Howdy,
Typically a tensile tester "known value" is just calibrating the load cell.
I know of no "known value" destructive standards for this type of test...
If it helps, you can send out some samples to an outsource lab, then compare sample means to show that your equipment is giving nominally similar values. If your customer also does this test...you may have more overall benefit sending to them, and thus correlating your sites with the customer as well (and it would be free).
HTH