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The Model ST123 has been shipping for several years. It performs a
pin-to-pin continuity and shorts test and what we call an integrity test
that assures that SCSI signal pairs are connected to twisted pairs in
the cable. The ST123 has an LED indication of faulty pins in the
continuity test and of faulty pin pairs in the integrity test. We assume
that the cable assembly is made with cable that meets the SCSI
specifications for impedance, shielding, twisted pairs, etc. The ST123
has connectors for testing cables with 50-pin high density and 50-pin
Centronics type connectors as well as the 68-pin high density. We offer
an adapter for testing of cables with one or two 68-pin VHDCI
connectors. Other than plugging the ST123 into a power line, there is no
set up required and a SCSI cable assembly can be tested in a few
seconds.
The Model ST1000 Handheld SCSI Cable Tester is a “pass/fail” tester
introduced in 2003. Like the Model ST123, this device makes continuity,
shorts and integrity tests. However, with the battery operated Model
ST1000, you need plug only one cable connector into the unit and a
“loopback module” onto the connector on the far end of the cable. This
means that installed cables do not have to be removed in order to test
them. That makes it ideal for testing in the field.
In addition to continuity and integrity tests, when connected to a
powered SCSI bus segment the ST1000 will display the presence or absence
of TERMPWR, display the measured value of DIFFSENSE and display whether
the bus is Single-Ended (SE), HVD or LVD.
Also, the ST1000 performs a twisted pair location test to determine
that the critical REQ and ACK signals are not in the outside layer of
the cable. The REQ and ACK signals determine SCSI timing and are quite
susceptible to noise. Assuring that REQ and ACK are in the core or
middle layer of the cable assures that they have the maximum amount of
shielding from outside noise sources. The ST1000 then displays the
suitability of the tested cable assembly for use in SE, HVD or LVD SCSI
bus segments.
The ST1000 has a 68-pin high density connector and adapters are
available for testing cables with VHDCI and/or 50-pin connectors.
A few words about the importance of the integrity test in the testing
of SCSI cables: At the speed that SCSI operates, the cable is an rf
transmission line. As with all rf transmission lines the impedance of
the line is very important in order to minimize the amount of energy
reflected from the receiving device back to the transmitting device.
These reflections can cause many very hard to trouble shoot problems
ranging from a system that refuses to boot to a fault that occurs very
infrequently. It is extremely important that SCSI signal pairs are
assigned to twisted pairs in the cable in order to maintain the
impedance that the cable is designed to meet and to reduce crosstalk to
a minimum. Passing the continuity and integrity tests of Paralan SCSI
Cable Testers assures that the cable assembly is not the source of
problems in your SCSI system.
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Paralan
SCSI