National Instruments RS485 - Manual (Page 15)

© National Instruments Corp. 15 NI 9871 Operating Instructions
Safety
Maximum Voltage 1
Connect only voltages that are within these limits.
RS485/RS422 Port-to-COM............. –8 to +13 VDC max,
Measurement Category I
V
SUP
-to-COM ................................... ±28 V max,
Measurement Category I
Measurement Category I is for measurements performed on
circuits not directly connected to the electrical distribution system
referred to as MAINS voltage. MAINS is a hazardous live electrical
supply system that powers equipment. This category is for
measurements of voltages from specially protected secondary
circuits. Such voltage measurements include signal levels, special
equipment, limited-energy parts of equipment, circuits powered by
regulated low-voltage sources, and electronics.
Caution Do not connect to signals or use for
measurements within Measurement Categories II, III,
or IV.
1 The maximum voltage that can be applied or output without creating a safety hazard.