Calculation of switching quantities
1. switching quantity, analog quantity, pulse quantity switching quantity, also known as logic quantity, refers to only two values, 0 or 1, ON or OFF. it is the most commonly used control, the control of which is the advantage of the PLC, and is the most basic application of the PLC.
The purpose of switching control is to make the PLC produce the corresponding switching outputs according to the current input combination of the switches and the history of the input sequence, so that the system can work in a certain order. Therefore, it is sometimes referred to as sequential control.
And the sequence control is divided into manual, semi-automatic or automatic. And the control principles used are decentralized, centralized and mixed control.
2. Analog refers to some continuously changing physical quantities, such as voltage, current, pressure, speed, flow and so on.
PLC is developed by the introduction of microprocessor technology for relay control, which can be easily and reliably used for switching control. As analog can be converted to digital, digital is only a multi-bit switching, so the converted analog, PLC can also be completely reliable processing control.
Because continuous production processes often have analog, so analog control is sometimes called process control.
Analog is mostly non-electric, and PLC can only handle digital, electric. All to realize the conversion between them to have a sensor to convert analog into digital electricity. If the amount of electricity is not standard, but also through the transmitter, the non-standard amount of electricity into a standard electrical signal, such as 4-20mA, 1-5V, 0-10V and so on.
At the same time there should be analog input unit (A/D), these standard electrical signals into digital signals; analog output unit (D / A), in order to the PLC processing of digital quantities into analog - standard electrical signals.
So the standard electrical signals, digital conversion between the various operations to be used. This requires clarification of the resolution of the analog unit and the standard electrical signal.
Calculation of analog quantity
1. The resolution of the PLC analog unit is 1/32767, the corresponding standard power is 0-10V, and what is to be detected is the temperature value 0-100℃. Then 0-32767 corresponds to a temperature value of 0-100℃. Then calculate the digital quantity corresponding to 1℃ is 327.67. If you want to make the temperature value accurate to 0.1℃, put 327.67/10 can be.
2. Analog control includes: feedback control, feed-forward control, proportional control, fuzzy control, etc. These are all digital quantities within the PLC. These are the process of calculating digital quantities within the PLC.
3. Pulse is a digital quantity whose value is always changing between 0 (low level) and 1 (high level). The number of alternating pulse changes per second is called 3, for frequency.
PLC pulse quantity control purpose is mainly position control, motion control, trajectory control, etc.. For example, the number of pulses is used in angle control.
The subdivision of the stepper motor driver is 10000 per revolution, and the stepper motor is required to rotate 90 degrees. Then the pulse value to be acted = 10000/(360/90) = 2500.
1.-10-10V. A voltage of -10V-10V is converted to F448-0BB8Hex (-3000-3000) at 6000 resolution, and to E890-1770Hex (-6000-6000) at 12000 resolution.
2. 0-10V. 0-10V is converted to 0-1770Hex(0-6000) at 12000 resolution; and 0-2EE0Hex(0-12000) at 12000 resolution.
3. 0-20mA. 0-20mA current is converted to 0-1770Hex(0-6000) at 6000 resolution; 0-2EE0Hex(0-12000) at 12000 resolution.
4. 4-20mA. 4-20mA current is converted to 0-1770Hex(0-6000) at 6000 resolution and 0-2EE0Hex(0-12000) at 12000 resolution.
The above is only a brief introduction, different PLC has a different resolution, and the physical quantities you measure to achieve different ranges. Calculations may vary.
Note: Requirements for analog input wiring
1. Use shielded twisted-pair cables, but do not connect the shields
2. When an input is not in use, short the V IN and COM terminals.
3. Isolate analog signal lines from power lines (AC power lines, high voltage lines, etc.).
4. When there is interference on the power supply line, install a detector between the input section and the power supply unit.
5. After confirming the correct wiring, power up the CPU unit first and then the load.
6. Cut off the power supply to the load first, and then cut off the power supply to the CPU when the power is cut off.
Calculation of Pulse Amount
The control of pulse amount is mostly used for stepping motor, servo motor angle control, distance control, position . position control, etc. The following is an example of stepper motor to illustrate each control method.
1. Angle control of stepper motor. First of all, it is necessary to clarify the fine points of the stepper motor, and then determine the total number of pulses required for one revolution of the stepper motor.
Calculate "Angle percentage = set angle / 360 ° (i.e., a circle)" "Angle action pulse = a circle of the total number of pulses * angle percentage.
The formula is:Number of angle action pulses = - total number of pulses in a circle * (set angle/360°).
2. Stepper motor distance control. First define the total number of pulses required for one revolution of the stepper motor. Then determine the diameter of the stepper motor roller and calculate the circumference of the roller.
Calculate the distance to be run for each pulse. Finally calculate the number of pulses to be run for the set distance.
The formula is: set the distance of the number of pulses = set the distance / [(roller diameter * 3.14) / a circle of the total number of pulses]
3. The position control of the stepper motor is a combination of angle control and distance control.
The above is just a simple analysis of the stepper motor control, there may be discrepancies with the actual, only for the reference of colleagues.
The action of the same service motor is the same as that of the stepper motor, but we should consider the internal electronic gear ratio of the servo motor and the reduction ratio of the servo motor.