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advanced scaling: complex equation or large scl

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advanced scaling: complex equation or large scl

Postby mallpall » Thu Feb 06, 2014 9:41 am


I am trying to integrate a scaling in to my input channels.

The goal is to read out a NTC, this thermal resistor has kind of logaritmic function.(See attachment)
It is very important to make almost no fault on the scaling.

I tried to make a scaling file:
50 0.04
and 1000 more of these rows"
Picolog crashes when i try to use this large scaling file, with small files there is no problem.
Is there a solution to use large scaling files?

On other solution, could be making a equation with multiple interval.
An example: if 10<X<30 then 30*ln(x) else -10<x<10 then 10*ln(x)
Is it possible to use this kind of programming in the eqaution input?

thank on advance
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Re: advanced scaling: complex equation or large scl

Postby PeterF » Tue Feb 11, 2014 11:07 am

Simple Look-up tables have a limit of around 14 lines, above that, use a "Scaling File" but even a scaling file has a limit on the number of lines but I do not have details on t he number. I think it varies on the logger used. You will need to experiment with how many lines you can actually use. You will certainly not need to use 1,000 lines, a lot less will be perfectly adequate. PicoLog interpolates between values.

If you use a scaling file you must ensure that either:-
1. All parameter formatting is done on the parameter formatting page only and none in the scaling file (just the equation or look-up table).
2. Parameter formatting is NOT ticked and all formatting is done in the scaling file only.
Duplication of parameter formatting will cause a crash!

Unfortunately, a complex equation cannot be used either.

I have calculated an example scaling file for a 15kohm thermistor and the PicoLog 1216. Use a 15kohm surface mount load resistor in position R33 on the terminal board. Connect the thermistor between the channel 1 input and ground (gnd). (Neither R1 nor R2 are used):-
http://www.picotech.com/document/pdf/DO ... uide-3.pdf

Start PicoLog and set-up your sample rates as required.
When you get to setting up Channel 1 ("PicoLog 1000 Channels"), highlight "Channel 1" and click "Edit".
Type "Temp Chan 1" as the Name.
Now click on "Options". (You might be asked to save the present setup, click "OK").
In the "Parameter options" dialogue, select "Scaling".
For "Scaling method" select "Use scaling from file" and click on "File".
Navigate to where you have saved the scaling file (that you have made earlier!), "15k thermistor.scl".
Open the file. Click OK several times to get back to the main PicoLog window.
You should be reading temperature on channel 1.
Please contact me again if you have any other questions.

Scaling file contents (15k thermistor.scl):-

2.372 -40
2.342 -35
2.304 -30
2.257 -25
2.200 -20
2.131 -15
2.051 -10
1.959 -5
1.855 0
1.743 5
1.622 10
1.496 15
1.368 20
1.241 25
1.116 30
0.998 35
0.887 40
0.784 45
0.691 50
0.607 55
0.531 60
0.465 65
0.406 70
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