High Speed inputs in PLC
PLC has a characteristic of counter embedded in its software program library. A counter is not anything however a characteristic that counts things. For example, if we assign a sensor to a virtual enter of PLC.
The counter is configured withinside the PLC to paintings as a step-up counter. That approach, on every occasion the sensor adjustments a fee, the counter will increment it’s fee.
The counter is then programmed to be counted number best positive-aspect alternate (on every occasion the sensor is going from low to excessive, the counter will increment).
So, discuss with the under image, the counter increments on every occasion the sensor at enter adjustments from zero to 1 (low to excessive). Thus, we get the variety of instances the sensor has been sensed through the PLC.
High-Speed Inputs in PLC
But there are programs in PLC in which enter will alternate its fee so speedy that a ordinary counter of the kind mentioned will now no longer be capable of locate the alternate. This takes place due to the experiment time of PLC execution.
A counter is written in a ordinary segment of the PLC application and the segment has a regular experiment time of 5-10 milliseconds.
So, assume if an enter adjustments its nation often inside this time, then the counter will locate just a few adjustments and thus, provide a incorrect fee on the output.
Such styles of gadgets are encoders, excessive-velocity precision sensors, proximity sensors, laser sensors, etc.
High-Speed Counter (HSC)
For this purpose, we ought to use a excessive-velocity counter (HSC) in PLC. A High-Speed Counter is a characteristic this is used to be counted number such excessive-velocity inputs in a PLC.
So, assume we’ve got sixteen virtual inputs in a PLC CPU, 2-four inputs that may be configured as excessive-velocity inputs. That approach you may join such gadgets best to those inputs.
The wiring of a excessive velocity enter is classified into types – unmarried section and twin section. Single section approach a unmarried virtual enter can be used to increment or decrement the counter. Dual section approach virtual inputs can be utilized in aggregate to increment or decrement the counter.
Consider a proximity sensor for example of unmarried-section enter. Every alternate of nation (low to excessive) for that sensor at the virtual enter assigned will have an effect on the counter.
A twin-section enter may be taken into consideration as an encoder (You can use the encoder as a unmarried-section enter too).
An encoder has 3-section outputs from it. So, if one section output of the encoder (A) is used to be counted number withinside the ahead path and the alternative section output (B) is used to be counted number withinside the opposite path, the counter withinside the PLC will paintings in that way. This approach, if there’s an enter from A, then the counter will increment and if there’s an enter from B, then the counter will decrement.
Let us do not forget a few configuration parameters in a excessive velocity counter for greater distinctive information.
Selection of Input Type
As mentioned earlier, it’s far used to choose the form of wiring and configuration so that it will be carried out to paintings the counter accordingly.
Some of the maximum not unusual place modes used are – unmarried-section, A=Up and B=Down, A=Pulse and B=Direction, Normal Quadrature X1, Normal Quadrature X2, Normal Quadrature X4, Reverse Quadrature X1, Reverse Quadrature X2, Reverse Quadrature X4, etc.
The clear out time determines the most counting frequency so that it will be taken through the counter. Typical values variety from 0.002 ms to 4 ms (two hundred kHz to one hundred Hz).
The PLC indicates the corresponding most frequency for that. This approach, assume you choose 0.002 ms and the frequency corresponding is two hundred KHz.
The PLC will take a most of 200000 pulses in line with 2d from that virtual enter at a time. In quick, it’s going to take best one pulse in line with 0.002 ms interval.
So, indirectly, the frequency will increase as time decreases. This improves the efficiency, avoids noise withinside the machine and thus, reduces the impact of soar at the enter be counted number.
A virtual enter may be configured to synchronize or reset the counter fee. When the enter assigned is going excessive from low, the counter is reset.
As the counter is counting excessive-velocity pulses, there are times whilst even a mild motion of the tool will growth the counter fee to a outstanding extent.
Suppose, you’re the usage of an encoder. An encoder needs to be counted number the movement best whilst the machine is running, and now no longer whilst the machine is in forestall condition. If through chance, the encoder is moved through hand from someone, it’s going to convey undesirable counts in PLC.
To keep away from that, a virtual enter in PLC may be configured as permit enter. That means, the counter will take counts from the encoder handiest while there may be excessive ability at this enter or in easy terms, this enter is excessive.
Suppose you’re the usage of good judgment to provoke a device while the encoder has reached ten thousand counts.
Now, in case you use a everyday comparator withinside the application to evaluate set fee and encoder counts, the comparator will deliver an output after say 10500 counts. This takes place because of PLC experiment time.
A comparator is written in a everyday PLC section. So, to convey accuracy, there may be a provision to set the fee withinside the excessive-pace counter itself. When the counter reaches ten thousand, then it’s going to straight away deliver an output.
As mentioned earlier, primarily based totally on a threshold fee, the counter presents an output referred to as reflex output.
You can application it in normally 3 ways – set reflex output if the matter is much less than a threshold; set reflex output if the matter is among threshold values or set reflex output if the matter is extra than a threshold fee.
Due to those inner functions, you may reap more accuracy because the counter itself is doing all of the functions. The reflex output may be a smooth reminiscence bit or a bodily hardware virtual output from PLC.
This defines how the counter will feature in line with all of the parameters set. The maximum preferred ones used are – one-shot, modulo loop, loose large, event, frequency meter, etc.
All those parameters range from PLC to PLC and every one in every of it as it’s running style.
Thus, a excessive-pace enter is broadly utilized in gadget automation for accomplishing accuracy inside a targeted time; as mass manufacturing calls for excessive output in a brief span of time with most viable precision.