S7-1200 ctrl hsc problem

Hello all,

I have a strange problem with a high speed counter with a s7-1200. I have set up the hack input - it is a 2 channel a/b type which gives 500 pulses per revolution. I also put the ctrl_hsc, created the data blocks etc. For some reason if I read the return directly from the encoder without the ctrl_hsc enabled (put an N/O in front of it) the return reads correctly at 500 pulses per revolution, however if I do it with the ctrl_hsc enabled it only reads about 120 pulses per rpm? I can’t understand or figure out why this is. Is anyone able to offer any advice?

About 120, would that be 125 by any chance. In which case you are looking for a calculation that includes the quadrature function of the AB high speed input. 500 / 4 = 125. Does the program allow for the quadrature output and so divide the HSC output by four, if so you should set the HSC to 'A/B Counter fourfold'.


One other thing, when you read the value of the HSC use the P option to get the reading right now. So instead of reading ID1000 you use ID1000. From the manual 'Append the suffix "" to the I/O address if you want the program to immediately access I/O data directly from the physical point instead of using the process image.'

Just a quick update on this. I have replaced the ctrl_hsc with a ctrl_hsc_ext and this has solved the problem. It seems the ctrl_hsc is a “legacy instruction” so I think that may have been having issues with the v4.2 firmware. I ha e bench tested it at the workshop and it’s all working spot on now so going to site tomorrow to update on site plc and hoping all will be ok.