# Interpolating between two graphs

#### justmcd

##### New member
Hi

I have scatter graphs created from reading taken from one off the books used to design crotch plates ( see attached). I have managed to do interpolation for various dt values at angles given by each graph. However I have a problem interpolating for an angle other than the one given a different degrees (eg. 53 degrees). The ultimate solution that I am looking for is to get dt value for any degree between 30 and 90 degrees.

Regards
Justmcd

#### Attachments

• Crotch plate.xlsm
20.1 KB · Views: 221

#### jpr73

##### New member
Hi,
See attached the expect result of dt value for any degree between 30 and 90 degrees
Hope this will helps

#### Attachments

• Crotch plate_jpr73.xlsm
18.1 KB · Views: 229

#### justmcd

##### New member
Hi,
See attached the expect result of dt value for any degree between 30 and 90 degrees
Hope this will helps

Hi jpr73

thanks for you prompt responce. loooking at you spreadsheet when I change db to 2 inches at 53 degrees, I get N/A. it does not interpolate dt for 2 inches. The example i have for a 2 inches at 53 degree gives out a dt value of 15 inches with the db of 31 inches. the answer does not have to be exact but around 15 inches.

Once again thanks for help.

Regards
justmcd

#### jpr73

##### New member
Hi,
Sorry I misunderstand your post : interpolate in 2 dimensions
See attached the result with any angle and base depth
Note : the formulas are not working for the extreme value of angle and base depth
Hope this helps
Best regards

#### Attachments

• Crotch plate_jpr73_a.xlsm
18.3 KB · Views: 343

#### justmcd

##### New member
Hi,
Sorry I misunderstand your post : interpolate in 2 dimensions
See attached the result with any angle and base depth
Note : the formulas are not working for the extreme value of angle and base depth
Hope this helps
Best regards

Hi jpr73

Thanks a million. You are a life saver.

Thanks once again

Regards

#### aeroarun

##### New member
Hi jpr73,
I need your kind help for a similar problem, please could you tell me how to modify the spreadsheet to interpolate between similar set of curves (centrifugal compressor performance curves . I can upload the curve data which is flow vs head for different speeds (70% -105%) i need to know head for a arbitrary speed and know flow (x-axis).
Thanks and regards,
Arun

#### jpr73

##### New member
Hi aeroarun,
It would be better to create a new post.
Please upload the curve data and formula, I'm not the only one who can solve the problem
Best regards