s7 scaling question

darren.s · May 5, 2005

hello people

im after some help with the scaling of an analogue input with s7.
if i have a pressure tansducer 0-400 bar at 4-20ma and the input card is configured correctly.
12bit card.
assume signal comes in to PIW256 im after some help on how to manipulate this figure so i can make sense of it and use it in the program for different tasks.
is it best to leave the figure as is and use compare functions.
to flag alarms for example?

SimonGoldsworthy · May 5, 2005

Assuming S7 300/400 series, use FC105 to scale your analogue signal into engineering units, see example below: (wFC105Return is a word variable, rPressureInBar is a real variable)

CALL "SCALE" (
IN := PIW256,
HI_LIM := 4.000000e+002,
LO_LIM := 0.000000e+000,
BIPOLAR := FALSE,
RET_VAL := #wFC105Return,
OUT := #rPressureInBar);

darren.s · May 5, 2005

cant seem to get my head round this real number syndrome.
4,000000e+002 and 0.000000e+000 as above.
can anyone explain these figures i know "e" is the exponential but im just not getting it.

kamenges · May 5, 2005

One of the examples above:

4.000000e+002

can be expressed as 4.000000 * 10², or 400.
The basis for the exponent is assumed to be 10.

So in a generic sense:

x.xxxxxxe+yyy

is x.xxxxxx * 10^yyy

Hope this helps.
Keith

darren.s · May 5, 2005

i understand that 4*10 to power of 2 is 400 which = 4.000000e+002
but why express all the 000000,s why not 4e+002.
am i missing something here!
maybe i should just give up

SimonGoldsworthy · May 5, 2005

The display format for the numbers is a function of the Step 7 block editor. When creating the code, I actually typed "400.0" and "0.0", but the editor then displayed the numbers in the generalised floating point format.

darren.s · May 5, 2005

makes sense now thanks alot!

Amr Hassan · May 8, 2005

try this

L #input_channel
ITD
DTR
L 2.764800e+004
/R
T #percent

L #span
L #zero
-R
L #percent
*R
L #zero
+R
T #reading

L #hi_setpoint
>=R
= #hi_alarm

L #reading
L #hihi_setpoint
>=R
= #hihi_alarm

s7 scaling question

darren.s

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SimonGoldsworthy

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darren.s

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kamenges

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darren.s

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SimonGoldsworthy

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darren.s

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Amr Hassan

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