PLC programming algorithm: switch, analog, pulse volume - the three relations

In the PLC is three a lot: the switch quantity, analog, pulse volume. Only in the clear the relations between and among, you can skilled master PLC controller.

1, the switch quantity logic, also known as means only two values, 0 or 1, ON or OFF. It is the most commonly used control, it is the advantage of PLC control, is also the most basic application of PLC.

is the purpose of the clearance volume control, according to the input current of switch quantity combination and history of the input sequence, make the PLC produces the corresponding switch output, in order to make the system to work in a certain order. So, sometimes also called the sequential control.

and sequence control is divided into manual, semi-automatic or automatic. And use the control principles of dispersion, centralization and three kinds of hybrid control.

this is the switch quantity with omron written in a 'single start-stop button' program.

2, analog refers to some of the continuous changes of physical quantities, such as voltage, current, pressure, speed, flow, etc.

after the PLC is introduced by relay control micro processing technology, which can be easily and reliably for on-off control. Due to the analog quantity can be converted to digital quantity, digital quantity more than just the switch quantity, so after converting the analog quantity, will have reliable PLC for processing control.

analog are common due to the continuous production process, so the analog control sometimes called process control.

analog is power, and the PLC can only deal with digital quantity, power. All in order to realize the conversion between them must have the sensor, the analog conversion into electricity. If the battery is not standard, pass transmitter, non-standard power into a standard electrical signals, such as 4 - 20mA、1— 5V、0— 10 v, etc.

at the same time also has analog input unit ( A / D) To keep these standard electrical signals into digital signals; Analog output unit ( D/A) PLC after processing the digital quantity, in order to convert into analog - — Standard electrical signals.

conversion between standard electric signal, the digital quantity, so it is used all kinds of operation. This needs to clear up the resolution of the analog unit as well as standard electrical signals. For example: the resolution of the PLC controller simulation unit is 1/32767, the corresponding standard power is 0 - 10 v, to detect temperature value is 0 - 100℃。 The 0 - Corresponding to 0-32767 Temperature of 100 ℃. Then calculate the corresponding digital quantity will be 1 ℃ is 327. 67. If you want to put the temperature value to 0. 1 ℃, the 327. 67/10 is ok.

analog control include: feedback control, feedforward control, proportional control, fuzzy control, etc. These are the PLC controller internal digital quantity calculation process.

3, pulse volume is its values are always in 0 ( Low level) And 1 ( High level) Variations between digital quantity. The number of pulses per second change alternately called frequency.

quantity of PLC pulse control purpose is mainly position control, motion control and path control. For example: pulse number in the application of the Angle control. Stepper motor drives the segmentation is each lap 10000, required stepper motor rotate for 90 degrees. So the pulse to be action value = 10000 / ( 360/90)

= 2500
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