NEC DTU-70 Instruction Manual page 57

(3) Control when a fault is encountered
a) Faults
A fault of a transmitter is classified into three (3) kinds as follows:
1) When this kind of fault is encountered, the operation of a transmitter is
stopped coercively. And the transmitter must be protected absolutely from
this kind of fault.
2) Even if this kind of fault is encountered, the transmitter can continue its
operation by switching the system automatically into the stand-by system.
The exciter section and the cooling section both adopting the stand-by
systems are controlled.∗
∗ Stand-by systems are only P type TX
3) If this kind of fault is encountered, the transmitter is not stopped coercively,
however, the signals informing a fault must be sent to the external circuit.
When a fault is encountered at a transmitter, the sensor detects the fault and
transmits the response to the TX control. Then, the TX control decides the
kind in which the fault is encountered, thus, controlling the transmitter.
• Faults from which the transmitter must be protected;
The following faults, if encountered require the transmitter to be protected.
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