Excel Help for a Numpty!

[barryuk99]

Hi All, I thought I was reasonably ok with using Excel, but have a total mental block with this seemingly simple issue!

I'm using Excel to calculate the percentage of a certain gas in a mixed gas input into a chamber.

So when inputting 10 Standard Litres per Min (SLPM) using a 5% to 95% gas mix. The 5% quantitiy in Standard Cubic Centimeters Meters (SCCM) can be calculated by using this Excel command
"=SUM(A2*1000/100)*5".

Now all I want to do is write a command line that will calculate how much I need to increase the 95% gas flow, to reduce the 5% gas flow to a 3% ratio mix.

I know that the answer to this is that the flow needs to increase to 16666 SCCM, but dont know how to write the Excel command?

Thanks in advance.

 

[Martynt74]

Perhaps i'm being stupid (very likely), but if you're reducing the 5% element down to 3%. Would the 95% not just increase to 97%?

Also if you're reducing from 5% to 3% would the SCCM not reduce?

 

[barryuk99]

Many thanks for your response. There's some info I should have included. The 5/95% gas mix is fixed and I need to add an additional gas to reduce the ratio. So, using an Excel formula I'd like to calculate the addional gas required from a separate gas line.

 

[namnoc]

If you are adding a second 100% gas at flow rate Y then the percentage in the mix is given by:

%age = (10 * 0.95) + Y)/ (10+Y)

So to get 97%

0.97 = (9.5 + Y) / (10 + Y)

9.7 + 0.97 x Y = 9.5 + Y

0.2 = 0.03 x Y

Y = 6.6666666

 

[barryuk99]

MANY THANKS namnoc. That worked a treat.