WEBVTT NOTE This file was exported by MacCaption version 7.0.06 to comply with the WebVTT specification dated March 27, 2017. 00:00:01.034 --> 00:00:04.972 align:center line:-1 position:50% size:62% Let us now discuss the intrinsic characteristics 00:00:04.972 --> 00:00:10.978 align:center line:-1 position:50% size:64% or key measurement parameters that are common across many types of sensors. 00:00:10.978 --> 00:00:14.381 align:center line:-1 position:50% size:45% Understanding them will help you choose the right sensors 00:00:14.381 --> 00:00:17.584 align:center line:-1 position:50% size:44% for your design and applications. 00:00:17.584 --> 00:00:21.722 align:center line:-1 position:50% size:38% Choosing the right sensor with the right characteristics 00:00:21.722 --> 00:00:25.826 align:center line:-1 position:50% size:42% may help improve the accuracy of your measurements, 00:00:25.826 --> 00:00:31.732 align:center line:-1 position:50% size:59% help you optimize your measurement speed without sacrificing accuracy, 00:00:31.732 --> 00:00:36.436 align:center line:-1 position:50% size:63% avoid the weakest range of a particular sensor, 00:00:36.436 --> 00:00:42.476 align:center line:-1 position:50% size:55% and even create an algorithm to extend your measurement capabilities. 00:00:45.479 --> 00:00:50.784 align:center line:-1 position:50% size:35% The sensitivity of a sensor is the ratio of change 00:00:50.784 --> 00:00:54.321 align:center line:-1 position:50% size:61% of the physical parameter input measurement 00:00:54.321 --> 00:01:00.460 align:center line:-1 position:50% size:47% versus the change of electrical output voltage or current. 00:01:00.460 --> 00:01:04.865 align:center line:-1 position:50% size:63% The figure shows the sensitivity of two sensors. 00:01:04.865 --> 00:01:08.502 align:center line:-1 position:50% size:48% Not all sensors have a linear output. 00:01:08.502 --> 00:01:13.307 align:center line:-1 position:50% size:45% Let us assume these two sensors have linear output. 00:01:13.307 --> 00:01:17.611 align:center line:-1 position:50% size:37% The sensor with the red line has higher sensitivity 00:01:17.611 --> 00:01:21.982 align:center line:-1 position:50% size:43% when compared with the sensor with the blue line. 00:01:21.982 --> 00:01:27.087 align:center line:-1 position:50% size:38% For example, if the sensor is an optical photodiode, 00:01:27.087 --> 00:01:32.826 align:center line:-1 position:50% size:36% its sensitivity is the change of lumens, light intensity, 00:01:32.826 --> 00:01:37.464 align:center line:-1 position:50% size:63% measured versus the change of output voltage. 00:01:37.464 --> 00:01:39.633 align:center line:-1 position:50% size:40% If the sensor is a thermocouple, 00:01:39.633 --> 00:01:43.036 align:center line:-1 position:50% size:37% the sensitivity is the change of temperature measured 00:01:43.036 --> 00:01:47.240 align:center line:-1 position:50% size:49% versus the change of output voltage. 00:01:51.111 --> 00:01:57.484 align:center line:-1 position:50% size:56% Dynamic range is a term that describes the total range that a sensor can measure 00:01:57.484 --> 00:02:00.187 align:center line:-1 position:50% size:47% from the physical input parameters 00:02:00.187 --> 00:02:04.791 align:center line:-1 position:50% size:41% such as light intensity, acoustic level, or temperature, 00:02:04.791 --> 00:02:08.762 align:center line:-1 position:50% size:47% and converts them into readable electrical parameters. 00:02:08.762 --> 00:02:13.166 align:center line:-1 position:50% size:44% It is the ratio between the largest and the smallest signals 00:02:13.166 --> 00:02:19.306 align:center line:-1 position:50% size:46% that are measurable by the sensor expressed in decibels, or dB. 00:02:19.306 --> 00:02:27.781 align:center line:-1 position:50% size:59% The figure on the left shows an example of a linear output of a sensor on the red line. 00:02:27.781 --> 00:02:31.685 align:center line:-1 position:50% size:46% The solid line defines the sensor's measurable range, 00:02:31.685 --> 00:02:35.589 align:center line:-1 position:50% size:54% and the dotted line is the possible output 00:02:35.589 --> 00:02:39.860 align:center line:-1 position:50% size:54% that is beyond the measurable capability of the sensor. 00:02:39.860 --> 00:02:45.332 align:center line:-1 position:50% size:51% The solid line determines the sensor's measurable dynamic range. 00:02:45.332 --> 00:02:50.237 align:center line:-1 position:50% size:52% Linearity is the difference between an actual curve sensor output 00:02:50.237 --> 00:02:55.008 align:center line:-1 position:50% size:37% versus an ideal straight line of a sensor output. 00:02:55.008 --> 00:03:02.215 align:center line:-1 position:50% size:49% Typically, sensors do not produce a typical straight line or linear output. 00:03:02.215 --> 00:03:07.387 align:center line:-1 position:50% size:49% They usually look curvy or may even have an abrupt drop off 00:03:07.387 --> 00:03:10.557 align:center line:-1 position:50% size:46% or change over its dynamic range. 00:03:10.557 --> 00:03:18.398 align:center line:-1 position:50% size:60% The blue line in the figure shows an example of a nonlinear sensor output. 00:03:18.398 --> 00:03:23.303 align:center line:-1 position:50% size:49% Its sensor output difference as compared to an ideal straight line 00:03:23.303 --> 00:03:30.710 align:center line:-1 position:50% size:56% or theoretical best straight line determines the extent of its linearity error. 00:03:33.413 --> 00:03:38.885 align:center line:-1 position:50% size:55% Sometimes all sensors have a hysteresis effect during measurements. 00:03:38.885 --> 00:03:44.991 align:center line:-1 position:50% size:47% For example, a temperature sensor can exhibit this hysteresis effect. 00:03:44.991 --> 00:03:50.097 align:center line:-1 position:50% size:53% If you measure a non-temperature point in the control oven 00:03:50.097 --> 00:03:52.833 align:center line:-1 position:50% size:41% from a cold to a hot temperature 00:03:52.833 --> 00:03:56.937 align:center line:-1 position:50% size:39% and then measure again from a hot to a cold temperature, 00:03:56.937 --> 00:04:01.041 align:center line:-1 position:50% size:48% the residual difference between the two temperature measurements 00:04:01.041 --> 00:04:05.779 align:center line:-1 position:50% size:37% represent the temperature hysteresis effect error. 00:04:05.779 --> 00:04:12.552 align:center line:-1 position:50% size:57% Similar hysteresis effects can also be noted with increasing and decreasing pressure 00:04:12.552 --> 00:04:15.822 align:center line:-1 position:50% size:54% when measured with a pressure sensor. 00:04:15.822 --> 00:04:24.598 align:center line:-1 position:50% size:53% The hysteresis effect makes it look and feel like the sensor is resisting or is lagging. 00:04:24.598 --> 00:04:30.303 align:center line:-1 position:50% size:58% This lag depends on the inherent properties of the sensor materials 00:04:30.303 --> 00:04:34.241 align:center line:-1 position:50% size:45% or design of the sensing element. 00:04:34.241 --> 00:04:40.147 align:center line:-1 position:50% size:61% Hysteresis contributes to the non-repeatability of the sensor measurement. 00:04:40.147 --> 00:04:45.385 align:center line:-1 position:50% size:60% There are other reasons for non-repeatability besides hysteresis. 00:04:45.385 --> 00:04:49.890 align:center line:-1 position:50% size:48% When measuring at the lowest point of the sensor's dynamic range, 00:04:49.890 --> 00:04:57.430 align:center line:-1 position:50% size:56% non-repeatability can occur due to the sensor's susceptibility to noise. 00:04:57.430 --> 00:05:03.537 align:center line:-1 position:50% size:51% Sometimes it is due to electromagnetic interference or EMI 00:05:03.537 --> 00:05:10.310 align:center line:-1 position:50% size:40% from a proximity to other parts of electronic components. 00:05:10.310 --> 00:05:17.918 align:center line:-1 position:50% size:61% One of the most critical sensor characteristics is the measurement response time. 00:05:17.918 --> 00:05:23.089 align:center line:-1 position:50% size:42% It is a measurement of how fast the sensor reacts to change. 00:05:23.089 --> 00:05:28.128 align:center line:-1 position:50% size:41% Sometimes, it is referred to as a time constant of a sensor 00:05:28.128 --> 00:05:31.731 align:center line:-1 position:50% size:51% when it is subjected to a step change. 00:05:31.731 --> 00:05:38.305 align:center line:-1 position:50% size:50% A product designer will not want to register a sensor reading too early, 00:05:38.305 --> 00:05:43.276 align:center line:-1 position:50% size:49% as the information will be inaccurate. 00:05:43.276 --> 00:05:49.449 align:center line:-1 position:50% size:55% Td, as noted over here, is the delay time, 00:05:49.449 --> 00:05:58.658 align:center line:-1 position:50% size:51% the time it takes to reach 50% of a steady-state value for the first time. 00:05:58.658 --> 00:06:06.533 align:center line:-1 position:50% size:49% Tp is the peak time, the time it takes to reach the maximum reading 00:06:06.533 --> 00:06:11.571 align:center line:-1 position:50% size:52% for the first time for a given excitement. 00:06:11.571 --> 00:06:18.278 align:center line:-1 position:50% size:60% Ts is the time it takes to reach a steady-state wave repo amplitude 00:06:18.278 --> 00:06:22.382 align:center line:-1 position:50% size:50% within the desired steady-state value. 00:06:22.382 --> 00:06:30.090 align:center line:-1 position:50% size:54% The steady-state error is a deviation of the actual desired steady-state value.