Unusual requirement, but sending messages to the PLC from your phone can be done, but just maybe in a different way. At least one way that I know of is to use the MQQT protocol via TF6701 TwinCAT 3 IoT Communication. From my understanding, there are MQQT phone apps that you can then use to send messages to the broker, which then get relayed to the PLC.

+1; get a better PLC.

Reliably detecting a filling event will likely be more difficult than calculating the dosing.

Calculations are easy; measurements are hard.

Logo manual here:
https://support.industry.siemens.com...?download=true
No it doesnt look like it can do floating point math.

Surprisingly it handles modem integration quite well and the Logo has a specific dedicated CMR2020 modem for it.
https://support.industry.siemens.com...?download=true


Up to +-5% is acceptable.

Yes this is exactly what is required. Thank you for summarising it perfectly!
What PLC would you recommend that would be capable?

Thanks Jesper. Totally Agree it makes sense to get capable Hardware rather than lost time looking for workarounds

Thanks for looking into this.
There is no LAN/WAN connectivity unfortunately.
These are 30 Remote sites which will all have this standalone PLC solution, so we need to be able to contact/interrogate the PLCs.

You need floating point, but you can do the calculation with multiplication and addition based on level.

Here you go.....

CU8210-D004-0103: LTE USB modem.

See pg. 8 of the documentation here. - "The USB stick can also receive and send text messages using the Short Message Service (SMS)"

Add the Cabinet dome for protection of the device.

Explore the various IPCs and Embedded PCs available. It appears your application is rather small and simple. Any IPC or CX equipped with USB port should work just fine. For applications where the PC/CX might be exposed to harsher environments, I would opt for something in the CX line (Embedded PC).

CORRECTION EDIT: The LTE stick can only operate with Windows 7, Windows 10, or TwinCAT BSD. This limitation may inherently omit a few of your options for PC/CX selection, as some of the "Economy" CX's are only available with Windows CE (ex..CX9020).

I would use a look up table. I would generate it using Mathcad but most would use Excel. Then do linear interpolation betweeun the points. If I needed more accuracy I would use Lagrange interpolation which is a 3rd order interpolation but I doubt this is required.

It is not; if accuracy to a percent or so is acceptable and square root is available (but no trig e.g. MicroLogix 1100), then linear is good enough (below from @Tom Jenkins's sheet; see here also).

Attachment 60648

atan(1) would be replaced by 0.785... in the actual case.

But on MicroLogix the lookup table would be available anyway.

Here you go....

FB_CTRL_LIN_INTERPOLATION

The caveat is that the above FB is part of a paid-for library (TF4100 Controller Toolbox), meaning if you want to use this for all 30 PLC's, you would need to purchase this library for each one of those 30 stand-alone PLC's. The cost of the library is dependent on the 'Performance Level' of the IPC/CX. We purchased the library for a performance level 70 IPC, and I believe the cost of it was ~$450 USD. For your application, a performance level 40 IPC/CX is all you would require, and that's only because you need the modem USB stick, which requires Win7 or Win10.

A much cheaper option in lieu of the TF4100 Controller Toolbox library:
Explore the FB's and Functions in the free OSCAT library I linked in a previous post, particularly "LINEAR_INT" on page 101, and "POLYNOMIAL_INT" on page 102. One of those should work for your application. The OSCAT library is free!!

You could also just code a polynomial in your logic. I did that for two of our machines in RSLogix500, with some pre-work in Excel.

Math is not the problem for any but the most rudimentary processor; this could be done even if only integer math was available, though it would be a mess.

So to answer the OP, look for something that handles the SMS requirement cleanly and has either floating point with square root, or the capability to store a lookup table.

A lot less time is going to be spent coding how much to dose than coding when to dose.

Thanks Tom

Thanks very much for your detailed response.
I am very impressed with Beckhoffs offerings and am in touch with the New Zealand agent now. Cheers!

Thank you very much for taking the time to look at this for me.
Cheers!