Jump to content

Frequency measurement function block giving a wrong reading

Recommended Posts

Hi all.
For a few years, I have been using the HSC frequency measurement on the V350. 
My program uses the example that was given by Unitronics and I have not altered it much. 

Suddenly, my programs have stopped working when I download them to a new PLC.  The HSC behaves unusual and gives me false readings. 

My program is to control micro water turbines and it uses HSC to measure the frequency of the generator. I am using a simple frequency converter that gives me pulses into my HSCO port. The pulses are 50Hz and I confirm using a digital meter that the input receives 50Hz.

In the hardware setting, I define my input in the HSI(RELOAD) tap that my counter target value is 50 and I enable Reload on startup (See Hardware setup in attachment).

Hardware setup.JPG

Now in the ladder program, I define the "Frequency Measurement based on HSC" function block as shown in the picture. 

Ladder setup.JPG


When I run the program on my V350 I receive signal to my input and the actual HSC value is incrementing. I can see the number goes 50 steps for about 1 second so it's counting right (50Hz gives 50 pulses).
But my frequency seems to be off from the function block. 
See this video: https://streamable.com/ovzps

I measure about 62.11Hz with the function block.

The status message for the Frequency block jumps between 0 and 16. Zero means normal behavior but there's no explanation on what 16 means in the manual. 

Now if I change the Permissible delta (C-in the function block) to RAW measurement and start it again, this happens: https://streamable.com/tbt24
The counter slows down (lags) and I measure about 10Hz, and that makes no sense. 

Should I not receive about 50.00Hz? out of the function block? 
I tried to change PLC, tested on SAMBA and I am experiencing the same thing.

What am I missing. The only thing that has changed (I think)  is that I updated the Visilogic software and the firmware on the PLC.

A test program is at the bottom if you want to see it for your self.

Thank you






Link to comment
Share on other sites

Hi @Ausman!

Yes, I have and no luck, but you are correct on the firmware.
I just go with the newest visi version (Old habits), and it wants to upgrade to newer firmware to let me download the program into the vision. 

I found a vision350 PLC with older firmware and another computer with older Visilogic version. I tried my program and it works! 

I then upgraded the firmware on the vision and now it behaves same as I mention above. 

Now the question is, can I roll back on OS? :)
And can I report this bug somewhere to Unitronics

This version was in the PLC and this is the newest: (4.4 to 4.5)




Link to comment
Share on other sites

  • MVP 2023

You can roll back the OS, but you obviously need the relevant file to work with.  I can't remember this exactly, but I think all the matching O/S to the current version are in the Visilogic_C/Data folder.  In theory you can also add into this at will, and the O/S will show up in the list.

To me the easiest thing would be to (perhaps) do a system partition copy as a backup in case of something going completely wrong, uninstall the new version, reinstall the one you used and go from there.

Contact support@unitronics.com .  They can probably also give you the O/S easily, but I'd go the version you used path as above.  And also learn about Version Swapper, by reading all the topic that is pinned.  It is the reason it exists.

cheers, Aus

Link to comment
Share on other sites

  • MVP 2023

One of my many oft-repeated sayings: I NEVER update the firmware on a system in the field that is working properly. Never. I keep every copy of VisiLogic I have ever used on my computer and switch between them with Version Swapper as needed. I place a small text block in an unobtrusive place on one of the HMI screens with the VisiLogic version used to create the software so I can easily see which version to use for any needed updates.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...