RI Title
RI logo


Purpose: To describe the creation of a fixture offset factor, measured from a golden part, to be used in subsequent test plans. This document will both describe how to generate this offset and how to recover it for subsequent testing. It is also the intent to describe some of the concerns with offsets and the importance of placing limits on their generation and recovery.



Customer Warning - This procedure is not supported or recommended by Roos Instruments. The below procedures are outlined for those customers who have a true need for offset testing. It is always recommended that tester data be correlated to bench data to facilitate offset-less testing.

Theory: Use the Cal Data Save button to store a calculated offset and use the CAL Factor Source button to recover it later in a test plan.

Creation of the offset name
1. Activate the fixture that is to store the specific offset data.
2. With a right mouse button click (RMBC). pull down the fixture menu and request to inspect the fixture calibration.
The Cal table inspection window for the fixture will pop up.
3. Choose "Calibration entry" and then "Add Item". You will be prompted to type in a "new cal entry name".
4. Type in the name and then press "OK".
5. Go back to the fixture icon and from the pull down menu select "Save Calibration". The name of the offset is now
stored in the fixture calibration table.
6. Deactivate and reactivate the fixture. Repeat steps one and two to make sure the offset name was really saved.

Writing the offset test plan
7. Write a cal plan to measure the desired parameter from a golden part. In my example I decided to measure
voltage on VCC3 as set up on DP1. I then compared it to an expected value of 5.5V (System Calc Input button). I
then store the calculated offset into a Fixture Cal Data Save button (Figure 1). The Fixture Cal Data Save button
is created by using a System Cal Data Save button and changing its owner.
8. Since the test plan will calculate and store ANY number in the fixture offset data the test engineer MUST
provide reasonable limits for the fixture offset.

Caution: Failure to provide reasonable limits to the fixture offsets will allow for the
calibrating out of severe fixture or device issues. It is the responsibility of the
customer / user to provide reasonable limits in the use of this offset technique.

Caution: You MUST make sure the desired fixture is active before running. Failure to
do so will add offset values to fixtures left unintentionally active during the
run cycle.


9. Once the limits have been set, the test plan may be run. Figure 2 represents the data measured and the
offset stored in the fixture. Repeat step 5 in order to actually save the offset data.

Test Panel Settings to Generate An Offset


Figure 1

Measured Data and Calculated Fixture Offset

Figure 2



Retrieving a Fixture offset

10. Write a test that uses the Fixture Cal Factor Source button. This button is created using a System Cal Factor
Source button and changing its owner. Figure 3 represents the buttons used in measuring the 5V set on VCC3.
It also shows the offset (Golden offset) being calculated into this measurement to show the "After offset added"
result.

Caution: Make sure the measurement used to retrieve the offset duplicates that used to generate it.

Caution: Make sure the same calculation used to generate the offset is also used in the
final calculation.

Test Panel Used to Retrieve Fixture Offset


Figure 3

Offset Retrieval Results


Figure 4

PrintEmail Link
https://roos.com/docs/RBEH-94FPZR
ROOS INSTRUMENTS CONFIDENTIAL AND PROPRIETARY
©2013-2022 Roos Instruments, Inc. All rights reserved.