Rockwell-automation 1769-IF4FXOF2F Compact Combination Fast Analog I/O Instrukcja Użytkownika Pobierz pdf (Strona 22)

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

Chapter 2 Installation and Wiring

Effect of Transducer/Sensor and Cable Length Impedance on

Voltage Input and Output Accuracy

For voltage inputs and outputs, the length of the cable used between

the transducer/sensor/load and the module can affect the accuracy of

the data provided by the module.

Voltage Input Accuracy

Where:

Rc = DC resistance of the cable (each conductor) depending on

cable length

Rs = Source impedance of analog transducer/sensor input

Ri = Impedance of the voltage input (220 kΩ)

Vs = Voltage source (voltage at the transducer/sensor input device)

Vin = Measured potential at the module input

%Ai = Percent added inaccuracy in a voltage-based system due

to source and cable impedance

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

Rc = 5.25 Ω/1000 m

Rs = 0 (ideal source)

V in

RcRs

Effect of Cable Length on Input Accuracy

Length of Cable,

m (ft)

DC Resistance of the Cable,

Rc (Ω)

Accuracy Impact at the

Input Module

50 (164) 2.625 0.002385%

100 (328) 5.25 0.00477%

200 (656) 10.50 0.00954%

300 (984) 15.75 0.01431%

Vin

Ri Vs×[]

Rs 2 Rc×()Ri++

[]

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

%Ai 1

Vin

---------

–

⎝⎠

⎛⎞

100×=

1 2 ... 17 18 19 20 21 22 23 24 25 26 27 ... 93 94

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