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Join Date: Sep 2009
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PLC Scaling for TC Type T

11/09/2015 11:25 AM

Hi,

Please could someone help me out, Im trying to scale a temperature of -200 to 100 ºC to 0 - 4096 counts..

I want to creat a scale calculator in excel where I place a value in either count or ºC and get a value.

Regards

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#1

Re: PLC scaling for TC type T

11/09/2015 11:28 AM

0-4096 represents a range of 300 deg C.

A count of zero is -200 deg C.

A scaling block within the PLC program will do this in just one rung. The rest is just arithmetic. What's the problem again?

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#2

Re: PLC scaling for TC type T

11/09/2015 11:55 AM

Hire some kid who knows first-year algebra.

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#8
In reply to #2

Re: PLC scaling for TC type T

11/10/2015 9:54 AM

Sounds to me like a PLC programmer who is suddenly faced with his first analog circuit after 10 years of digital only programming. I've seen this first hand, in the field, three times. It is indeed sad to see "pros" struggling so.

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#9
In reply to #8

Re: PLC scaling for TC type T

11/10/2015 1:12 PM

To be fair, TCs are not perfectly linear. Thus the OP's program needs some curve-fitting or table lookup and interpolation.

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#10
In reply to #9

Re: PLC scaling for TC type T

11/10/2015 4:12 PM

See #7

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#11
In reply to #8

Re: PLC scaling for TC type T

11/11/2015 7:00 AM

Now there's a joule of a thought

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#3

Re: PLC Scaling for TC Type T

11/09/2015 5:35 PM
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#4
In reply to #3

Re: PLC Scaling for TC Type T

11/09/2015 7:22 PM

Lyn,

I think the OP is wanting to develop the procedure in EXCEL not programming a PLC.

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#5
In reply to #4

Re: PLC Scaling for TC Type T

11/09/2015 7:30 PM

?

I had this book at one time.

It helped to cure me from wanting to learning more about Excel™

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#6

Re: PLC Scaling for TC Type T

11/09/2015 9:11 PM

Rise then run as fast as you can at least linearly.

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#7

Re: PLC Scaling for TC Type T

11/10/2015 6:23 AM

This document gives polynomial approximations for obtaining temperature from thermoelectric voltage (and vice versa) for most thermocouples:

https://www.omega.com/temperature/Z/pdf/z198-201.pdf

Here are the approximations for the temperature of a Type T, split into two ranges (showing just the first 3 terms for each range).

E is the thermoelectric voltage in μV and t is the temperature in °C

-200°C to 0°C (-5,603μV to 0μV)
t=E x 2.5949192 x 10-2 - E2 x 2.1316967 x 10-7 + E3 x 7.9018692 x 10-10
0°C to 400°C (0μV to 20,872μV)

t=E x 2.592800 x 10-2 - E2 x 7.602961 x 10-7 + E3 x 4.637791 x 10-11

You'll have to work out how to convert your input (0 to 4096) to microvolts.

Have fun!

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HiTekRedNek (1); JohnDG (2); Legolaz (1); lyn (2); Phys (1); PWSlack (1); SHOCKHISCAN (1); Tornado (2)

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