Hi,

Since you want a Alphanumeric code for your Defect ID, I guess using an Autonumber datatype is ruled out. You would have to code for this particualr field.

NOTE : The below logic would have to be in VB syntax. Also this would work only incase you want a sequentially increasing FaultID.

On the Add New Defect event, you would have to write a code which would generate a sequence of number starting with RMS001. Define a static variable Defect ID with value as RMS001. Once you enter the Sequence code, use a Substr method to extract the 001 part and increment it by value 1.
Also you could use a check to ensure that after updation, Defect ID reflects an incremented value.

Now set the value of your User Defined field Fault ID with Defect ID variable.

I presently dont have admin access to QC, but I have tried this and it should work. Do let me know incase of any issues you face.

Cheers...