Rockwell-automation 1769-IF4XOF2 Compact 8-Bit Low Resolution Analog I Manual do Utilizador descarregar pdf (Página 34)

Publication 1769-UM008A-EN-P - November 2001

3-12 Installation and Wiring

For example, for Belden 8761 two conductor, shielded cable:

Rc = 16

Ω/1000 ft

Rs = 0 (ideal source)

As input source 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 source and cable.

Table 3.1 Effect of Cable Length on Input Accuracy

Length of Cable (m) dc resistance of the

cable, Rc (Ω

ΩΩ

Ω)

Accuracy impact at the

input module

50 2.625 0.00350%

100 5.25 0.00700%

200 10.50 0.01400%

300 15.75 0.02100%

TIP

In a current loop system, source and cable

impedance do not impact system accuracy.

Vin

---------

–





100×=

Vs Vin

×()

++[]

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

×=

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Rockwell-automation 1769-IF4XOF2 Compact 8-Bit Low Resolution Analog I Manual do Utilizador Página 34