Complex Math Problem, Atleast to me

[MATT116]

RSLogix 5000 V24
1756-L72

Trying to figure out the best way to solve this problem.

TCF = e ˄ 1100(1/298 - 1/T)

Where T = °C + 273.15
TCF Temperature Correction Factor

I'm not sure why when I divide 1/298 I get 3.35570471e-003 and not 0.003355704

I have ladder, function block and structured text at my disposal.

Thanks

 

[dlweber]

Those two numbers are the same the first version is in scientific format (possibly engineering) the second is in standard decimal.

To get decimal from scientific move the decimal the amount of places and direction specified in the exxx that represents 10^x so e-003 means

3.3557047 * 10^-3

 

[dlweber]

Scientific format is useful to display very large numbers or very small decimals.

Most programs do not recognize p, n, u, m, k, M, G (pico, nano, micro, milli, kilo, mega, giga) to remove excess zeros because using these CAN result in ambiguity in the number, scientific notation removes this ambiguity while removing excess 0's

ie 3G = 3,000,000,000 = 3 billion = 3 * 10^9 or 3e9

One thing to watch for not every program will use or recognize the "e (E)" notation

 

[bernie_carlton]

To further clarify, the 'e' in your formula (the base of natural log or 2.718281828) is not the same as the 'e' in '3.35570471e-003' were it means 'exponent' as explained in dlweber's posts.

 

[dlweber]

To further clarify, the 'e' in your formula (the base of natural log or 2.718281828) is not the same as the 'e' in '3.35570471e-003' were it means 'exponent' as explained in dlweber's posts.

Good catch, I had that feeling I missed something important in there.

 

[MATT116]

Thanks guys for the clarification and I understand what your saying
But I still cant seem to get the correct result in the PLC
Assuming T = 298.15 I should have a result of 8.94 but I get 1.0018588 in the PLC

 

[dlweber]

Off the top of my head I don't know without seeing the math being done, however typically (in any programming) order of operations, or a data type conversion at the wrong time is what I have seen and done to have bad math.

 

[MATT116]

Screen shot attached

 

[dlweber]

1.0018588150955565495100727303679

is what I get from the windows calculator doing the formula

I don't have my tablet with my fancy calculator app on it

 

[bernie_carlton]

Use 0.0033557 instead of 1/298. See if that helps.

 

[danatomega]

Using the exact calculation you have in the CPT box yields 1.0018588.
Not sure why you think it should be different. The formula results appear accurate to me...

 

[MATT116]

Use 0.0033557 instead of 1/298. See if that helps.

Made no difference

This is why I think it should be different
298.15 = Degree C + 273.15
or 25 + 273.15

 

[dlweber]

Is the 1/298-1/T supposed to be in the exponent?

In your Wolfram Alpha they are not, in your PLC they are

Double check your formula

One of them is incorrect

 

[MATT116]

Is the 1/298-1/T supposed to be in the exponent?

In your Wolfram Alpha they are not, in your PLC they are

Double check your formula

One of them is incorrect

That's it! Yes the 1/298 -1/t should be in the exponent so the PLC is correct.

Thanks

 

[dlweber]

order of operations number one mistake =) (I have done so many times)