Rockwell-automation 1769-IF4FXOF2F Compact Combination Fast Analog I/O Manual de usuario descargar pdf (Pagina 24)

24 Publication 1769-UM019A-EN-P - October 2008

Chapter 2 Installation and Wiring

For example, for Belden 8761 two conductor, shielded cable and a

1769-IF4 input module:

Rc = 52.5 Ω/1000 m

Rs = 1 Ω

Ri = 220 KΩ

As output impedance (Rs) and/or resistance (DC) of the cable (Rc) get

larger, system accuracy decreases. If you determine that the

inaccuracy error is significant, implementing the following equation in

the control program can compensate for the added inaccuracy error

due to the impedance of the module’s voltage outputs and cable.

Label the Terminals

A removable, write-on label is provided with the module. Remove the

label from the door, mark the identification of each terminal with

permanent ink, and slide the label back into the door. Your markings

(ID tag) will be visible when the module door is closed.

Effect of Output Impedance and Cable Length on Accuracy

Length of Cable DC Resistance of the Cable Rc Accuracy Impact at the

Input Module

50 m (164 ft) 2.625 Ω 0.00284%

100 m (328 ft) 5.25 Ω 0.00523%

200 m (656 ft) 10.50 Ω 0.01%

300 m (984 ft) 15.75 Ω 0.01477%

TIP

For current outputs, source and cable impedance do not impact

system accuracy as long as the total resistance of the cable and

input impedance of the load remain within the specified

maximum limits for the module's current outputs.

%Ai 1

Vin

---------

–

⎝⎠

⎛⎞

100×=

Vs Vin

Rs 2 Rc×()Ri++[]

--------------------------------------------------------

×=

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Rockwell-automation 1769-IF4FXOF2F Compact Combination Fast Analog I/O Manual de usuario Pagina 24