NAVTELECOM SIGNAL S-2651 Operation Manual page 23

"Discrete NO +", "Discrete NC +", "Discrete NO-", "Discrete NC-" profiles must be specified in the settings.
"Discrete N3 -", "Discrete NO-" allow to operate with sensors which close the input to "ground" ("-" power)
when they are turned on or off.
Note:
With these profiles voltage is applied to the input through the built-in pull-up resistor Rpu. This allows not to
use an external "pull-up" resistor when operating with sensors which operates on "-" (by "ground").
Profiles "Discrete NC+" and "Discrete NO+" allow to work with sensors, which, when turned on or off, close
the input to "+" supply voltage.
R
1
Figure 28. Connection of normally open (NO-) sensors
R
pu
UIN
R
1
Figure 29. Connection of normally closed (NC-) sensors
VDD
R
pu
R
2
C
1
VDD
CPU_pull-up
CPU_adc
R
2
C
1
CPU_pull-up
CPU_adc