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Bias in Automatic Test Equipment for electronics modules
I have read through these forums and note that most of the situations discussed for MSA relate to mechanical applications.
Does anyone have any experience with automated test equipment used to measure electronic characteristics? (ie voltage, current, frequency)
My specific concerns relate to bias.
To determine bias, ideally you require a reference sample that can be measured independently and on test equipment. The difference between the two measurements would be the bias.
BUT
The test equipment is made up of a number of items
-Measuring instruments
-Wiring looms/Spring pins/Switching units/Loads
(Used to interface the Device Under Test (DUT) via it’s connector to the measuring instrument)
-PC
(Used to sequence the test routine, control measuring instruments, adjust timing, provide the comms interface to the DUT to control functions)
AND
The DUT has multiple ( perhaps up to 100 ) analog measurements that must be assessed.
SO
If we use a reference sample we are not assessing the system as it will be used in production because
-We need to provide an artificial means to interface the unit to the tester which can introduce errors.
-We need to modify the software to allow the characteristic to be measured.
-We only test one path/function of many
Our bias could end up small, but is this measurement meaningful?
An alternative is to use a production unit.
The difficulty here is measuring the characteristics independently. If you are not using exactly the same equipment ( generally the case ) then of course you will have differences in measurements. Which one is correct? If you assume the independent measurement is correct and now calculate the bias, how do you determine what is acceptable? The QS9000 manual is very vague on numerical acceptance criteria for bias.
Must every step be evaluated in the same way?
I do believe that bias is an important characteristic to measure. You can have a highly repeatable measurement, but if you are not measuring the correct value, with the wrong tolerance stackup you will end up sending faulty parts to the customer.
If anyone has any comments / suggestions that are relevant to my situation it would be greatly appreciated.
Stuart
I have read through these forums and note that most of the situations discussed for MSA relate to mechanical applications.
Does anyone have any experience with automated test equipment used to measure electronic characteristics? (ie voltage, current, frequency)
My specific concerns relate to bias.
To determine bias, ideally you require a reference sample that can be measured independently and on test equipment. The difference between the two measurements would be the bias.
BUT
The test equipment is made up of a number of items
-Measuring instruments
-Wiring looms/Spring pins/Switching units/Loads
(Used to interface the Device Under Test (DUT) via it’s connector to the measuring instrument)
-PC
(Used to sequence the test routine, control measuring instruments, adjust timing, provide the comms interface to the DUT to control functions)
AND
The DUT has multiple ( perhaps up to 100 ) analog measurements that must be assessed.
SO
If we use a reference sample we are not assessing the system as it will be used in production because
-We need to provide an artificial means to interface the unit to the tester which can introduce errors.
-We need to modify the software to allow the characteristic to be measured.
-We only test one path/function of many
Our bias could end up small, but is this measurement meaningful?
An alternative is to use a production unit.
The difficulty here is measuring the characteristics independently. If you are not using exactly the same equipment ( generally the case ) then of course you will have differences in measurements. Which one is correct? If you assume the independent measurement is correct and now calculate the bias, how do you determine what is acceptable? The QS9000 manual is very vague on numerical acceptance criteria for bias.
Must every step be evaluated in the same way?
I do believe that bias is an important characteristic to measure. You can have a highly repeatable measurement, but if you are not measuring the correct value, with the wrong tolerance stackup you will end up sending faulty parts to the customer.
If anyone has any comments / suggestions that are relevant to my situation it would be greatly appreciated.
Stuart