outputs for continuously increasing and continuously decreasing inputs
units: quantity being measured or % of full scale

Question 13

Response time

Answer 13

the time the output takes to reach 95% of the input when the input is a step
units: seconds or milliseconds

Question 14

Rise time

Answer 14

the time required for the output to increase from 10% to 90% of its steady-state value for a step input
units: seconds or milliseconds

Question 15

Settling time

Answer 15

the time required for the output to settle with +/- 1% of its steady-state value for a step input
units: seconds or milliseconds

Question 16

Time constant

Answer 16

the time required for the output to reach 63.2% of its steady-state value for a step input (assumes the sensor has a first order transfer function)
units: seconds or milliseconds

Question 17

Stability

Answer 17

the ability of a sensor to produce the same output when measuring a constant input over an extended period of time (a change in the output under these conditions is called drift)
units: (quantity being measured or % of full scale) / (time unit)

Question 18

Bandwidth

Answer 18

the lowest frequency at which the magnitude of the sensor transfer function drops by 3 dB
units: Hz

Question 19

Lower frequency limit

Answer 19

the lowest frequency at which the magnitude of the sensor transfer function equals -L dB
units: Hz

Question 20

Upper frequency limit

Answer 20

the lowest frequency at which the magnitude of the sensor transfer function equals +L dB
units: Hz

Question 21

Sensor calibration

Answer 21

1. apply a constant input at the start of the range of the sensor
2. measure the sensor output multiple times (at least 100)
3. calculate the mean value and standard deviation of the measured outputs
4. increase the input and then hold it constant
5. repeat steps 2 and 3
   6 repeat steps 4 and 5 until the input is at the end of the range of the sensor
6. fit a calibration line to the mean values of the measured outputs
7. implement the calibration
8. calculate static specifications

Question 22

What specification magnitudes do we want for an ideal sensor?
range, resolution, repeatability, accuracy, sensitivity, cross-sensitivity, hysteresis, deadband, linearity, response time, rise time, settling time, time constant, bandwidth, stability

Answer 22

range - large
resolution - small
repeatability - small
accuracy - small
sensitivity - large
cross-sensitivity - small
hysteresis - small
deadband - small
linearity - small
response time - small
rise time - small
settling time - small
time constant - small
bandwidth - large
stability - small