| In these two photos, comparative testing is being carried out between a vector network analyzer and the WireXpert cable tester on prototype Category 8 cables. The specially designed adapters attached to the WireXpert allow the comparison to be done without modifying the connections of the cable under test. |
During a web seminar hosted by Cabling Installation & Maintenance on October 31, Psiber Data's (www.psiberdata.com) managing director Harshang Pandya addressed this situation and provided some detail on TIA-1152. Officially titled "Requirements for Field Test Instruments and Measurements for Balanced Twisted-Pair Cabling," TIA-1152 was published in 2009 and details the capabilities as well as accuracy levels of field test instruments. As Pandya explained during the seminar, "The field testing standard TIA-1152 is very closely tied with cabling specifications. As TIA-568-C.2 is being revised [to include Category 8 specifications], there is effort ongoing to revise TIA-1152 for Category 8 support. TIA-1152 field testing specifications go hand-in-hand with cabling specifications."
Before going into detail on the revision of TIA-1152, Pandya provided some information on what the existing standard is and what it covers. Specifically, 1152 defines the accuracy levels required to test installed Category 5e, 6 and 6A cabling systems. A tester with Level II accuracy can test Category 5e systems, which operate in the frequency range up to 100 MHz. Testers with Level III accuracy can test Category 6 systems, which operate in the frequency range up to 250 MHz; Levell III-accuracy testers can also test Category 5e systems. And testers with Level IIIe accuracy can test Category 6A (500-MHz) system as well as Category 6 and Category 5e systems. The proposed accuracy level for Category 8 (2-GHz) systems is being called Level 2G (apparently in keeping with Category 8's 2-GHz bandwidth).
The characteristics of a test instrument that ensure it can accurately measure an installed cabling system are the essence of the existing TIA-1152 standard as well as its in-the-works revision. Pandya explained that field test instruments must meet certain performance levels for parameters such as dynamic range, measurement noise floor, residual NEXT/FEXT, output signal balance, common mode rejection ratio, directivity and tracking. A tester's ability to meet these prescribed parameters is determined by determining the results a field tester produces, using a vector analyzer as a reference.
The extent to which a field tester meets the aforementioned parameters determines its ability to accurately measure cabling-system performance characteristics including insertion loss, crosstalk and others.
Pandya pointed out during the seminar that meeting the requirements of TIA-1152, or its revision, is just a first step for a manufacturer of cabling field test equipment. "They must confirm the accuracy being claimed by internal test setups," Pandya noted. "Once that is confirmed, the next step is to have an external lab verify that the claim of accuracy is correct." In this process, the third-party lab sends a scientist to the tester manufacturer's facility to verify the accuracy claims. The lab then inspects the manufacturing process, every few months on an ongoing basis, to ensure consistency.
Additionally, Pandya pointed out, from the standpoint of cabling-system manufacturers, much is at stake related to field-tester accuracy. The pass/fail judgment on an installed cabling system is highly significant both in terms of application support and manufacturer warranty. With so much on the line, he said, before approving a field tester, most cabling vendors evaluate the tester in their own labs. If and when the tester satisfies the cabling manufacturer, that manufacturer will approve the tester for the certification of its system. "Cabling vendor approval is the final, important piece in the field tester accuracy process," he said.
The standards developers revising TIA-1152 are in the early stages of determining their specifications. More progress is certain to be made in the months ahead.
Patrick McLaughlin is our chief editor.
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