The primary functions of a Programmable Logic Controller (PLC) are reading sensors, executing sequence control programs, and updating actuators. PLCs interact generally with target plants by a time driven approach. That is, PLC captures the state change of the target plants and drives the actuators by acyclic scan. The period of the cyclic scan is called generally by a scan time (T).

PLCs are composed commonly of execution subsystems (ESs) and I/O subsystems (I/OSs). While I/OSs are interconnected over a system area bus in small scale PLCs, they are interconnected over a LAN (Local Area Network) in large scale PLCs. To provide enough bandwidth and low latency for data communication, the ES contains of a PEU (Program Execution Unit) and DTU (Data Transmission Unit) powered by separate processors.

The PEU refers to data in the IODM (I/O Data Memory) that consists mirror images of the actual values of the actuators and the sensors. The DTUs keep data coherency between the IODM in the ES and actuators or sensors in the IOSs. The PEU executes the program and the DTUs transmit the data with the period, T. the execution order of the I/O instructions of the sequence control program is not the same as the transmission order of the corresponding I/O data because the I/O data is packetized by the location of the IOSs and the data type. The execution time of the task and the data transmission time of the task should be counted independently. The execution time of the task and the data transmission time of the task should be counted independently in computing the PLC processing delay of a task. The data transfer delay between the DTU in the ES and the DTU in the IOS must be bounded. Currently, field bus networks have become suitable solutions for this purpose.

Since the PLC synchronous operates to the periodic time tick but handles asynchronous event of a plant, a shorter T enables PLCs to accommodate higher speed plant dynamics. Although the allowable minimum T often has accounted for a performance measure of PLCs, R indicates the performance more accurately. Generally, the state of the plant may change by both internal events and external stimuli. Sensing the plant state,

The PLC computes the suitable command to send to the plant within D. it does not respond to the command immediately after the plant receives the controller command. There is a delay on the change of the plant state. We denote the largest plant delay by P, L is the minimum control idle time, which is the minimum latency of a PLC from the control update to the next input sensing.

PLC often form the feedback control loops with the plant; it checks how the previous actuation influences the plant and determines the next value of actuation. The proper feedback control can be accomplished provided that P

The PLC senses the plant state at the beginning. The PLC actuates the output to make the plant state increase by one degree according to the control rule within the time bound D. the plant state increases following the PLC actuation of P. The plant state comes to the desired state fast. However, the plant becomes marginally unstable due to L

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In building professional model portfolios, vivacity is a finishing touch, it is added after the face has already shaped the immediate impression of happiness. A clear conception of the basic personalities and intensities of smiles helps you to suggest, duplicate and alter any smile.

Eyes are the life of all smiles. They must say something … and they must see something. Proper eye focus makes a smile flow in the right direction. When the director specifies a focal height or distance, the model must imagine something at that spot. Eyes focused on the floor might see a kitten; at eye-level… a person; upward … a bird; or, in the distance … a sailboat.

Sometimes dreamy eyes are not looking at anything in particular. They are actually searching for vacant spaces in which to paint pictures the mind sees. Dreamy eyes usually avoid direct contact with people and cameras.

Mouth positions can be prescribed by the use of words. Mouth-forming words of emotional value such as, Kiss? or Hurrah I have proved, in actual test, to have more meaning than the old photographic standby Cheese. Even though smiles should appear easy, the model’s mind must be on the job every moment. A temporary lapse may result in a picture showing that her mind walked off the scene leaving a blank smile to face the camera!

Contrary to common belief, the final success of a smile does not have to be left to chance.

Three simple steps build the right smile, to the right degree, at the right time and will help create fabulous professional model portfolios:
1. Identify the type of smile wanted.
2. Intensify it to the degree desired.
3. Add for plus value … vivacity.

Each smile has its own individual peak of freshness. It is the job of the model to produce its vivacity and the responsibility of the photographer to catch it.

Because enthusiasm is so contagious it befits each of those working together to put themselves, as quickly as possible, into the atmosphere and mood of the picture.

Positive comment on the part of the director and an enthusiastic frame of mind on the part of the model set the stage for climactic expressions.

The model creates while thinking, ‘I know the shade of meaning … I’m reaching for it … I’m getting it!’ The director encourages, ‘Now you’re getting it … that … that’s … That’s it!’ The director’s mind should be timed with the expression expanding within the model. Thus he can anticipate the approaching degree of the developing smile. Before it is reached (split seconds before he actually sees what he wants) he can start to press the shutter, allowing for the mental and mechanical time-lag necessary to stop the smile where he wants it.

A model rises to the peak of expression upon command when she steps out of her personal self and into the mood. She clears her mind of all else and is completely dedicated to that moment.

A director senses emotion to even a greater degree than his subject … his very being exudes the atmosphere in which expression grows.

Follow these suggestions, and you will capture just the right smile from your model and produce wonderfully professional model portfolios.

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