signalIt reflects the physical quantity of the message, and is the manifestation of the message. Information needs to be expressed and transmitted with the help of changes in some physical quantities (such as sound, light, electricity).The output signal is the result or information service provided by the system after input and processing. It is a concept in cybernetics. In cybernetics, the relationship between systems is divided into "input" and "output".When the output signal has control requirements, it can provide a switching signal to make the controlled equipment act.
The output signal is the result or information service provided by the system after input and processing. It is a concept in cybernetics. In cybernetics, the relationship between systems is divided into "input" and "output".When the output signal has control requirements, it can provide a switching signal to make the controlled equipment act.When the controller receives the input signal, according to the pre programmed program, the controller transmits the linkage control signal to the output module through the bus, and the output module starts the equipment to be linked;The equipment will receive a signal response after action.[1]
signal
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signalIt is the physical quantity reflecting the message, such as temperature, pressure, flow in industrial control, sound signal in nature, etc., so the signal is the manifestation of the message.What people say is information, which refers to the new content existing in the message. For example, when people get the original unknown information from various media, they get information.Visible information needs to be expressed and transmitted with the help of changes in some physical quantities (such as sound, light and electricity). The best example is that radio and television use electromagnetic waves to transmit sound and images.
The signals are divided into electrical signals and switching signals.Non electrical physical quantities can be easily converted into electrical signals through various sensors, and electrical signals are easy to transmit and control, so they become the most widely used signals.
Electrical signal refers to the voltage or current that changes with time, so it can be expressed as a function of time in mathematical description and its waveform can be drawn.Information is transmitted, exchanged, stored and extracted through electrical signals.The signals in the electronic circuit are electrical signals, which are generally referred to as signals.
Signal classification
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The forms of output signals are various and can be classified from different angles.Signal dependentRandomnessIt can be divided into deterministic signals andrandom signal；According to the periodicity of the signal, it can be divided intoPeriodic signalAnd aperiodic signals;According to the continuity of the signal, it can be divided intoContinuous time signalandDiscrete signal；Divide the signal intoanalog signalanddigital signal。
analog signal
Analog signal refers to the continuous signal of information parameters within a given range.Or in a continuous time interval, the characteristic quantity representing the information can be presented as a signal of any value at any instant, the amplitude of the signal, orfrequency, or the phase changes continuously with time, such as the current broadcast sound signal, or image signal.
digital signal
Digital signal refers torangeThe value of is discrete, and the amplitude representation is limited to a finite number of values.Binary code is a digital signal.Binary code is subject toNoiseIt is easy to be processed by digital circuits, so it has been widely used.
Linearization
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In the components of the detection device, there are often nonlinear links, especially the relationship between the output of the sensor and the measured physical quantity, most of which are nonlinear.There are two main reasons for nonlinearity: first, the conversion principle of many sensors is not nonlinear, such as temperature measurement, thermal resistance or thermocouple is nonlinear with temperature;For flow measurement, the relationship between the differential pressure signal output from the orifice plate and the flow input signal is also nonlinear;The second is the nonlinearity of the measuring circuit used. For example, a four arm bridge is used to measure thermal resistance. The change of resistance causes the bridge to lose balance, and the relationship between the output voltage and the resistance is nonlinear.[2]
The linearization processing of sensor output signal usually adopts one dimension table lookup method, linear interpolation method and calculation method.
One dimension table lookup method
When the conversion value is greater than the key item, the comparison process continues until the conversion value is just less than or equal to the key item.The comparison sequence value (i.e. the number of searches) is the temperature value obtained.For example, item 10 is the first key item less than or equal to the converted value,.If item 1 in the table is found, the above conditions can be met, and the measured temperature is the lower limit value.This method can adapt to different sensor characteristics.
The advantage of one-dimensional table lookup method is that it can adapt to different linearization requirements. If the characteristics of the sensor change, only the contents of the DEGTB table need to be changed, and neither the program nor the hardware need to be changed.The disadvantage of one-dimensional table lookup method is that when the measurement range increases or the parameter points become dense, because the length of the table increases, it will occupy a large number of storage cells and reduce the speed of table lookup.[2]
Linear interpolation
One dimensional table lookup has obvious disadvantages. When the measurement range increases or the temperature points become denser (higher conversion accuracy is required), the length of the table will increase sharply, which will inevitably occupy a large number of storage cells and reduce the speed of table lookup.Linear interpolationIt is an improvement on the one dimension table lookup method.
Linear interpolation method is equivalent toNonlinear functionThe accuracy of approximation depends on the number of polyline segments: the more segments, the higher the approximation accuracy.
Since the table used in the linear interpolation method is only the turning point of the passbook line, when ensuring the same linearization accuracy, the linear interpolation method saves a lot of storage cells compared with the one-dimensional table lookup method: although the calculation must be carried out according to the formula, because the calculation formula is simple, the calculation time is limited, and the accuracy is high.For example, if orifice plate is used to measure flow, the square root of differential pressure is linearized. When the broken line is divided into segments, the linearization accuracy can be better than 0.1%.[2]
Calculation method
When the characteristics of the sensor cannot be accurately described by mathematical equations, the above two methods are more appropriate.
For those nonlinear characteristics that can be described by mathematical equations, the measured parameters can be calculated directly by calculation method.
The calculation method is applicable to those nonlinear characteristics that can be described by mathematical equations.Because the calculation method requires multiple iterations to get the final result, the calculation method is slower than the linear interpolation method, and should not be used in situations with high real-time requirements.However, the advantage of the calculation method is that it does not need to create a table in memory in advance.[2]
