This standard specifies the analog direct current signals used to transmit information between system components in industrial process measurement and control systems. This section does not apply to signals used entirely within a component.
GB/T 3369.1-2008 history
2008GB/T 3369.1-2008 Analogue singals for process control systems.Part 1:Direct current signals
1989GB/T 3369-1989 Analogue direct current signals for industrial process measurement and control instruments