ATS SPC version 4.0 can operate in a secure data storage regime where data is signed as it is entered and any attempts to change it can be detected. This is achieved by adding the current user ID, and time and date, to each database record and then calculating a ‘hash value’ from the record. The hash value is stored in the database with the record to which it belongs. Any attempt to change the record will result in the hash value calculated from the new data being different to the original and ATS SPC will warn you that your data has been tampered with.
When you create a new database ATS SPC asks whether you want a signed or unsigned database. If you choose unsigned, ATS SPC operates freely and does not implement data signing. Databases from earlier versions of ATS SPC are unsigned when converted for use by ATS SPC version 4.0.
If you create a signed database then ATS SPC operates under the following regime…
· When a batch is created it must be signed before you can collect data into it. In fact ATS SPC does allow you to enter data so you can test the batch and ensure that all features have the correct measuring instruments assigned and all expressions work as intended. Data entered into unsigned batches is not saved however. ATS SPC discards it when you close the batch. See on page 41 for details.
· Once you have signed a batch for data entry you cannot change it again in Design Mode. This means you can’t add or delete features, you can’t change tolerance limits and you can’t change the batch view. If you need to make such changes you must create another batch and continue data collection in that instead.
· All data is signed as you enter it. See What Happens When You Enter Data? on page 68 for details.
· Any data that you delete is simply marked as deleted but retained in the database for future reference. See Deleting Data on page 69 for details.
· You cannot project new control limits back over existing data. See section Running a Batch/Control Limits on page 81 for details.