How this function works

 hello 

Thank you very much for your assistance and your always great help. 

I have a problem,  in a new project,  three temp transmitters( PIW 506, PIW 508 and PIW510) show 000 in the HMI. I connected my laptop to read the blocks. As you can see( please see the attachment file) they are identical as they are connected on three boilers.

Take, for example, PIW506 the #out3 of the FC4 read -118.519, which is stored in DB310 in DBD28.

however, when I opened the function to know how it was scaled and calculated  I found the #out3 read 30.38 which equlas to the measured temp 

Can anyone please help me how this works and how to get the #out3 read 30.38,  which then will be shown in the HMI

Please note the input channel is configured in 4wire and the transmitters is powered and local LCD show 30C

Thannk you very much in advance 

Thank you very much indeed for your response

I am attaching herewith this post the online statue of FC4 as you can see the  #out3 reads -118  (see page #1 in the attached file)

Also, I opened and pictured the entire function which comes in four networks ( page 2-4) as you can see on page 4 the #out3 reads 28 

My question is why is that? I think they should be the same, right? and please note that representation values are in auto option; I can change and choose decimal, hex or floating-point 

Thank you very much in advance

the quality might be low as I had to compress the pictures 

Hello Saed,

let me try to explain how you get OUT3 to be 118.519

Your PIW506 is 16#8000 which is equal to 32768 and it's stored in TEMP6.

Your 3rd network calculates the scale range, in your case upper limit 100 and bottom limit 0 so 100-0=100 and it stores it in TEMP7.

In last network we have formulas :

TEMP 8 = 27648 / TEMP 7

TEMP 9 = TEMP 6 / TEMP 8

OUT 3 = TEMP 9 + IN1 (LOWER LIMIT=0) so OUT3 = TEMP 9

Results:
TEMP 8 = 27648 / 100 = 276.48

TEMP 9 = 32768 / 276.48 = 118.51

OUT 3 = TEMP 9 = 118.51

Hopefully this was helpful.

Thank you very much indeed Mr Lacpa for your thorough response and clarification 

The thing that confused me is that when I monitor it shows me calculations besides each varible i.e  #out3 is 30 !! so what these numbers mean!  

Last but not least what about the (-); it shows -118! instead of 118 

I really can't thank you enough for your response 

forward to hearing from you 

You are absolutely right. Your correction (-)  comes in line with what In have in #out3 

but when I convert  8000 Hexa to decimal the result was (+) as Mr lappa stated, although the result contradicts with the out3

In any way 8000 is that invalid value and that is why the HMI show ####, I wonder 

Apology as my questions might sound simple but am working without any elect drawing as this piece of development has been added recently but the manufacture left without handover due to security issues in Libya 

Hey Saed,

reasoning behind 30 in OUT3 is probably due to monitoring FC4 that is being called somewhere else.

You should go to cross references and see where FC4 is being used.

If you right click on FC4 where it shows 118.51 (Network 12) while monitoring and click open block does it still shows 30 in OUT3 or 118.51?

#### in HMI could be one of two reasons :

1. invalid formatting : numbers of digits, type (real,int,bool), and maybe invalid text box size (try increasing it)

2.incorrect connection between HMI tags and PLC tags

Hopefully this was helpful

thank you for your response

Yes the #out3 is also called in FC40 where it moves data to the HMI I believe and there shows -118

I don't think the problem #####  is the incorrect connection between HMI and S7 as I have all the readings correctly apart from these transmitters and other few things

sounds the 16#8000 is invalid value as it gives negative value as a result 

I will try to simulate the PIW506 via the S7 (enabling simulation ) or hardware and see really confusing when working on a ladder without any descriptions or comments! let alone no electrical drawings daunting! 

Thank you very much 

Hi Saed,

If you want you can attach the program here.

That would make solving problem so much easier.