User Tools

Site Tools



This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
theory:sensor_technology:std_schmitt_trigger [2018/10/16 06:17] ↷ Links adapted because of a move operation
— (current)
Line 1: Line 1:
-====== A Schmitt Trigger for sensor level detection ====== 
-//We have seen [[st4_sensor_theory#​Transfer curve and non-linearity|hysteresis in sensors]]: we can use hysteresis in the comparator to eliminate noise. A Schmitt trigger is a comparator circuit that incorporates positive feedback. As a result, the comparator decision level for a low-to-high transition is higher than the comparator decision level for a high-to-low transition.//​ 
-For a signal with some noise, a plain comparator circuit may result into some transition noise in the output signal which is similar to contact bounce. In <imgref ReadOut16>​ we can see the comparator output for a clean signal. What happens with a noisy signal can be seen in <imgref ReadOut17>​. 
-<​imgcaption ReadOut16|Output of a comparator when the input is clean>​{{.measurement_theory:​readout16.png?​300}}</​imgcaption>​ 
-<​imgcaption ReadOut17|Output of a comparator when the input is noisy>​{{.measurement_theory:​readout17.png?​300}}</​imgcaption>​ 
-This response is quite logical because on a mV scale the signal does cross the decision level  multiple times before it becomes "​high"​ in the end. Just like contact bounce, a solution is to use a low-pass filter or software way of transition detection. However, a more appropriate solution for this problem is to use a higher decision level for a low-to-high transition and a lower decision level for a high-to-low transition. The comparator that does this is called a Schmitt Trigger and has the symbol of <imgref ReadOut19>​. 
-<​imgcaption ReadOut19|Schmitt trigger symbol>​{{.measurement_theory:​readout19.png?​100}}</​imgcaption>​ 
-The circuit is the comparator of <imgref SchmittTrigger01>​ with a positive feedback loop. As a result, the comparator level on $V_{in+}$ is different for a high $V_{out}$ than for a low $V_{out}$. Based on these two positions, we can calculate the relation between the resistors and the two decision levels. ​ 
-<​imgcaption SchmittTrigger01|Comparator with positive feedback>​{{.measurement_theory:​schmitttrigger01.png?​200}}</​imgcaption>​ 
-In <imgref SchmittTrigger02>​ the effective position of the resistors is drawn for two situations: where the output is high and where the output is low. 
-<​imgcaption SchmittTrigger02|Effective resistor connection in comparator with positive feedback for two states>​{{.measurement_theory:​schmitttrigger02.png?​400}}</​imgcaption>​ 
-The final response and effect is drawn in <imgref SchmittTrigger03>​ and <imgref ReadOut20>​. 
-<​imgcaption SchmittTrigger03|Input-output relation for Schmitt trigger>​{{.measurement_theory:​schmitttrigger03.png?​300}}</​imgcaption>​ 
-<​imgcaption ReadOut20|Illustration of how a double decision level system (Schmitt trigger) results into a noise free response>​{{.measurement_theory:​readout20.png?​400}}</​imgcaption>​ 
-====== Sensor Technology TOC ====== 
-These are the chapters for the Sensor Technology course: 
-  * Chapter 1: [[theory:​sensor_technology:​st1_measurement_theory|Measurement Theory]] 
-  * Chapter 2: [[theory:​sensor_technology:​st2_measurement_errors|Measurement Errors]] 
-  * Chapter 3: [[theory:​sensor_technology:​st3_measurement_technology|Measurement Technology]] 
-  * Chapter 4: [[theory:​sensor_technology:​stb_conventions_for_good_graphs_and_tables|Circuits,​ Graphs, Tables, Pictures and Code]] 
-  * Chapter 5: [[theory:​sensor_technology:​st4_sensor_theory|Basic Sensor Theory]] 
-  * Chapter 6: [[theory:​sensor_technology:​st6_sensoractuatorsystems|Sensor-Actuator Systems]] ​ 
-  * Chapter 7: [[theory:​sensor_technology:​st7_modelling_main|Modelling]] 
-  * Chapter 8: [[theory:​sensor_technology:​st8_accelerometer_model|Modelling:​ The Accelerometer]] - example of a second order system 
-  * Chapter 9: [[theory:​sensor_technology:​st9_scaling|Modelling:​ Scaling]] - why small things appear to be stiffer 
-  * Chapter 10: [[theory:​sensor_technology:​st10_lumped_element_models|Modelling:​ Lumped Element Models]] 
-  * Chapter 11: [[theory:​sensor_technology:​st11_finite_element_models|Modelling:​ Finite Element Models]] 
-  * Chapter 12: [[theory:​sensor_technology:​st12_impedance_spectroscopy|Modelling:​ Transducer Characterization by Impedance Spectroscopy]] 
-  * Chapter 13: [[theory:​sensor_technology:​st13_lumped_element_models_advanced|Modelling:​ Systems Theory]] 
-  * Chapter 14: [[theory:​sensor_technology:​st14_differential_equation_numerical_models|Modelling:​ Numerical Integration]] 
-  * Chapter 15: [[theory:​sensor_technology:​st15_signal_conditioning_and_sensor_read-out|Signal Conditioning and Sensor Read-out]] 
-  * Chapter 16: [[theory:​sensor_technology:​st16_resistive_sensors|Resistive Sensors]] 
-  * Chapter 17: [[theory:​sensor_technology:​st17_capacitive_sensors|Capacitive Sensors]] 
-  * Chapter 18: [[theory:​sensor_technology:​st18_magnetic_sensors|Magnetic Sensors]] 
-  * Chapter 19: [[theory:​sensor_technology:​st19_optical_sensors|Optical Sensors]] 
-  * Chapter 20: [[theory:​sensor_technology:​st20_actuators|Actuators]] - an example of an electrodynamic motor 
-  * Chapter 21: [[theory:​sensor_technology:​st21_actuator_models|Actuator principles for small speakers]] 
-  * Chapter 22: [[theory:​sensor_technology:​st22_adc_and_dac|ADC and DAC]] 
-  * Chapter 23: [[theory:​sensor_technology:​st23_bus_interfaces|Bus Interfaces]] - SPI, I<​sup>​2</​sup>​C,​ IO-Link, Ethernet based 
-  * Appendix A: [[theory:​sensor_technology:​sta_easyunitconversion|Systematic unit conversion]] 
-  * Appendix B: [[theory:​sensor_technology:​stc_common_mode_rejection_ratio_cmrr|Common Mode Rejection Ratio (CMRR)]] 
-  * Appendix C: A Schmitt Trigger for sensor level detection 
theory/sensor_technology/std_schmitt_trigger.1539670621.txt.gz · Last modified: 2018/10/16 06:17 by