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5.4 Failsafe Limits
Another function of the ER3000 is to detect when programmable limits are
exceeded. Limits can be set on the following variables:
• Analog setpoint.
• Internal feedback.
• External feedback.
• Inner loop error signal.
• Outer loop error signal.
Associated with the limits is a failsafe state that is user defined to set the inlet
and exhaust valves in any desirable combination of open and/or closed states.
The default failsafe state is to close the inlet valve and open the exhaust valve so
that the system will be vented if a limit is exceeded.
Limits can be useful for providing added security in the event of a system failure
such as broken transducer wiring, lack of supply pressure, etc. When limits are
not desired the failsafe modes should be "disabled" (they are disabled when
shipped from the factory).
5.5 LEDs
There are four LEDs (light emitting diodes) on the boards to indicate the status
of the unit. The LEDs indicate the ER3000 is fundamentally operating correctly.
Refer to the Troubleshooting Section for more details on LED indicators.
5.6 RS485 Communication
RS485 communication provides a low cost yet efficient means of communicating
between a computer and a network of ER3000 controllers.
5.6.1 Protocol
In the network the computer serves as a master and all of the controllers as
slaves. Each controller must have a unique node number between 1 and 250.
Controllers have a default node number of 250 when shipped from the factory.
When configuring a network each controller must be individually powered up
and have a unique node number assigned, using Windows ER3000 (CVI) or
DOS tune.exe. The computer initiates all communication and the controllers
respond only to messages that are sent specifically to their node addresses.
The implementation of the Tescom protocol is explained fully in the Software
Programs Section of the manual.
5. Operation 31
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