AB Input DC SINK Module

Hello,can'i use AB DC-SINK module 1746-IB16 for hight speed cunter (encoder 250 pulse/tr) ,if is yes ,please send one exemple (RSLOGIX 500) or link ,if no please gives a reference of module how can doing this.
Thank's

Well, it would depend 50% on how fast you spin the encoder, and 50% on the resolution (250ppr)

In short, No, you can't use that card. The input refresh is (I'm recalling from memory, not a manual, so look it up if you need exact numbers) 8ms, plus your scan time - let's estimate 12 ms.
So the BEST you would get out of that car is 1cycle/20ms = 50 Hz. But, you also want to have at least a 2:1 ratio when using ladder scans to count, so you'd get - at best - about 25Hz.

You would need a HSCE or HSCE2 card to input that encoder. They go up to (again, from memory) 50kHz.

Can you Explain theses calculations in more detail?

I have never designed an encoder application

The input response time of the card would be in the milliseconds range.
The plc takes a finite time to scan the program this will depend on the number of instructions (each call to an instruction will take a time to process i.e. and = 4ns compare may take 2 ms so all the logic used will be a sum of all instructions (each contact, output or compare/math instruction with their given processing time + the update of the I/O.
in general most plc's will have a scan time of between 5 -100ms.
so if you need to count 25 pulses per second then the max scan time of the plc should be less than 10 ms to ensure every pulse is captured.
There are ways normal I/O cards can be used but it depends on the plc some will contain instructions to update immidiate I/O this instruction could then be used in a time interrupt.
Or if the plc will allow functions that can be called within the program then a function written to update I/O immidiate and call the block 10 times in the main routine (sprd between other routines then this can reduce the effective scan time.
i.e. if a program contained 10 sub programs & each one of these took 5ms this gives a total scan time of 50 ms not including the I/O & comms etc.
then calling the update I/O + process the count instructions ten times (one after each other routine) means that the effective update would be less than the 50ms total scan time.
I have used this on a number of S5 systems & it worked fine for what I call slow counts < 200 hz

A high speed counter will usually give the highest frrequency it can count. There are no calculations involved.

But ilhem and RoTaTech are discussing a pulse coming in via a standard input card and being counted by a standard counter within the PLC ladder. So we have two main considerations.\

1. What is the highes rate at which the input card can respond to changes OFF->ON and ON->OFF. Anything faster than these (less time in the ON state or in the OFF state) will basically not be seen. So that sets the first limitation.

2. Assuming the pulses are long enough to pass the input card we now have the scan time. This is the time from one input update to the next. A tech would have to look at the timing as read out from the current PLC program. In order to count at least one pass must happen with the input in the OFF state then at least one pass with the input in the ON state for one count to be made. It is necessary to have the ON and OFF times at least as long as the scan time. If it is ever less you risk loosing counts. A rule of thumb would be at least 1 1/2 the scan time for the ON and OFF time. (This is not the total time for a cycle, this the time for the shorter of either the ON or OFF time.)

Using these considerations you should be able to decide if a given encoder input can be used in this manner.

Makes more sense now. Thanks Bernie and Parky

You might want to consider adding a small Micrologix 1000
just for the HSC operation. It has an input filter you can
adjust for the speed. PNP I always herd has a much cleaner signal.

I need help to have programing example of encoder in Fatek PLC. I want to measure the length (or width)by encoder and based on this values have to drive motor upto this value. Please help me in this regard.
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