Macro PDF417 barcode symbols are used on Mil-Std-129 labels when the number of IUIDs exceeds the capacity of the standard PDF417 symbol. Both are effective ways to communicate the Unique Identifiers (UIDs/IUIDs) of items in a container, as well as the associated identification text such as contract, NSN, etcetera.
The maximum number of UIDs that can be included is limited by the permissible PDF417 size. This problem has been resolved in the past by listing excessive UIDs on separate barcoded serial number lists.
The use of Macro PDF417 barcodes for Mil-Std-129 containers solves the data limit problem by using multiple PDF417 barcodes to include all the UIDs. When read by specialized scanners and/or scanning software the data in the barcodes are stitched together, as if collectively they represented one large barcode. The symbols may be read in any order and/or repeatedly, making it easier for an operator or automated system to gather up the information. They are simply scanned until all have been read.
The use of the Macro symbol is not limited to UIDs. It also applies to containers with just serial numbers. Simply stated, anytime a PDF417 symbol is specified but unable to contain the data, one or more Macro PDF417 may be substituted.
Mil-Std-129R does not specify the layout of formats that use the Macro PDF417 symbols or provide any examples. It simply states that the UII(s) should be encoded in a single PDF417 or the Macro symbols. No specific illustrations of the symbols in container labels are provided. Some additional direction is provided:
- The 2D bar code(s) shall be placed in close proximity to the identification marking.
- The bar code(s) shall be preceded by a data area title for the encoded information, for example “ID DATA INCLUDES UII(s)”.
- Instructions indicating that the symbols may be scanned/rescanned in any order are included by way of example, but with the language not otherwise specified.
The exterior container label illustrated above is Mil-Pac’s implementation of the requirements. See full size example (PDF).
The use of the Macro symbols to communicate a large number of UIDs and/or serial numbers can be very useful. However, because it requires specialized scanners and/or software, the data may not be readily accessible in all circumstances. The use of barcoded serial number lists can provide redundancy in such cases, but only if they include the serial numbers in the clear and linear barcodes along with stand-alone PDF417 symbols listing the Unique Item Identifiers (UIIs).
Serial Number Lists
The requirement for barcoded serial number lists applies to containers labeled with Macro PDF417 symbols. The use of barcoded serial number lists resolves some of the limitations inherent in use of the Macro PDF417:
- Reading Macro PDF417 barcodes requires specialized barcode scanners and/or software.
- The container does not have to be present to process serial number lists.
- Serial number lists persist after the container has been unloaded and discarded.
Mil-Std-129R does not precisely specify the requirements for barcoded serial number lists. Defense contractors may want to consider inclusion of the data in three formats:
- Serial numbers in the clear and in linear barcodes
- UIDs in standalone PDF417 symbols separated into groups small enough to be encoded
- Summary Macro PDF417 symbols listing the UIIs within a container
The use of the Macro symbol allows the barcoded serial number list to provide the same robust data that appears on the Mil-Std-129 container label independently of the container and after the units have been removed from it.
Coordination of Multiple Label Sets
The data set for a container may require Macro PDF417 symbols printed on several labels. This can be confusing when multiple containers are being labeled. Matching labels to containers may even be confusing even where there is a single label per container because the UIDs are not listed on the label.
A container identifier, printed at the bottom of the label, can be used to solve this problem. For example, Mil-Pac uses an identifier that looks like 00017AA-001/2 at the bottom of each label to identify it. The identifier is of the format: <CLIN> – <Container Number> / <Label Number>, where:
- Container Number – a sequential counter of containers used for the CLIN.
- Label Number – ‘1’ is the primary label and ‘2’ and beyond are its overflow labels.
For RFID-tagged labels the first label of each container will show the RFID tag, and the overflow labels will reference the last four digits of the RFID tag in place of the Container Number:
|RFID CASE 2F12031484C4439000002A0B7
0019AA-A0B7/n (where n is Label Number)
Challenges of Using Macro PDF417 Barcodes
There are distinct challenges in the use of labels with Macro PDF417 symbols, both for the producer of them and their consumers. Producing the symbol requires handling of the Mil-Std-129 compliant data structure which stretches across multiple symbols, and in the extreme, multiple labels.
A more substantial challenge is reading these labels. Software systems designed for the standard PDF417 symbol expect to see a complete Mil-Std-129 data structure in each barcode’s payload. The Macro PDF417 symbols appear to be incomplete to such systems.
It is possible to scan a set of these symbols to a text editor and extract the data manually, but that is an tedious task. Effective solutions fall into two categories:
- Specialized scanning software that can pick up the symbols, which may be read in any order and multiple times, and stitch together a result that is compliant with the data structure defined by Mil-Std-129.
- Specialized scanners that can do the same thing internally and produce a result that appears to be the scan of a single label.
Software systems that consume such data must be able to accommodate data that is considerably larger than that produced by scanning a UID container label barcode with a single standard PDF417 symbol.
Radio Frequency ID (RFID)
Mil-Std-129 requires that UIDs be included in the PDF417 symbol included on container labels. However, the effectiveness of that approach is limited by the space available in PDF417 symbols and the reliance on barcoded serial number lists for containers with more than five items. RFID helped solve that problem by requiring that a manifest be uploaded into WAWF, detailing the UIDs loaded into each container by its RFID tag. Unfortunately, use of such data requires access to business systems, which can be a challenge, especially in the field.