Jump to content

Why are there only 24 MF blocks?

Recommended Posts

I'm evaluating a V133 for my company to potentially replace the DL06's that we currently use. And I hit this brick wall just now.

The application my company uses PLCs for uses mostly all floating point values. We have a lot of Analog inputs measuring tank levels and pressures.

I've read about jumping through hoops to use 2 integers to store the float values, but that's just not going to happen, because it shouldn't have to happen.

Why are there 2048 integer blocks, but only 24 float blocks?

Link to comment
Share on other sites

The V350 has 64, so it must be product specific. You could do some float math as an integer with implied decimals. Since there is not a good float display primitive for the HMI, I find the implied decimal approach to be frequently useful. Also with the formula block, you may find you need fewer floats to store intermediate calculations.

Link to comment
Share on other sites

  • MVP 2023

You're going to have to re-write the logic anyway, so consider this:

If you absolutely positively need a lot of floating point registers, then Unitronics will not work for you. Automation Direct uses a Siemens-ish dynamic memory allocation with its V-memory, so you can have pretty much whatever you want until you run out of memory.

A problem with this is that you have to manually keep track of where all your variables are, and since a float takes four registers they don't fall on even boundaries. Then there's the possibility that you can overlap them with each other and with your regular integers. Careful planning will avoid this problem, but it's still kind of a pain in the butt.

I do not use floats for analog scaling because it's almost never necessary. If the scaling can't be done with regular integers, there are also 255 signed long integers available. Consider the resolution of a floating point number in a PLC - you get seven digits of precision and a two-digit mantissa. A signed integer has a maximum value of 32,767, and a signed long integer has a maximum value of 2,147,483,648. That's 9.2 digits of precision and there are no rounding errors.

I only go into float land if trigonometric functions are needed.

Unitronics has a built-in HMI, as you already know. Displaying data on this HMI is much easier and more controllable using integers with virtual decimal points. To the user, the data looks the same and it's much easier to keep track of in the program as all the integers are individually numbered.

Plus, the software is free and there is never an upgrade charge. As opposed to a $395 buy-in. Take a long look at the Unitronics instruction set; it is intuitive and there are a lot more instructions available to you than Automation Direct.

Keep in mind that this is my personal opinion and I do not work for Unitronics, but I have been a distributor for them for 10 years. I have been programming PLC's for 23 years and have programmed them all, as I also do system integration work. Unitronics simply offers the most bang for the buck.

Joe T.

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...