Watlow MLS - Manual (Page 126)

114 MLS User’s Guide
Troubleshooting
If you use the Black Box RS-485 interface, make sure you have set it up
correctly. (See the Communications section in Chapter 2 for RS-485
setup instructions.) The LEDs on the unit should blink, but should not
stay lit. For either type of interface, you can connect an oscilloscope to
the transmit or receive line to see whether data is being sent or received.
If the serial interface does not function, contact your computer service
representative.
Communications Problems
If you are experiencing communications problems, check the
communications interface, cables, and connections.
NOTE
Most communications problems are due to incor-
r e c t w i r i n g o r i m p r o p e r c o m m u n i c a t i o n s
parameters. Therefore, check the wiring and com-
m u n i c a t i o n s p a r a m e te r s b e f o re y ou c h e c k
anything else.
If your system has multiple MLS or other control units, you must use
RS-485 communications. Therefore, the internal RS-232/RS-485
selection jumper must be set to the correct position.
From the setup menus, make sure that the communications parameters
(address, error checking and baud rate) are set correctly for each MLS in
your system. Every controller must have a separate address, starting
with 1 and increasing by 1 for each controller. After you assign the
controller addresses, you must configure ANAINSTL with the same
parameters.
In multiple controller systems, ANASOFT indicates which controllers
are communicating and which are not. If you power down a controller in
a multiple-controller system, ANASOFT should indicate a COMM
FAILURE in that unit. Disable communications to that unit until you
power it up again.
Ground Loops
During installation, sometimes the MLS-PM common wire is tied to
earth ground, and the computer's RS-232 common wire is tied to earth
ground. This arrangement creates a ground loop which may affect
communications and other MLS functions. To avoid ground loops,
either use an optically isolated communications adapter or disconnect
the MLS from earth ground and tie an 0.1 microfarad capacitor from
MLS DC common to earth ground.