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4.0 Trouble Shooting
4.1 Power Problems
Problems on
power up
Unit does not light or unit lights but does not display any
messages.
1. The MMI has a switching power converter in it. If the Power
Supply voltage rises too slowly the converter does not get the
“kick” it needs to start switching properly. If the power supply
has a large capacitor, it may cause this problem. Remove the
capacitor and try again. The MMI does not require strict power
regulation.
2. Most electrical noise is present at start up when solenoids
and motor starters activate. This may also cause a momen-
tary brown out in power. To eliminate the effects of this on the
MMI, use a delay relay (3 seconds) on the DC line providing
power to the MMI. This will also prevent the problem of the
power supply capacitor as well.
Problems during
operation
Faulty operation of the MMI may be due to problems with
power quality. The MMI has been designed to work in environ-
ments where electrical noise is present. However, extreme
electrical noise will still cause problems. Make sure that the
system is properly earth grounded.
Sometimes communications fail. There are various reasons why this happens;
electrical noise, loose cables, time outs, and power loss. When communications
fail, the MMI tries to re-establish the communications link. During the time the MMI
is establishing communications, the keypad of the MMI will not respond. Function
key operations will be interrupted. The implication is that the MMI should not be
used for Emergency Stop applications. A loss of communications can happen at
any time. Using the function keys on the MMI for critical operations can lead to a
potential disaster. It is good programming practice to allow for safe operation in the
event of failure of the interface.
The use of proper grounding techniques will insure reliable communications. Make
sure the PLC and the MMI are connected to good earth ground sites. This allows
EMI (Electro-Magnetic Interference, commonly called electrical noise) to be
channeled to ground where it can no longer disrupt electrical operations. Be sure to
route communications cables in separate bundles and locations from AC power
and control wiring. Do not run communications cables near solenoid and relay coils
or AC and DC drive controllers. Care should also be taken to locate the MMI itself
away from sources of EMI.
4.2 Communications Problems
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