National Instruments NI 9234 - Manual (Page 28)

NI 9234 Operating Instructions and Specifications 28 ni.com
Safety
Safety Voltages
Connect only voltages that are within the following limits.
Channel-to-earth ground................... ±30 V max,
Measurement Category I
Isolation
Channel-to-channel .................... None
Channel-to-earth ground ............ None
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 the NI 9234 to signals or use for
measurements within Measurement Categories II, III,
or IV.