IC-GD datasheet(29/55 Pages) ICHAUS

29 / 55 page

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iC-GD

UNIVERSAL I/O INTERFACE

Rev A1, Page 29/55

read back via the SPI (Xmeas). The two maximum val-

ues are used for all measuring ranges (value 1 and 2).

In addition, for the symmetric measuring ranges, the off-

set at 0 V/0 mA (value 0) is determined. For the current

measurement offset, also the current chip temperature

and the temperature coefficient values AITKQ, AITKL

are required. The latter are stored on the chip, see table

17. The required values are used unitless in the format

of the process data: Xset und Xmeas as signed numbers,

and additionally for the current measurement AITKQ,

AITKL and CHIP_TEMP, all as unsigned numbers.

The following four conditions must be kept:

1.5 +

AGFnx

215

∗

AOFnx + 215 > 215 − 1

1.5 +

AGFnx

215

∗

AOFnx − 215 < −215

1.5 +

AGFnx

215

∗

AOFnx < 215 − 1

1.5 +

AGFnx

215

∗

AOFnx > −215

3-point calibration (symmetrical ranges)

The following formulae are valid for the ranges ±10 V,

±1 V, ±100 mV, ±10 mV, ±20 mA.

Point 0 is calibrated exactly (to use for offset), point 1

and point 2 are calibrated best possible. The points

should be distributed equidistantly.

Example

Point 0: 0 V, point 1: +10 V, point 2: -10 V.

AGFnx =

Xset 1 − Xset 0

Xmeas 1 − Xmeas 0

Xset 2 − Xset 0

Xmeas 2 − Xmeas 0

−

3 ∗ 214

AOFnx(VI) =

Xset 0

1.5 + AGFnx

215

−

Xmeas 0

AOFnx(CI) =

Xset 0

1.5 + AGFnx

215

−

Xmeas 0 ∗

f T

2-point calibration (asymmetrical ranges)

The following formulae are valid for the ranges -17.5 mV

to 87.5 mV, -4.375 mV to 21.875 mV, 4 to 20 mA. Point

1 and point 2 are to be adjusted exactly.

Example

Point 1: 4 mA, point 2: 20 mA.

AGFnx =

Xset 2 − Xset 1

Xmeas 2 − Xmeas 1

−

1.5 ∗ 215

AOFnx(VI) =

Xset 1 ∗ Xmeas 2 − Xset 2 ∗ Xmeas 1

Xset 2 − Xset 1

AOFnx(CI) =

Xset 1 ∗ Xmeas 2 − Xset 2 ∗ Xmeas 1 + c0 ∗ (f T − 1) ∗ (Xset 2 − Xset 1 + Xmeas 1 − Xmeas 2)

(Xset 2 − Xset 1) ∗ f T

with

c0 = 7710,

f T = 1 +

AITKL ∗ CHIP_TEMP

218

−

AITKQ ∗ CHIP_TEMP2

222

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