Maintenance
82 Rev. D7 Jul 2017 Marathon MM
11.2 Fail-Safe Operation
The Fail-Safe system is designed to alert the operator and provide a safe output in case of any system
failure. Basically, it is designed to shutdown the process in the event of a set-up error, system error, or
a failure in the sensor electronics.
The Fail-Safe circuit should never be relied on exclusively to protect critical heating
processes. Other safety devices should also be used to supplement this function!
When an error or failure does occur, the display indicates the possible failure area, and the output
circuits automatically adjust to their lowest or highest preset level. The following table shows the values
displayed on the control panel and transmitted over the serial interface.
Internal temperature over range
Internal temperature under range
Target temperature under range
Target temperature over range
Table 12: Error Codes and Current Output Values
The relay is controlled by the temperature selected on the display. If any failsafe code appears on the
display, the relay changes to the “abnormal” state. This causes the relay to change state, leaving a
normal numerical temperature output.
If two errors occur simultaneously, the higher priority error is the one that is presented on the digital
and analog outputs. For example, if the internal temperature is too high and the target temperature is
over range, the unit outputs EIHH on the display and digital output and 21 mA on the analog output.
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