By means of the ATP quantity (available to promise), the MRP controller can determine if all issues are covered by the master plan and how much of the receipt quantity is still available for new issues.
During the ATP quantity calculation, therefore, the system checks that all issues are covered by existing receipts and whether quantities are left over to cover new issues. These quantities that have not yet been allocated form the ATP quantity. In detail, the calculation is made as follows:
- The issues (customer requirements, planned independent requirements reservations) are dynamically allocated to the receipts (warehouse stock, planned orders, purchase requisitions and so on) which lie directly before them. The calculation is carried out in such a way that the issue is is allocated to the receipt which lies nearest to it and which still has a positive ATP quantity.
- If the ATP quantity of this receipt does not cover the issue then the system will search for and check the next nearest receipt (always in a backwards direction) for a positive ATP quantity which will then also be allocated to the issue.
If the issue cannot be covered by existing receipts then the production plan has to be changed. This means that new planned orders or purchase requisitions have to be created.
In contrast to the calculation of the ATP quantity, the system determines available quantity by adding or subtracting the quantity of goods received or the issue to/from the planned warehouse stock for each MRP element.
See the following example for more information on calculating the ATP quantity:
The issue of the 10/6 for 50 pieces is allocated the receipt of the 10/5 for 100 pieces. The ATP quantity of the receipt is then 50 pieces.
The issue of the 10/15 for 100 pieces is allocated the receipt of the 10/13 for 200 pieces. The ATP quantity of the receipt is then 100 pieces.
The system allocates the issue of the 10/16 for 200 pieces with the two previous receipts as no further goods receipt has since been carried out.
The ATP quantity of the 10/13 which amounts to 100 pieces is firstly allocated to the issue. The ATP quantity of this receipt is then 0. At this stage, the issue is still short of 100 pieces. Therefore, the ATP quantity of the 10/5 for 50 pieces is also allocated to the issue.
The new ATP quantity for this receipt (10/5) is now also zero.
However, the issue of the 10/16 is still not completely covered and is short of 50 pieces. Additionally, you receive an exception message indicating that the master plan does not cover all the issues.
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