Johnson Controls 300 Series Manual page 65

Network Control Module 300 Series Technical Bulletin
• Use these methods to check the termination LAN resistance:
- If the Network consists of NCM101/401/200 series controllers
and high DC resistance ARCNET cards, power down the
network and, with the LAN cables connected, insert a
T-connector and measure the conductor-to-shield resistance.
The value should nominally be 46.5 ohms, with an acceptable
range of 46 to 54 ohms. If properly terminated, it does not
matter how many NCMs are online. Readings less than
46.5 ohms indicate that more than two terminations are on the
LAN. A reading of 93 ohms indicates that only one termination
is on the LAN. N1 LAN confidence-level tests are found in the
Network Communications, JC/80 Coax on N1 LAN Application
Note (LIT-6363142).
- If the network contains low DC resistance ARCNET cards
such as the NET101, then these nodes must be disconnected
prior to making the resistance measurement indicated above, or
the value measured is lower (1 to 54 ohms).
- If available, use a time-domain reflectometer to estimate where
a problem or discontinuity exists.
- As a general N1 termination check, the outside conductor must
be isolated from the earth ground for proper operation. Test N1
connections (including barrel connectors) for possible shorts
from the outside conductor shield to ground. The resistance
should be in the Mega-ohm range.
VMA14x0 Controllers Cycle Online and Offline
VMA14x0 controllers cycle online and offline when remotely
connected to an NCM via an S.I. Tech™ 2110 Optical Asynchronous
Mini Bit-Driver® modem with a serial number lower than 044301.
This problem is specific to the AP-VMA14x0 controllers. Devices
communicating via N1 are not affected. To solve the problem, order a
replacement with serial number 044301 or higher from S.I. Tech at
www.sitech-bitdriver.com. If you received an old style S.I. Tech
Bit-Driver as part of a new construction order, contact
Johnson Controls for possible credit.
65