Hello Forum,

I would like your  assistance please if possible.

So my question to you all is the following:

How can i measure an incoming external signal to know its period?  The minimum period would be 0.9ms and the maximum period 2.1 ms.

The input signal voltage would be 5 volts.

The PLC i would like to use is an S7 1200.

Also what is the data block to be used?

Thank you

Evangelos

Because of the voltage, you want a 5V TTL digital input SIGNAL board that plugs into the s7-1200 PLC module.

Then you can enable the HSC in the hardware configuration for that signal board.

One of the options is what data you want from the HSC input.

I know off-the-top-of-my-head you can select counts and frequency.  I think it provides period, but if it only provides frequency, it's simple math to calculate the period from frequency.

You can run a time interrupt OB every 2ms to perform the calculation (if required) if you need it fast.

Once you have the period, you can store it to a circular buffer (DB array) for processing from a cyclic OB/FB/FC.

The buffer only needs to hold a few data points.  Let's say PLC scan time is ~10ms.  5 data points will usually be plenty.  Every so often, the plc scan time will bump up to say 17 ms (like when establishing online connections using TIA Portal).  Then the buffer needs to hold at least 9 data points.  If it were me and I had a 10ms scan time, I would set aside room for 15 data points and generate a warning if it ever got full and lost data.

vanemm

Hello Forum,

I would like your  assistance please if possible.

So my question to you all is the following:

How can i measure an incoming external signal to know its period?  The minimum period would be 0.9ms and the maximum period 2.1 ms.

The input signal voltage would be 5 volts.

The PLC i would like to use is an S7 1200.

Also what is the data block to be used?

Thank you

Evangelos

Hello.

Get hold of the System Manual of the S7-1200 from here:
https://support.industry.siemens.com/cs/ww/en/view/109772940

There is a chapter dedicated to the use of the high speed counter. There is enough information to help you with your application. You will use the CTRL_HSC_EXT instruction.

There is also application examples. Focus on the first case mentioned on..
https://support.industry.siemens.com/cs/ww/en/view/109742346

The science guy™ mentioned the use of a signal board.