Omron NB3Q-TW**B series Connection Manual page 19

Precaution
Wiring
TIn the case of the NB Series, when grounding the positive terminal of power supply of 24
V to the NB, do not ground functional grounding terminal at NB side. Some functions of a
PC connected to the NB may cause a short circuit and the NB Unit may cause damage.
• Caution:
Depending on the types of PC, SG terminals of RS-232C port or USB port and contour of connector
can be connected. As the contour of tool port of the NB and the functional grounding terminal are not
insulated, they are connected. Therefore, connecting the PC allows GND terminal and functional
grounding terminal of the NB to be connected. If the power supply of 24V to the NB is grounded pos-
itively, grounding the functional grounding terminal allows a short circuit as shown in the diagram
below and may result in damage.
Power
Supply
Grounding Grounding
Test Function
The Test Function is performed on PC, and it has different behaviors with actual NB
running system. A problem may occur due to communication timing, cable differences and
unexpected PC circumstances (such as freeze). When the Test Function is performed,
please consider possible unexpected circumstances on the actual NB running system and
confirm that any dangerous event will not occur beforehand.
NB-series Programmable Terminals Host Connection Manual (V108)
NB
24V
GND
0V SG
Functional
Grounding
Contour Contour
Do not ground the functional grounding.
Caution
PC
Cable SG
Safety Precautions
15