Micromod MOD: MODCELL Multiloop Processor 2002N Model C and Associated Hardware - Manual (Page 32)

MODCELL Multiloop Processor
ELECTRICAL CONNECTIONS
3.4.2 Shield Ground
The shield terminals, Figure 3-1, are only connected to one another; they are not
internally connected to chassis ground or circuit common. Two brass jumper straps are
included with each processor to connect chassis ground and/or circuit common to the
shield terminals. Failure to make these connections renders all shield connections
useless. When installing the jumpers consider the following:
• For most applications, one jumper should be installed to connect terminals A and B to
SH1, and the second jumper should be installed to connect terminals C and D to SH8.
• If the application requires that chassis ground (terminals A and C) or circuit common
(terminals B and D) should not be connected to the shield terminals, the jumper straps
can be modified as shown in Figure 3-1 to provide the required connections.
For example, to connect terminal A to SH1 break away the center post by bending it;
to connect terminal B to SH1 break away the end section and post at the etched line.
3.4.3 Circuit Common Interconnection
The circuit commons of all processors on a network should be connected together. Use
either terminal B or D to make the connection.
The interconnection of the circuit commons prevents the processors from floating with
respect to one another. This interconnection is in addition to the circuit common
connection in the ICN.
3.4.4 Electrical Noise
Electrical disturbances can be caused by lightning, motors and motor driven devices,
relays, solenoids, and communication equipment. These disturbances often introduce
electrical noise in power lines, transmission lines, and site grounds. The successful
operation of any microprocessor-based device depends, in part, on the precautions taken
to minimize the effect of these disturbances. Often called "transients" or "voltage spikes"
this form of noise is infinitely variable in terms of amplitude, frequency, and duration.
Common sources of this type of noise are:
•
loose or poor quality connections (especially power connections)
• arc welding equipment
• switches operating inductive loads
• relays, solenoids and other coil operated devices
• high current conductors – electric heater circuits
• fluorescent or neon lamps
• motors and motor driven devices
• switch mode devices – SCRs, thyristors
• lightning
• electrostatic discharges
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