ADIS16228SLASHPCBZ datasheet(15/28 Pages) AD

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Data Sheet

ADIS16228

Rev. B | Page 15 of 28

Dynamic Range Settings

REC_CTRL2 (see Table 14) provides four range settings that

are associated with each sample rate option, SRx. The range options

that are referenced in REC_CTRL2 reflect the maximum dynamic

range, which occurs at the lower part of the frequency range and

does not account for the decrease in range (see Figure 16). For

example, set REC_CTRL2[5:4] = 10 (DIN = 0x9C20) to set the

peak acceleration (AMAX) to 10 g on the SR2 sample rate option.

These settings help optimize FFT precision and sensitivity when

monitoring lower magnitude vibrations. For each range setting

in Table 14, this stage scales the time domain data so that the

maximum value equates to 215 LSBs for time domain data and

216 LSBs for frequency domain data.

Note that the maximum range for each setting is 1 LSB smaller

than the listed maximum. For example, the maximum number

of codes in the frequency domain analysis is 216 − 1, or 65,535.

For example, when using a range setting of 1 g in one of the FFT

modes, the maximum measurement is equal to 1 g times 216 − 1,

divided by 216. See Table 15 for the resolution associated with

each setting and Figure 14 for the location of this operation in

the signal flow diagram. The real-time mode automatically uses

the 20 g range setting.

Table 14. REC_CTRL2 (Base Address = 0x1C), Read/Write

Bits

Description (Default = 0x00FF)

[15:8]

Not used (don’t care)

[7:6]

Measurement range, SR3

00 = 1 g, 01 = 5 g, 10 = 10 g, 11 = 20 g

[5:4]

Measurement range, SR2

00 = 1 g, 01 = 5 g, 10 = 10 g, 11 = 20 g

[3:2]

Measurement range, SR1

00 = 1 g, 01 = 5 g, 10 = 10 g, 11 = 20 g

[1:0]

Measurement range, SR0

00 = 1 g, 01 = 5 g, 10 = 10 g, 11 = 20 g

Table 15. Range Settings and LSB Weights

Range Setting (g)

(REC_CTRL2[5:4])

Time Mode

(mg/LSB)

FFT Mode

(mg/LSB)

0 to 1

0.0305

0.0153

0 to 5

0.1526

0.0763

0 to 10

0.3052

0.1526

0 to 20

0.6104

0.3052

Scale Adjustment

The x_SENS registers (see Table 16, Table 17, and Table 18)

provide a fine-scale adjustment function for each axis. The

following equation describes how to use measured and ideal

values to calculate the scale factor for each register in LSBs:

SCFx =









− 1

× 218

where:

is the ideal x-axis value.

is the actual x-axis measurement.

These registers contain correction factors, which come from the

factory calibration process. The calibration process records

accelerometer output in four different orientations and

computes the correction factors for each register.

These registers also provide write access for in-system adjust-

ment. Gravity provides a common stimulus for this type of

correction process. Use both +1 g and −1 g orientations to reduce

the effect of offset on this measurement. In this case, the ideal

measurement is 2 g, and the measured value is the difference of

the accelerometer measurements at +1 g and −1 g orientations.

The factory-programmed values are stored in flash memory and

are restored by setting GLOB_CMD[3] = 1 (DIN = 0xBE04)

(see Table 64).

Table 16. X_SENS (Base Address = 0x02), Read/Write

Bits

Description (Default = N/A)

[15:0]

X-axis scale correction factor (SCFx), twos complement

Table 17. Y_SENS (Base Address = 0x04), Read/Write

Bits

Description (Default = N/A)

[15:0]

Y-axis scale correction factor (SCFy), twos complement

Table 18. Z_SENS (Base Address = 0x06), Read/Write

Bits

Description (Default = N/A)

[15:0]

Z-axis scale correction factor (SCFz), twos complement

PRE-FFT WINDOWING

REC_CTRL1[13:12] provide three options for pre-FFT windowing

of time data. For example, set REC_CTRL1[13:12] = 01 to use

the Hanning window, which offers the best amplitude resolution

of the peaks between frequency bins and minimal broadening

of peak amplitudes. The rectangular and flat top windows are

also available because they are common windowing options for

vibration monitoring. The flat top window provides accurate

amplitude resolution with a trade-off of broadening the peak

amplitudes.

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