Many times I've gotten call's from customers saying their data company pulled new Ethernet cables and now one of the MS/TP comm buses on their Niagara-Ax Jace is not communicating at all. Before getting out my laptop, I get out my Fluke multi-meter using these steps to isolate the problem.
With your multi-meter set to ohms.
Step 1: Remove ground/drain wire from Niagara-Ax Jace comm plug.
Step 2: Place meter leads black lead on the drain wire and the red lead to earth ground .
a: 3 ohms and above shield not grounded at all.
b. less than 3 ohms grounded in more than one place.
c: 0 ohms is normal reading
With your multi-meter set to DC check comm bus.
Step 1: Place red lead on positive terminal and black lead on negative terminal of the Niagara-Ax Jace comm plug.
a: below 200 MV wires shorted.
b.200 MV normal
c:above 500 MV one side is not connected.
Check for miss wired net/communicating sensor, from com bus.
Step 1: Place red lead to comm bus + terminal on the Niagara-Ax Jace the black lead to earth ground.
Step 2:Place red lead to earth ground and the black lead to the - negative terminal on the Niagara-Ax comm plug.
a: 2 to 2.5 MV normal reading
b: 3 to 12 MV net sensor miss wired or shorted
c: less than 700 MV short to shield
Change multi-meter to AC
Step 1: Place red lead to comm bus + terminal on the Niagara-Ax Jace the black lead to earth ground.
Step 2:Place red lead to earth ground and the black lead to the - negative terminal on the Niagara-Ax comm plug.
a: 2 volts is normal
b: greater than 2 volts bad or miss wired controller putting voltage on comm wire
c: less than 2 volts short in comm wire,
If you get bad read from any of the test,You'll want to deploy the divided conquer method to track down the issue.
Step 1: Go to the middle of the MSTP bus and remove the comm bus from the controller. The check voltage and ohms on both wires to locating the bad wire.Leave comm bus wires separated.Go to step 2
Step 2: Go to middle of bad the wire, split trunk again.Check voltage and ohms both ways, finding the bad wire.Leave comm bus wires separated.Go to step 3
Step 3: Repeat steps 2 until you find short or bad voltage.
