Lots of questions in one post.

Temporary variable?  You mean inside an FB as a temp tag?  Those are often difficult to see in a watch table (I think it is never, but others may have better luck).  Use a regular tag if you want to monitor.  Also, just be sure and download your changes just to be sure.  If portals says the plc is the same, you did it already.

In the norm/scale for the s7-1200, you can get any values you want out once you normalize the input.  You can have in 0-100%, in engineering units, in user units, or whatever makes sense.

If you need anything other than linear scaling, you have to write your own scaling function.

If you need a table of values, you can create arrays and populate the values as their "start" values.

If you have an array of "xy_values" where xy_values is a user defined type of x value and y value, both floating point, then you can access the values and they stay paired together if you need to loop through the array or grab a set of values from the array.

gerard32

hello...........,

that scaling thing is working now, thanks

i created "level_1_norm"  and "level_1_norm1"  as an temporarly variable.  but how is it possible that when i load the program into plcsim and monitor these values while using the potentiometer the values remain 0 while the rest of the program is working as it supposed to be. i can not monitor the values

 i also used the round function to get a number without decimals. 0-100

perhaps its difficult to explain what i want.  but once i saw an scada aplication in which they used what i use as "#level_scaled" (0-100).  to other values. now 0 to 100 is linear. but what if i want exponential how does that works in siemens.

or more complicated lets say 0-100 is X and i want for every individual X value an specified Y value. like in a table, for example  X2= 5   X3=10  X4=14  X5=19   X6=22.  i managed to get what i want with a lot of comperators and stuff,  but is it also possible to create an table

gr gerard

mareq

 Hi William its me again :). I  use connection like you show us in picture but i use 100K and 140K resistor. My problem is when I connect it to AI0 and 2M voltage decrease from 9.9 V to 6.2 V. So it means that i can control voltage by potentiometer from 0V to 6.2 V but I dont know why... when I disconnect cable from AI0 and 2M I control voltage from 0V to 9.9V again....

I use internal 24VDC from PLC S7-1200.

The "resistance" that you get from the PLC is giving a bit of a problem now because of the selection of the high resistor values.

Use Ohm's law to see how much influence the one has on the other.
You have 6.2V as a reading, so its ( 24V - 6.2V ) over the 140kohm resistor.
Calculate the current from that - I'll call it I1.

Now I1 flows through the resistor that is the combination resistance of the 100kohm and the resistance seen from the PLC. Let's call that resistance R1.

So
R1 = V1 / I1 = 6.2V / { ( 24V - 6.2V ) / 140kohm }

Now we know that     1 / R1 = 1 / 100kohm + 1 / R@PLC

By this mathematical way you can get to the resistor value seen in the PLC which will influence the circuit if it is close to the resistor values of 100kohm and 140kohm.

Now you can use smaller resistors or calculate new value for 140kohm or change the 140kohm with a variable resistor that you can tune. The first is the best option... with the PLC resistance close to the other components values it will continue making an influence.

My previous example worked well enough as the big resistance gap between PLC and potentiometer ensured that the PLC did not influence the circuit too much (but it does!):

1/R1 = 1/R(POT) + 1/R(PLC)
     = 1/10k    + 1/100K
     = 1/0.00011
  R1 = 9.09kohm

 Helpful in understanding the issue?
w