Rockwell-automation System Design for the Control of Electrical Noise Manual de usuario descargar pdf (Pagina 82)

Publication GMC-RM001A-EN-P — July 2001

9-6 High Speed Registration Inputs

Single Voltage Input (24V or 5V)

The figure below illustrates a typical registration filter circuit.

Figure 9.4

Registration filter circuit

• R1 lowers the circuit impedance which improves noise immunity.

It also ensures that the signal voltage falls rapidly when the

detector turns off. A lower R value is better, but is limited by the

drive capability of the detector and the dissipation in the resistor.

A 470 ohm resistor will dissipate 1.2W at 24V dc if on

continuously, hence it should be rated at 2W.

• The maximum value of R2 depends on the impedance of the

registration input (a volt drop to 10% of nominal is ideal). If input

impedance is less than 4.7k ohms, then R2 will require a lower

value (i.e., 10% of input impedance). If R2 is changed, use this

formula for the on-delay: Delay (uS) = R2 (ohm) x C (

F). A value

of 470 ohms should be acceptable for most cases.

• Capacitor C, together with R2, determines the on-delay. Capacitor

C, together with R1 + R2, determines the off-delay (as shown in

the table below).

k ohm

Delay

µs

Delay

Off

µs

Noise

Attenuation

factor

@ 1MHz

Noise

Attenuation

@1MHz

0.47 0.47 4.7 2 4 14 23

0.47 0.47 10 5 9 30 29

0.47 0.47 22 10 21 65 36

0.47 0.47 47 22 44 139 43

0.47 0.47 100 47 94 295 49

0.47 0.47 220 100 207 649 56

1 2 ... 77 78 79 80 81 82 83 84 85 86 87 ... 126 127

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Rockwell-automation System Design for the Control of Electrical Noise Manual de usuario Pagina 82