GE b30, Instruction Manual

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CHAPTER 3: INSTALLATION WIRING
B30 BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 3-27
3
Figure 3-24: Contact input connected to a contact output with resistor (R2) across the input
Application example
This example is for illustrative purposes only and the calculations present the worst-case scenario. In practice, the value of
debounce time can be lower.
Contact input ON state impedance used in the calculation of the discharge period is based on the following table.
Table 3-4: Discharge period
Debounce time setting = 2 ms
Assume a stray capacitance of 0.1
μ F.
Assume an initial voltage across the stray capacitance "Vinitial" = 19 V (Vthreshold - 65 V), where Vthreshold = 84 V. The
initial voltage Vinitial depends on values of impedance of R1 and contact inputs when the contact input is OFF (non-
activated state).
Therefore, discharge time constant (
τ ) =50 k Ω *0.1 μ F = 5 ms.
Discharge period t is calculated from the following equation:
Vthreshold = (Vbatt - VInitial) *e^ (-t/ τ )
84 = -149 *e^ (t/0.005) Eq. 3-1
T = -0.005 * ln (84/149) = 0.0029 s
Therefore, in this example the contact inputs operate.
To prevent this operation, the debounce time must be increased to 4 ms (set debounce time as per the following table) or
insert a resistor less than or equal to "R" as calculated later.
Table 3-5: Typical debounce time setting
Battery voltage (V) Input impedance (k
Ω
)
130 50
250 97
Stray capacitance ( μ F) Battery voltage (V) Debounce time (ms)
0.05 130 2
0.1 130 4
0.2 130 6
0.05 250 3