SAP QM – Maintaining Tolerance values for MIC’s in percentage using Specification determination rule
A couple of months ago, I posted a question inquiring how to maintain tolerance values for MIC’s in percentage. Here is the link to the question –
Brief gist about the question: For a quantitative characteristic, let’s say ‘Length’, has target value ‘X’ mm and upper and lower tolerance limits are ±5% of target value ‘X’. How can this (±5%) be maintained in SAP?
In conventional way, we maintain target value and upper/lower tolerance values in Quantitative Data within MIC (or even in Inspection Plan). But when we have tolerances in %, the ‘%’ unit of measurement (UoM) for Tolerances needs to be declared somewhere. At first, my guess was, this can be done by defining Tolerance Key with unit of measurement as % and assigning upper/lower tolerance values in Tolerance Key and then assigning the Key to MIC. Unfortunately, SAP only allows assignment of Tolerance Key to MIC if both MIC and Tolerance Key have same UoM.
As I did not receive much response on my question from peers, I explored further in system myself to see is there is any other way this can be done. Defining Tolerance values for characteristics in percentage is a very normal practice in manufacturing industry and SAP failing to integrate such a small but important function in QM doesn’t really seem acceptable/believable to me. My speculation wasn’t wrong and SAP does allow defining Tolerances in % in QM by using standard SAP ‘Specification Determination Rule’ in MIC.
Following is a brief explanation on how Specification Determination Rule works. The configuration can be split-up in two steps:
- Configurating Specification Determination Rule
- Maintaining Target value
Step 1 – Configurating Specification Determination Rule
The function ‘Specification Determination’ rules are available in Master Inspection Characteristic.
Select the Rule ‘001 – Tolerance Specification in Percent’ to define tolerance values in percent.
Once this rule is selected and set active, maintain the percentage tolerance values in upper and lower tolerance fields under Parameters in Specification Determination function.
Step 2 – Maintaining Target value
Once tolerance values are set, target value must be maintained. Now this is important part. While working with Specification Determination Rule, the value that is entered in Target Value field MUST also be maintained in both Upper and Lower Limit fields, either in Quantitative Data within MIC, or in the Inspection Plan where MIC with active Specification determination is assigned.
The reason behind maintaining the Target values in Upper/Lower Limit field is that the System calculates the actual tolerance values during Inspection Lot creation. So, the system evaluates the actual upper/lower limits during Inspection Lot creation as follows-
Actual Lower Limit = (T1)% × Target Value (maintained in Lower Limit field)
Actual Upper Limit = (T2)% × Target Value (maintained in Upper Limit field)
T1 and T2 are the percent Upper and Lower tolerance values maintained in specification determination rule. (In above example, T1 = -10% , T2 = 10%)
If the Quantitative Data is maintained within MIC, the simulation button in Specification Determination rule allows user to simulate the calculation of actual tolerance limits from % values. Click on simulation button on extreme right next to ‘i’ information button.
Note – The Specification Determination Rule works only when target value maintained in both Upper and Lower Limit fields is same. Otherwise, the Specification determination rule will not work, even if it is active. In that case, the system will read and display the values entered in Upper and Lower limits as actual tolerance limits in Inspection Lot.
This is useful when same characteristic is assigned in different Inspection Plans and has different quantitative data. For instance, in one inspection plan, the tolerance limits are to be calculated in %, and in another inspection plan, the tolerance limits are fixed set of values. In such scenario,
- The Specification determination rule can be set active in MIC and % tolerance values can be maintained in Parameters under specification determination rule function.
- Target value and Upper and Lower limit values can be maintained directly in respective Inspection plans. For inspection plan with tolerance limit calculation in %, target value will be maintained in three fields. For inspection plan with non-percent tolerances, the exact values should be entered in Upper/Lower Limits field. As these two values will be different, system will not execute Specification Determination Rule and just read values in Upper/Lower limit fields as actual tolerance limits.
- This blog describes how Tolerances for Quantitative MICs can be entered in percentage with the help of Specification Determination Rule.
- It describes steps in maintaining percentage Tolerance and Target Values for the Specification Determination Rule to work sucessfully.
Feedback/questions/suggestions are welcome. Please feel free to comment.