Automation Direct DL205 Manual page 36

3–12
I/O Wiring and Specifications
PLC Relay Output
DL205 Installation and I/O Manual, Rev. B
Output
R
C
Common
The RC network must be located close to the relay module output connector. To find
the values for the RC snubber network, first determine the voltage across the
contacts when open, and the current through them when closed. If the load supply is
AC, then convert the current and voltage values to peak values:
Now you are ready to calculate values for R and C, according to the formulas:
2
I
C (mF) =
10
C minimum = 0.001 mF, the voltage rating of C must be w V, non-polarized
R minimum = 0.5 W, 1/2 W, tolerance is " 5%
For example, suppose a relay contact drives a load at 120VAC, 1/2 A. Since this
example has an AC power source, first calculate the peak values:
I = I x 1.414, = 0.5 x 1.414 = 0.707 Amperes
peak rms
V = V
peak rms
Now, finding the values of R and C,:
2
I
C (mF) = =
10
V
R (W) = , where x=
x
10 x I
50
x= 1 + = 1.29
169.7
Supply
+ –
V
R (W) =
10 x I
x 1.414 = 120 x 1.414 = 169.7 Volts
2
0.707
= 0.05 mF, voltage rating w 170 Volts
10
50
1 +
V
169.7
R (W) =
10 x 0.707
Inductive Field Device
Input
Common
50
, where x= 1 +
x
V
= 26 W, 1/2 W, " 5%
1.29