Can i measure Speed via Digital I/P

As per i know we can measure speed via digital input, and i also did some projects with this.

But now i am using s7 1500 PLC where there is no CPU inbuilt IO's so with standard digital input what is the minimum frequency to calculate the speed.

Or is this any default DI is available for the high speed counter. 

Ok thanks,

I am using 1515-2 PN PLC.

So then i think i can use counter module for this PLC also. 

• TM Count 2x24V Counter Module
• TM PosInput 2 Position Input Module

To calculate the time between two digital signals:

• Time-based IO module TM Timer DIDQ 16x24V
  This example calculates the length, but the principle is the same.

OK

But my client dint want to use extra module for this,

So can i measure speed via standard Digital input. 

Hello,

I'll be strictly describe requirement use of specific module to have best results. Probably your Client don't understand that. If he want have good functionality, he also need depended HW. If he want save up money, not good idea.

It mainly depends on the pulse frequency you want to measure because you'll depend on the cycle time of the CPU and the actualisation time of your digital input card (and field network). As the counting is not done within board, it means that your CPU must have the time to read and count the rising edge of each pulse coming and then calculate a speed by taking the difference of pulses along a fixed time period.

Generally speaking it's a poor/cheap solution, but it can do the job for some not so accurate applications. For few Hz signal it can work, for kHz signal it will miss pulses.