Rockwell-automation 1746-NR4 SLC RTD/Resistance Input Module User Manu Manual de usuario descargar pdf (Pagina 47)

Publication 1746-UM008B-EN-P - December 2006

Install and Wire the Module 47

Calibration

The accuracy of a system that uses the RTD module is determined by:

• the accuracy of the RTD.

• resistance mismatch of the cable wires that connect the RTD to

the module.

• the accuracy of the RTD module.

For optimal performance at the customer site, the RTD module is

calibrated at the factory prior to shipment. In addition, a

self-calibration feature, called autocalibration, further ensures that the

module performs to specification over the life of the product.

Factory Calibration

The four-pin calibration connector, on the RTD module circuit board,

is used for factory setup only.

Auto-calibration

When a channel becomes enabled, the module configures the channel

and performs an auto-calibration on the channel. The channel is

selected, the excitation current is turned off, and the three input lines

for the channel are connected to analog common. The module’s A/D

converters are configured for the proper gain and filter frequency that

is appropriate for your RTD configuration. Auto-calibration performs

an A/D conversion on the zero voltage (analog common) and the

full-scale voltage (A/D reference voltage) on the following signals:

• Lead wire signal

• RTD/resistance signal

• Excitation current signal

These conversions generate offset (zero reference) and full scale (span

reference) coefficients that are saved and used by the module to

perform future A/D conversions on this channel.

IMPORTANT

Channel calibration time is shown in the Channel Calibration

Time table.

1 2 ... 42 43 44 45 46 47 48 49 50 51 52 ... 147 148

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Rockwell-automation 1746-NR4 SLC RTD/Resistance Input Module User Manu Manual de usuario Pagina 47