Gain Factor Calculation; Temperature Measurement - Analog Devices EVAL-AD5933EBZ User Manual

Evaluation Board User Guide

GAIN FACTOR CALCULATION

The code shown in the Evaluation Board Source Code Extract
section for the impedance sweep is based on a single point gain
factor calculation. This calculation is carried out once system
calibration is at the midpoint sweep frequency and with a
known impedance connected between VOUT and VIN. The
gain factor is calculated by exciting the calibration impedance with
a 2 V p-p sinusoid with a frequency of 30.750 kHz. The PGA
setting is ×1. The calibration is carried out with a 100 kΩ
resistor connected between VOUT and VIN. The feedback
resistor is 100 kΩ. The magnitude of the real and imaginary
component at the calibration frequency is given by the formula
2 2
= +
Magnitude R I
where:
R is the real component.
I is the imaginary component of the calibration code.
Example Code for Temperature Measurement
Private Sub MeasureTemperature()
' The Digital temperature Result is stored over two registers as a 14 bit twos complement number.
' 92H <D15-D8> and 93H<D7 to D0>.
Dim TemperatureUpper As Long.
Dim TemperatureLower As Long
'Write xH90 to the control register to take temperature reading.
WritetToPart &H80, &H90
msDelay 5 'nominal delay
ReadbackStatusRegister = PortRead(&HD, &H8F)
ReadbackStatusRegister = ReadbackStatusRegister And &H1
'if a valid temperature conversion is complete, ignore this.
If ReadbackStatusRegister <> 1 Then
'loop to wait for temperature measurement to complete.
Do
ReadbackStatusRegister = PortRead(&HD, &H8F)
ReadbackStatusRegister = ReadbackStatusRegister And &H1
Loop Until (ReadbackStatusRegister = 1)
Form1.Label10.Caption = "Current Device Temperature"
MsgBox "Device Temperature Measurement Complete"
End If
' The Digital temperature Result is stored over two registers as a 14 bit twos complement number.
' 92H <D15-D8> and 93H<D7 to D0>.
TemperatureUpper = PortRead(&HD, &H92)
TemperatureLower = PortRead(&HD, &H93)
Temperature = TemperatureLower + (TemperatureUpper * 256)
If Temperature <= &H1FFF Then ' msb =0.
' Positive Temperature.
Label8.Caption = (Temperature / 32#)
Else
' Negative Temperature.
The gain factor is then given by
GainFactor
Refer to the AD5933

TEMPERATURE MEASUREMENT

Refer to the AD5933
sensor. The temperature sensor data is stored in a 14-bit twos
complement format. The conversion formula is given in the
AD5933 data sheet.
Rev. 0 | Page 17 of 28
⎛ ⎞
1
⎜ ⎜ ⎟ ⎟
⎛ ⎞
⎝ Impedance ⎠
Admittance
= =
⎜ ⎟
⎝ ⎠
Code Magnitude
data sheet for more details.
data sheet for details on the temperature
UG-364
⎛ ⎞
1
⎜ ⎟
⎜ ⎟
100 kΩ
⎠
⎝
=
Magnitude