The central control system shows LO TRA
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LO TRA occurred in Zhejiang University’s control system
Measure the current value of this channel; it should be less than 4mA.
If the current is less than 4MA, it is usually due to a broken wire; if it is even lower than 4MA, an ERR message will be displayed
TRA stands for broken connection, no signal received； ERR means less than 4mA, or greater than 20mA