Wika T53 Uživatelský manuál stáhnout pdf (Strana 28)

3.0 Analogue Input Blocks

T53 has 2 Analogue Input Blocks to be configured individually. The constrcution of the

Blocks is in line with the standards from FOUNDATION Fieldbus and Profibus Nutzerorgani

sation respectively, and producer specific parameters have not been added. However, the

Analogue Input Blocks for Fieldbus Foundation and Profibus are dissimilar due to the para-

meter differences.

3.1 Analogue Input Blocks, Fieldbus Foundation

3.2 Overview

The AI block takes the manufacturer’s input data, selected by channel number, and makes it

available to other function blocks at its output.

3.3 Analogue Input Block Schematic

3.4 Description

Transducer scaling (XD_SCALE) is applied to the value from the channel to produce the

FIELD_VAL in percent. The XD_SCALE units code must match the channel units code (if one

exists), or the block will remain in O/S mode after being configured. A block alarm for units

mismatch will be generated. The OUT_SCALE is normally the same as the transducer, but

if L_TYPE is set to Indirect or Ind Sqr Root, OUT_SCALE determines the conversion from

FIELD_VAL to the output. PV and OUT always have identical scaling.

OUT_SCALE provides scaling for PV. The PV is always the value that the block will place in

OUT if the mode is Auto. If Man is allowed, someone may write a value to the output. The

status will prevent any attempt at closed loop control using the Man value, by setting the

Limit value to Constant.

The LOW_CUT parameter has a corresponding “Low cutoff” option in the IO_OPTS bit

string. If the option bit is true, any calculated output below the low cutoff value will be

changed to zero. This is only useful for zero-based measurement devices, such as flow. The

PV filter, whose time constant is PV_FTIME, is applied to the PV, and not the FIELD_VAL.

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Wika T53 Uživatelský manuál Strana 28