CNC4PC C10 - Calculating NPN Sensor Resistor Value

User’s Manual Page 9
Some NPN proximity sensors have an internal pull-up resistor (R1). It is necessary to
know its value in order to safety connect the sensor with the BOB. Follow this
recommendation:
Connecting NPN open collector proximity sensor with the C25
(R1+R2) Value (12V)
(R1+R2) Value (24V)
Approx. 10KΩ
Approx. 25KΩ
CALCULATING THE R1 VALUE
Note: Rx is the unknown resistor value.
Where:
V
EX
is the external power supply voltage
V is the voltage across the R resistor
R
X
= V
EX
.(R/V) - R (1)
A voltmeter is required to calculate the internal resistor value (Rx). Do the connections
as are shown in the figure above and do the calculations using the equation (1).
Note. R value has to be known to do this operation. A 4.7KOhm@1/2W is
recommended.