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The Direct Connect MAG Network
The Direct Connect MAG Network includes one MAG Panel and one absorption chiller unit
controller. In this case, the MAG Panel is the level-1 controller and has a hex switch setting of 00.
Since the absorption chiller contains a non-MicroTech unit controller, it does not have a level or a hex
switch setting.
For example, assume that a MicroTech network includes a MAG Panel and one absorption chiller. The
only possible addressing scheme is as follows:
Hex Switch Setting
Controller
00
MAG Panel
Note:
This type of network can connect directly to another company’s building automation system
(BAS) via the MAG Panel’s port A or to a PC with Monitor software.
Connecting the Communications Trunk
Use the following procedure to connect a communications trunk between a Network or Direct Connect
MAG Panel and absorption chiller unit controllers.
Communications Cable Check
The network communications cable should have been installed in accordance with the instructions in
the “Field Wiring” section of this manual. This procedure verifies that there are no shorts or stray
voltages anywhere in the communications trunk.
Before beginning, verify that the port B connectors are disconnected from every controller on the
trunk and the CIC cable is disconnected from the absorption chiller unit controller.
1.
Verify that there is no voltage between any conductor and ground.
Use a voltmeter to test for voltage at the field wiring terminal block or directly on the port B
connector of the level-1 controller. With one lead on the control panel chassis (ground), check for
voltage at the “+,” “–,” and “ground” terminals. There should be no AC or DC voltage (see the
Signal and Terminal columns of Table 9). If the conductors are properly terminated, this check
tests for stray voltage throughout the trunk.
Note:
If you get a 2 or 3 Vdc reading, it indicates that one or more powered controllers are
connected to the trunk. These controllers should be located and disconnected.
2.
Verify that there are no shorts between any two conductors.
Use an ohmmeter to test for shorts at field wiring terminal block or directly on the port B
connector of the level-1 controller. For the three combinations of conductor pairs, there should be
infinite resistance between the conductors. If the conductors are properly terminated, this check
tests for shorts throughout the trunk.
Note:
If you find a resistance that is high but less than infinite, it indicates that one or more non-
powered controllers are connected to the trunk. These controllers should be located and
disconnected.
3.
Verify that the communications wiring is continuous over the trunk and that the field terminations
are correct. (This step is optional but recommended; to do it, you must know the physical layout
of the network's communications trunk.)
Go to the last controller on one end of the daisy-chain and place a jumper across the "+" and "–"
terminals. Then go to the last controller on the other end of the daisy-chain and use an ohmmeter
to test for continuity across the "+" and "–" terminals.
Remove the jumper and repeat this step for the other two conductor pairs: "+" to "ground" and
"–" to "ground."
