Trigger Signals: Sharp and Unsharp

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Triggered is said of Events with the most strict kind of correlation which may be imagined: the causative. Their effects are other Events.  After the introduction given here, it is clear that in the industrial technological applications it is still adopted the meaning for Event given between 1907 and 1915. A one century old meaning, today considered a classic approximation, where to a 3-dimensional spatial hypersurface and an associated clock is associated an exchange of energy in its different forms (e.g., electromagnetic, gravitational).   Triggering events along the electronic inspection involves the sequence:

  1. gating the Event2 occurrence in a pre-defined (Encoder pulses count) window whose centre has known distance to a precedent Event1, measured by mean of encoder pulses; 
  2. triggering (a measurement) upon occurrence of the Event2;
  3. capturing and processing the electrical signaling (data), acquired by another channel of information associated to one or more sensors, that follows the Trigger Event2.  

In what framework do we have to consider the basic measurement process we name Triggering, classic or modern ?  It was established long ago that Events happen in a Quantum Field and that several results are associated to the multitude of configurations in which the measurement process is defined in the Hilbert space. There, all possible results of the measurement (Triggering) coexist.  In the special branch we are, on the opposite, a single eigenvalue is perceived.  

The discovery of Decoherence cleared why the multiple coexisting results of measurements, named superpositions or pure states,  being of extremely brief duration are impossible to perceive for Us. However detected when using special instrumental arrangements like, e.g. during simple experiments of Quantum Optics involving the same identical beam splitters today universally present into camera-equipped Empty and Full Bottle Electronic Inspectors. This modern point of view was born in 1957, tailored since the start on an ideal device whose components and functions are a photocopy of that subset of the Binary Classifiers named Electronic Inspectors or, Bottling Controls.  In the following, it'll be shown the fine detail of the Triggering sequence as today it is considered be happening.



Example: 

Bottle Presence Trigger in a PET Empty Bottle Inspector

“Hilbert space represents a system before the measurement" 





“Why do we only experience individual sharp superpositions, single bowling balls, rather than multitudes ?”.  

Because all others get damped out by Decoherence, before we have the time to observe them.

The following figures, from a PET Empty Bottle Inspector in a Blow Molder Machine show the operation of the most common kind of Triggers, the Bottle Presence Trigger present in nearly all Beverage Bottling Line Machinery here playing the role of apparatus. Hinted, by mean of three figures, the branching structure of a vast set of alternative histories here reduced to the only two branches where the measurement (Triggering):

  • happened (two results);
  • did not happened (one result).

under the assumption that Triggering is happening in a closed system (not interacting with the Environment, in the classic spirit of Linear Systems).  Each Event is marked by the specific configuration to which it is referred (“Event”) thus fully adherent to  to the modern configurational meaning of Measurement

  • presence or absence of actions at certain times (Events);
  • presence or absence of components;

which makes the Event a unique label for a single instant of time in an alternative history.   




Branch created   

Event:

When t = 14.07.2009  13:04 the neck of a bottle is present along the trajectory of the LASER beam of light.

Signal to Noise relation is spiked or, sharp                                   










Branch created   

Event:

When t = 14.07.2009  13:04 the neck of a bottle is not present along the trajectory of the LASER beam of light.

Signal to Noise relation is spiked or, sharp                                      







Branch created   

Event:

When t = 14.07.2009  13:04  the LASER beam is not present.  The neck of the bottle lies, from the point of view of the Electronic Inspector, in an undefined status: no information to discriminate if it is present or not.

Signal to Noise relation is not spiked or, unsharp: there is no Signal nor Noise








“triggering is a multiple phenomena, interesting a multiplicity of fungible instances of the same and unique particle





Then, the three results depicted by the photographs above are referred to the same instant of time t, whose duration δt has however to be:    

                                                       δt   >  10-43 s

To that instant of time are referred a multitude of additional results different than those three. Each result being an Event triggered with different properties.    Why, a multitude ?     The answer, explained with plenty of details elsewhere in this web site, is based on the modern understanding of what can be directly and easily witnessed making use of Mach-Zehnder interferometers, invented over one century ago. These are devices based on a couple of beam splitters like those extensively used in the camera-equipped Full and Empty Bottle Electronic Inspectors illuminated by LASER light.  Another today common ingredient of all Full and Empty Bottle Electronic Inspectors in the beverage bottling lines. 

  

LASER triggering cans outfeeding a Seamer at 2.5 m/s 




Thin LASER beam triggering relatively fast objects like empty cans. Empty cans have also to be inspected when speeding at 7 m/s.  When an object moves faster, for example 30 m/s, triggers are based over 10 million times more energetic wave packets, the gamma-rays  

The answer requires a few steps:

  1. each one particle is the name given to the spaces where sufficiently many such spread-out probability functions  Ψ1,…Ψ2,…Ψi,…ΨN  are superposed, building up a localized wave packet.  Wave packet effect of the constructive interference occurring where the phases of the several individual waves superpose themselves and agree;
  2. particles are fungible.  Fungibility is a term coined long time ago for econonomic purposes. Cash particularly, has the widest fungibility: a bank note can be interchanged with two bank notes whose value is one-half. Taxes can be paid with one-hundred bank notes or one banknote whose value is one hundred times greater.  Beer or soft-drinks bottles, cans, crates or cases are conditionally fungible. The condition being that the interchange is allowed for packages of the same type and value.  Particles, name attributed to constructive superpositions of waves, sport the widest thinkable fungibility;
  3. particles exist simultaneously in different places of the same space, each one being an instance of the same. The particle really is unique, as seen by an higher dimensional and multiversal point of view;
  4. the system:

                   trigger  +  container 


is the aggregation in a limited space of a multitude of particles.   It inherits the physical properties listed above for the particles.  T his, is a concept clear to whoever has truly understood the mathematical idea underlying a linear combination.   A concept typically met at the first year of a Bachelor of Science (B.Sc.) university courses.   Also, an idea strictly related to the physical and philosophical conception of causality, the set of theories about existence and relation between cause and effect.   Unfortunately, causality is one of those subjects nearly never developed in the courses of Engineering (and developed the most verbose and unconcluding way, by philosophers…).   The net sum is that triggering is a multiple phenomena, interesting a multiplicity of fungible instances of the same and unique particle.   This is the meaning of the counterintuitive figures before, showing three fungible instances of the same and unique triggering.   Given initial conditions, a measurement is made:

time = t1 

  1. Measurement;
  2. No measurement.

The branch “No measurement”  is that one where (lowest shot in the sequence of photos above) the system configuration allowing measurement was not fulfilled (in our case, no LASER light).   The branch where measurement happens branched itself in two cases, following the fact that the Trigger gave out a highlow or signal, respectively corresponding to: 

time = t2

  1. Container Presence;
  2. Container Absence.

The only case of Presence shown furtherly developed in the four of the many conceivable cases at:

time = t3 

  1. Container Presence;
  2. Floating;
  3. Container Absence;
  4. No measurement.  






 Triggering process in a closed Environment.  Given initial conditions, at time = ta measurement is made determining at successive time = t2 also a branching where no measurement happens (lowest shot in the sequence of above) because all of the underlying conditions are not met.  The branch where it happens branches in two cases, following the fact that the Trigger gave out a “high” or “low” signal, respectively corresponding to:  (1) Container Presence + (2) Container Absence. The only case of Presence shown, furtherly developed in the four total conceivable cases at time = t3 (1) Container Presence + (2) Floating + (3) Container Absence + (4) No measurement.  Analog considerations are valid for the branches above left blank









Similar considerations are valid for all branches here left blank. Following the branch corresponding to a measurement happened   implicitly we have no information about the multitude of alternative histories which followed "No measurement” precondition.   Tree-like structure complete information lies in the wave function for the superimposed system:

                                                trigger  +  container 


fully described in a subset of the state space, named Hilbert space. 


 3-D sharp (spiked) and unsharp distributions for the Probability of a status of an objects, derived by physical measurements of its properties X, Y.  Electronic Inspectors' physical measurements, with extremely rare exceptions, are based on electromagnetic interactions between a sensor and the object (e.g., a container)





The shape of its distribution we perceive in terms of a Probability for the different results of the Triggering operation.  The results suggested by these three cases shall be examined one-by-one in the table below in terms of their sharpness, answering an intuitive question: in what a way is it distributed the information about the status of the presence of the bottle ?

 

  ____________________________________________________________________________________________________________

  Event     Observed                    Information        Physical meaning


  1.          Trigger and bottle                 Sharp              Measurement possible and happened with a defined result

     2           Trigger and no bottle           Sharp               Measurement possible and happened with a defined result

     3.          There is no light beam         Unsharp           Measurement not possible. Resulting information unsharp:

                                                                                        a 2-D surface parallel to the plane X - Y

  ____________________________________________________________________________________________________________________

                 Distribution of the information about the presence of the bottle in a PET Empty Bottle Inspector





 


This way to synthesise the conditions of what we name Signals, is common thru all Electronics.    An  example  appears  in the following  diagram, showing a  power  spectrum analysis with the frequencies on the horizontal axe in the range of frequency (0 - 200) MHz.  On the vertical axe, signals’ intensities are scaled in decibel, and range from a minimum of -100.0 dBm  (0.1 pW,  in SI units) until a maximum of 0.00 dBm (1 mW, in SI units).  Displayed four prominent Signals between hundredths others.    Only those four whose frequencies are:  (0, 50, 100, 150) MHz, emerge by the background noise.   The  power  amplitude  of  the  signal  marked  in yellow colour 1, peaking at the coordinates (50 MHz, 0.00 dBm) is the reference to scale all of the others.  Background signals range:  (-75 dBm; - 85 dBm), around 10 pW only, say ~10-8  times less powerful than the Signal 1.


 Spectrum Analysers  show all signals existing in a range of frequencies.  Figure above evidence the sharp presence of the Signal 1, whose power is ~ 100 million of times greater than the many small amplitude signals in the background normally considered “noise”.  On the horizontal axe one division equals to 20 MHz.  Scanning the spectrum at intervals of 20 MHz, shapes “ sharp" and “unsharp" like those described in the graphics of the figure above, shall distinctly appear.  Mainly areas whose amplitude is ~ -80 dBm but also four areas corresponding to frequencies (0, 50, 100, 150) MHz, whose amplitudes peak at  (-10, 0, 56.83, 69) dBm  





The Edge Trigger

        

            

  7417 is TTL hex buffers/drivers feature high-voltage open-collector outputs, here seen in two different kinds of packages.  Commonly devoted to interfacing with CMOS high-level circuits or for driving high-current loads (lamps or relays), and also used as buffers for driving several TTL inputs. In the bottom, shown its version 5417  qualified for the critical military applications

At the heart of every basic, advanced, and software trigger is the Edge Trigger, the most important of all triggers.  It’s conceptually the easiest trigger to understand and, in brief, to be Edge Triggered means we'll be notified about the Event occurrence only when the Event is detected.   We’ll choose the Edge-triggered systems, if we:

  • need a notification about the availability of the data to be read, we'll only get it when data was not available to read before, but now it is;
  • read some of the available data, in such a way that if the remaining data is still available to be read, we’d not get another notification;                                                
  • read all of the available data, then we’d get another notification when data became again available for reading.                    

The Edge Trigger comes in three forms: 

  • rising, 
  • falling;
  • rising and falling.  

It resides at core of the triggering system, providing a window into the workings of a triggering system.    The Edge Trigger is the key component of the entire system.   In the following images, to easy their comprehension, we’ll show examples referred to sinusoidal waves.  The same considerations are valid also for the squares and rectangulars waveforms that we’ll examine later, forms more commonly used in the Electronic Inspectors.    When observing the basic hardware functionality of an Edge Trigger, it can be categorized as a simple comparator that looks to see if the input signal crosses the entire threshold level, like in the figures down.   Edge Triggered Event means that the Event is triggered when the voltage (or, current, or temperature, or any other parameter) is spotted rising, which might be at the time marked (1), a time also named threshold level.   A preamplifier then processes the data, and the signal is digitized to a low level (logic “0" ) or an high level (logic “1”) following the polarity NPN or PNP of the semiconductor junction used.  0 and 1 are better considered ‘statuses', rather than indicators of potential, energy, etc.    Then, a trigger has sense only after some decisions, one hardware-related the other a mere choice, have been priorly made about what:

  • polarity, NPN or PNP, for the semiconductors junctions used
  • arming sequence, Falling Edge or Rising Edge or (Falling Edge + Rising Edge)



FallingEdgeTrigger

    Rising Edge Trigger 



RisingEdgeTrigger

   Falling Edge Trigger 


 

anyedgetrigger med hr

    Any Edge Trigger


Edge-Trigger Limitations

        

            Main types of Trigger              







  

Edge Trigger bandwidth is another relevant detail of this process.  The Edge Trigger chip’s comparators will only work until reaching a certain frequency.  If the frequency of the signal exceeds the Edge Trigger bandwidth, the Edge Trigger will not Trigger at all, even though the signal passed both thresholds.  That’s due to the timing between the comparator: if the signal passes too fast, the Edge Trigger will know that a signal crossed one threshold, but will not be fast enough to know if the second one was crossed.   This is one of the problems visibly affecting, in the crude practice, all of the Bottling Controls not operating standalone, rather with synchronisation sensors or inspections in-the-Machine.  Machine being a Filler, or Closer or Labeller.  Here, no one way exists to increase the sensitivity of the digital Inputs where these signals are wired for later processing in nor for the most common critical cases of Triggering.

Typical cases where this kind of problem is felt are whenever exist synchronisation sensors or inspections in the fast:

  • Filler Machines of a Canning Line, today normally operated at                                              > 90000 cans-per-hour;
  • Seamer Machines of a Canning Line, today normally operated at                                              > 90000 cans-per-hour;
  • Labeller Machines equipped with inspections in-the-Machine  (label presence detection photoscanners and Container Presence)  and synchronisation sensors (Machine Cycle, Filler Synchronisation), today frequently faster > 50000 bottles-per-hour;

and also in those applications which, not so fast in terms of container-per-hour digits, result equally or more critical because of other factors.   Between these last cases are remarkable:

  • Label inspection in-the-Machine, dependant on several factors with minimum or no possibility to adapt 
    • label inclination; 
    • sensor inclination;
    • label radius of curvature, format dependant;
    • label radius of curvature, position dependant (e.g., neck, collar, body, back);
    • label colour;
    • label material; 
    • label print; 
    • duration of the useful phase when labels are oriented toward the photoscanner light beam; 
    • distance between label and photoscanner; 
    • etc.
  • Aseptic Filling and Closing, because of the gravity of the consequences for the Final Customer and for the Customer, in case of contamination for an instance due to a non fully closed bottle;
  • Bottle Burst inspection in-the-Filler Machine, where a set of synchronisation sensors (Filler Synchronisation, Machine Cycle) cooperate with two inspections (Bottle Burst and Container Presence) to determine the eventual presence of extremely dangerous glass splinters in bottles filled adiacent to an exploded one.

A solution to this problem is commonly met, on the opposite, in the commercially available oscilloscopes, where the Trigger Sensitivity can be adjusted to the special conditions in which measurements have to be performed.  Here the Trigger Sensitivity is specified to accelerate the Edge Trigger bandwidth. Trigger Sensitivity specifies how large the signal needs to be at certain frequencies in order for a chip to Trigger.  The larger the signal, the easier it is for the Edge Trigger to work and, hence, the faster the Trigger can function.  


Level Trigger

Level Triggered means we’ll be notified whenever the Event is present, implying it will be true along a certain period of time.  With a Level Triggered system, we’ll have a notification whenever data is available to read.    A Level Triggered Event means that:

  • when the voltage reaches a particular level, the Event is triggered. As an example, at the time marked (2) in the examples in the figures above;
  • there would be two more (rising) Level Triggered Events in the trace, though no more (rising) Edge Triggered Events.   

In the special case of the Electronic Inspectors, levels can only be two, High and Low themselves depending on the initial hardware choice about the polarity of the semiconductors used, NPN or PNP.  Knowingly, NPN is the polarity corresponding to the Normally Closed switches logic, the one assuring major security with respect to the eventual:

  • cut of the conductors carrying the Signal;
  • failure, implying a permanently open circuit, of the switches and connectors part of the Signal's circuit. 

Comparing Edge Triggers and Level Triggers, because of what detailed above, Edge Triggered Events tend to be more stable than Level Triggered Events.  




"If a voltage signal ranging between 0.8 V and 2 V were to be sent into the input of a TTL gate, there would be                 no certain response from the gate. Such a signal would be considered uncertain, and no logic gate manufacturer would guarantee how their gate circuit would interpret such a signal



TTL and CMOS

Technologies

What examined before becomes relevant when applied to the special case of the Food and Beverage Bottling Lines Machinery where the Triggers of the Electronic Inspectors operate.  Here, hundredths of motors simultaneously running and frequency converters, add an important contribution, widening the spectrum of frequencies of the signals travelling along the conductors where Trigger sensors, photo-sensors or inductive-sensors are connected to the Inspectors’ IO circuits.  Our Triggers live in a noisy Environment.    An example of this in the Figure on left side, representing the same Trigger signal as seen in two different places of a circuit processing.  Today, the IO gate circuitry of the Electronic Inspectors is still mainly based on TTL logic, but however moving toward the CMOS standard. 



TTL acceptable

voltage range

TTL gates operate on a nominal power supply voltage of:

      VCC  =   (5.00  ±  0.25) V


Ideal a TTL integrated circuits' "high" signal would be 5.00 volts exactly, and a TTL "low" signal 0.00 volts exactly. Real TTL circuits cannot output themselves such ideal voltages. They'll accept “High" and “Low" signals deviating from these ideal values. Acceptable input signal voltages range from:

  • (0.00  -  0.80 ) V for a Low logic state;
  • (2.00  -  5.25) V for a High logic state.


The voltage levels guaranteed by the manufacturers over a specified range of load conditions range from 0 V to 0.5 V for a Low logic state, and 2.7 V to 5 V for a High logic state.

If a voltage signal ranging between 0.8 V and 2.0 V were to be sent into the input of a TTL gate, there would be no certain response from the gate.      Such a signal would be considered uncertain, and no logic gate manufacturer would guarantee how their gate circuit would interpret such a signal.   



CMOS acceptable

voltage range

CMOS technology is replacing TTL. These devices require lower power consumption and run off a lower nominal power supply voltage of:

                 Vcc  =  3.3 V 


instead of 5.0 V.   The fabrication technology itself is different for 3.3 V devices, allowing a smaller footprint and lower overall system costs. In order to ensure compatibility, most of the voltage levels are almost all the same as 5 V devices.   A 3.3 V device can interface with a 5 V device without any additional components.  For example, a logic “High" from a 3.3 V device will be at least 2.4 V.  This will still be interpreted as a logic "High" to a 5 V system because it is above the VIH of 2 V.    

When interfacing from a 5 V to a 3.3 V device it results necessary to ensure that the 3.3 V device is 5 V tolerant, say that the maximum input voltage is equal or superior to 5 V.  On certain 3.3 V devices, any voltages above 3.6 V will cause permanent a damage to the chip, making mandatory at least a voltage divider (e.g., a 1KΩ and a 2KΩ) to reduce 5 V signals to 3.3 V levels.




TTL noise margin

The tolerable ranges for output signal levels are narrower than for input signal levels.  This way, it becomes possible to ensure that any TTL gate outputting a digital signal into the input of another TTL gate will transmit voltages acceptable to the receiving gate.   

The difference between the tolerable output and input ranges is called the noise margin of the gate.   For TTL gates, the Low level noise margin is the difference between 0.8 V and 0.5 V (0.3 V), while the High-level noise margin is the difference between 2.7 V and 2.0 V (0.7 V).   

In other words,  the noise margin is the peak amount of spurious voltage that may be superimposed on a weak gate output voltage signal before the receiving gate might interpret it wrongly.   The margins for acceptable High and Low signals may be greater than what is shown in the previous illustrations. What is shown represents worst-case input signal performance, based on manufacturer's specifications. 




Threshold voltage

In practice, it may be found that a gate circuit will tolerate “High" signals of considerably less voltage and “Low" signals of considerably greater voltage than those specified here.   Conversely, the extremely small output margins shown, guaranteeing output states for “High" and “Low" signals to within 0.05 volts of the power supply variations are optimistic.  It is the amount of loading to really define if these output voltage levels will be true or not.   If the gate is sourcing or sinking substantial current to a load, the output voltage will not be able to maintain these optimum levels.  

Within the "uncertain" range for any gate input, there will be some point of demarcation dividing the gate's actual “Low" input signal range from its actual “High" input signal range. That is, somewhere between the lowest “High" signal voltage level and the highest “Low" signal voltage level guaranteed by the gate manufacturer, there is a threshold voltage at which the gate will actually switch its interpretation of a signal from “Low" or “High" or vice versa. 

For most gate circuits, this unspecified voltage is a single point. In the presence of AC noise voltage superimposed on the DC input signal, a single threshold point at which the gate alters its interpretation of logic level will result in an erratic output.




Schmitt triggers

To solve the problem presented by noisy inputs they can be applied Schmitt trigger gates to each one digital input of the Bottling Control.  Schmitt trigger can be considered a comparator with hysteresis (see figure on left side).  Their main feature is to ignores high frequency noise in their threshold voltage.  Noise below the threshold is ignored (see figure on left side, below) and positive feedback latches the output state until the opposite threshold is exceeded. 

The output is slew-rate limited by the operational amplifier response.  Considering how noisy the Food and Beverage Bottling packaging Line Environment is, this solution should have to be used as a minimum requirement before to buy an Electronic Inspector.   Schmitt triggers are distinguished in the schematic diagrams by the small hysteresis symbol drawn within them (see figure on left side, above). 

An hysteresis due to the positive feedback within the gate circuitry, adding an additional level of noise immunity to the prerformance of the gate. Also remarkable the fact that TTL inputs automatically assume a “High" state when left floating. 




















   Distortion self-evident when comparing the waveform in two different nodes of a circuit processing trigger signals





                

            TTL gates operate on a nominal power supply voltage (5.00  ±  0.25) V 






               

                     TTL acceptable input signal voltages range from:

                                                      (0.00  -  0.80 ) V for a Low logic state;

                                                      (2.00  -  5.25) V for a High logic state




                                                       


CMOS technology acceptable voltage range (logic families 3.3 V) 

  • VCC minimum output voltage level the CMOS device will provide for a High signal;
  • VOL maximum output voltage level the CMOS device will provide for a Low signal;
  • VIL  maximum input voltage level to still be considered a “Low” signal by the CMOS device;
  • VIH  minimum input voltage level to be considered a “High” by the CMOS device





              

  Threshold voltage is that one at which the gate will actually switch its    interpretation of a signal from Low or High or vice versa





                

  A slowly-changing DC signal with an AC noise superimposed is the most frequent operative condition for the logic circuits part of Food and Beverage Bottling Controls, making measurements and taking rejection decisions which may have (lethal) consequences for the Final Customers.  The figure shows that the Threshold itself could not prevent a double signal being Triggered when, in the reality, a single change happened from High to Low potentials.  We are here spectators of how easy it results to create False Triggers in a Bottling Control.  Traditional gate circuits, processing Trigger signals in the Electronic Inspectors, are better replaced by other Triggers, named Schmitt Triggers.  A special case where only a precedent second Trigger can substantially reduce the amount of the “False Trigger" signals outcoming from the first Trigger, devoted to containers




                

  The real signals infeeding TTL and CMOS logic gates in the Food and Beverage Bottling Lines and, in general, in the industrial applications, resemble the green colour, roughly approximating the square wave signal for which TTL and CMOS are designed.  Consider a Generator applying the signal Vin  to the inverting input of an amplifier (green colour).  Then, the out feeding (red colour) Vout  signal shall be an oscillating one.  In the example above, six square wave signals derive erroneously by two input signals



                                                       


The hysteresis symbol identifying the triggers of Schmitt





                                      

Schmitt triggers are comparators with hysteresis. Their main feature is to ignore high frequency noise in their threshold voltage.  The amount of positive feedback defined by the Ratio of the resistances (shown above as Rx 1 and Rx 10) latches the output until the opposite threshold is exceeded                      







  The rectangular signal is visibly affected by overwhelming Noise.     But, in Schmitt's Triggers tecnology the amount of positive feedback, defined by the ratio of the resistances (shown in the diagram above as Rx 1 and Rx 10), allows to latch the output until the opposite threshold is exceeded, thus resulting in a correct identification of the Signal buried in the Noise



High frequency Electronics is a privileged Engineering way to understand the unconventional meaning of words like measurement, signal or noise (image credit Agilent Technologies®)  TTL and CMOS

Technologies

What examined before becomes relevant when applied to the special case of the Food and Beverage Bottling Lines Machinery where the Triggers of the Electronic Inspectors operate.  Here, hundredths of motors simultaneously running and frequency converters, add an important contribution, widening the spectrum of frequencies of the signals travelling along the conductors where Trigger sensors, photo-sensors or inductive-sensors are connected to the Inspectors’ IO circuits.  Our Triggers live in a noisy Environment.    

An example of this in the Figure on left side, representing the same Trigger signal as seen in two different places of a circuit processing.  Today, the IO gate circuitry of the Electronic Inspectors is still mainly based on TTL logic, but however moving toward the CMOS standard. 





TTL acceptable

voltage range

TTL gates operate on a nominal power supply voltage of:

      VCC  =   (5.00  ±  0.25) V



Ideal a TTL integrated circuits' "high" signal would be 5.00 volts exactly, and a TTL "low" signal 0.00 volts exactly. Real TTL circuits cannot output themselves such ideal voltages. They'll accept “High" and “Low" signals deviating from these ideal values. Acceptable input signal voltages range from:

(0.00  -  0.80 ) V for a Low logic state;
(2.00  -  5.25) V for a High logic state.


The voltage levels guaranteed by the manufacturers over a specified range of load conditions range from 0 V to 0.5 V for a Low logic state, and 2.7 V to 5 V for a High logic state.

If a voltage signal ranging between 0.8 V and 2.0 V were to be sent into the input of a TTL gate, there would be no certain response from the gate.      Such a signal would be considered uncertain, and no logic gate manufacturer would guarantee how their gate circuit would interpret such a signal.   





CMOS acceptable

voltage range

CMOS technology is replacing TTL. These devices require lower power consumption and run off a lower nominal power supply voltage of:

                 Vcc  =  3.3 V 



instead of 5.0 V.   The fabrication technology itself is different for 3.3 V devices, allowing a smaller footprint and lower overall system costs. In order to ensure compatibility, most of the voltage levels are almost all the same as 5 V devices.   A 3.3 V device can interface with a 5 V device without any additional components.  For example, a logic “High" from a 3.3 V device will be at least 2.4 V.  This will still be interpreted as a logic "High" to a 5 V system because it is above the VIH of 2 V.    

When interfacing from a 5 V to a 3.3 V device it results necessary to ensure that the 3.3 V device is 5 V tolerant, say that the maximum input voltage is equal or superior to 5 V.  On certain 3.3 V devices, any voltages above 3.6 V will cause permanent a damage to the chip, making mandatory at least a voltage divider (e.g., a 1KΩ and a 2KΩ) to reduce 5 V signals to 3.3 V levels.





TTL noise margin

The tolerable ranges for output signal levels are narrower than for input signal levels.  This way, it becomes possible to ensure that any TTL gate outputting a digital signal into the input of another TTL gate will transmit voltages acceptable to the receiving gate.   

The difference between the tolerable output and input ranges is called the noise margin of the gate.   For TTL gates, the Low level noise margin is the difference between 0.8 V and 0.5 V (0.3 V), while the High-level noise margin is the difference between 2.7 V and 2.0 V (0.7 V).   

In other words,  the noise margin is the peak amount of spurious voltage that may be superimposed on a weak gate output voltage signal before the receiving gate might interpret it wrongly.   The margins for acceptable High and Low signals may be greater than what is shown in the previous illustrations. What is shown represents worst-case input signal performance, based on manufacturer's specifications. 





Threshold voltage

In practice, it may be found that a gate circuit will tolerate “High" signals of considerably less voltage and “Low" signals of considerably greater voltage than those specified here.   Conversely, the extremely small output margins shown, guaranteeing output states for “High" and “Low" signals to within 0.05 volts of the power supply variations are optimistic.  It is the amount of loading to really define if these output voltage levels will be true or not.   If the gate is sourcing or sinking substantial current to a load, the output voltage will not be able to maintain these optimum levels.  

Within the "uncertain" range for any gate input, there will be some point of demarcation dividing the gate's actual “Low" input signal range from its actual “High" input signal range. That is, somewhere between the lowest “High" signal voltage level and the highest “Low" signal voltage level guaranteed by the gate manufacturer, there is a threshold voltage at which the gate will actually switch its interpretation of a signal from “Low" or “High" or vice versa. 

For most gate circuits, this unspecified voltage is a single point. In the presence of AC noise voltage superimposed on the DC input signal, a single threshold point at which the gate alters its interpretation of logic level will result in an erratic output.





Schmitt triggers

To solve the problem presented by noisy inputs they can be applied Schmitt trigger gates to each one digital input of the Bottling Control.  Schmitt trigger can be considered a comparator with hysteresis (see figure on left side).  Their main feature is to ignores high frequency noise in their threshold voltage.  Noise below the threshold is ignored (see figure on left side, below) and positive feedback latches the output state until the opposite threshold is exceeded. 

The output is slew-rate limited by the operational amplifier response.  Considering how noisy the Food and Beverage Bottling packaging Line Environment is, this solution should have to be used as a minimum requirement before to buy an Electronic Inspector.   Schmitt triggers are distinguished in schematic diagrams by the small hysteresis symbol drawn within them (see figure on left side, above). 

An hysteresis due to the positive feedback within the gate circuitry, adding an additional level of noise immunity to the prerformance of the gate. Also remarkable the fact that TTL inputs automatically assume a “High" state when left floating.

  High frequency Electronics is a privileged Engineering way to understand the unconventional meaning of words like measurement, signal or noise (image credit Agilent Technologies®)


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