Texas Instruments PGA309 Quick Start Manual

PGA309

Quick Start System Reference

Guide

by Art Kay

High-Precision Linear Products

SBOA103C
Jan 2006

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System Reference Guide

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PGA309 Quick Start

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System Reference Guide

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Required Equipment……………………………………………………..………4
Definition of sensor specifications………………………………………………5-12
PGA309 Absolute Calibration Example..……….………………………………13

Step 1: Will the PGA309 work for your application?..…..………………14-17
Step 2: Set up hardware……………………………………………..…..…18-21
Step 3: Configure PGA309 for initial scaling.……………………………..22-31
Step 4: Configure Sensor-Emulator-EVM to emulate

sensor……………………………………………………...………….…..…32-38

Step 5: Use the Calibration Spreadsheet to perform the calibration …39-59
PGA309 Ratiometric Calibration Example…………………………………..…60-86
PGA309 With Output Scaling Example………………………………………...87-95
PGA309 In Three-Wire Mode …………………………………………………..96-100

PGA309 Quick Start Contents

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Required items for Quick Start

Hardware

• PGA309EVM –This is an evaluation kit that allows you to communicate with and interface to the PGA309. It
contains a PC Interface Board and a Sensor Interface Board combined with a PGA309 and EEPROM.

• Sensor-Emulator-EVM –This is an evaluation kit that uses rotary switches and trim potentiometers to
generate voltage excited bridge sensor output signals and temperature sensor output signals.

• +/-12V supply – Any low noise dc supply for the sensor emulator.

• Precision DVM – Any five or six digit meter that can read into microvolts(e.g., HP3458, HP34401).

• Slotted Jeweler’s Screwdriver –The best tool to quickly adjust the potentiometer.

Software

• PGA309DK Board Interface –This software is used to communicate with the PGA309EVM. See

http://focus.ti.com/docs/toolsw/folders/print/pga309evm-eu.html under support software for free download.

• PGA309 Calculator –This software is used to do initial gain scaling and verify that the design does not violate any

PGA309 specifications. Software is bundled with PGA309DK Board Interface software.

• PGA309 Calibration Spreadsheet – This spreadsheet uses PGA309 / Sensor readings over temperature and at

different applied stimulus levels to generate the calibration table used to correct for the sensor errors. Software is
bundled with PGA309DK Board Interface software.

• Generate_Emulator_Values.xls –This spreadsheet translates sensor specifications into voltage settings for the

Sensor-Emulator-EVM. See http://focus.ti.com/docs/toolsw/folders/print/sensor-emulator-evm.html under support
software for free download.

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Specifications

There are several key specifications that are used throughout our literature.

The mathematical definitions are listed below.

• Offset – the normalized output of a sensor (in V/V) with no applied stimulus.

• OffsetTC1 –The linear drift of the sensors’offset given in % of span/oC.

• NonlinOffsetDrift –The second order (quadratic) drift of the offset. This
coefficient is in % of span at room temperature.

• OffsetTC2 –The second order (quadratic) drift of the offset. This
coefficient is in % of span/oC2at room temperature.

• Span – the amount of change in normalized output voltage (in V/V) of the
sensor over the entire range of applied stimulus.

• SpanTC1 –The linear drift of the sensors’span given in % of span/oC.

• NonlinSpanDrift –The second order (quadratic) drift of the offset. This
coefficient is in % of span at room temperature.

• SpanTC2 –The second order (quadratic) drift of the span. This coefficient
is in % of span/oC2at room temperature.

• PressureNonlinearity–The second order (quadratic) nonlinearity versus
applied signal given in % of span.

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Span –the amount of change in normalized output voltage (in V/V) of the
sensor over the entire range of applied stimulus.

Offset –the normalized output of a sensor (in V/V) with no applied
stimulus.

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OffsetTC1

Offset3Offset

1

−

(

)

Span2T3T1−

( )

⋅

OffsetTC1

2.963 10

6−

× 1.624− 10

4−

×

( )

−





3.673 10

3−

× 85 40−( )−[ ]⋅

3.602 10

4−

×

% of span/oC

Bridge Sensitivity vs Temp

-5.0E-04

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

3.5E-03

4.0E-03

-50 0 50 100 150

Temp, degC

Kbridge, V/V

offset
span

(T2, Span2)

(22.5C, 3.67E-3)

(T3, Offset3)

(85C, 2.96E-6)

(T2, Offset2)

(22.5C, 1.02E-3)

(T1, Offset1)

(-40C, -1.62E-3)

Linear end point fit is used to
determine the linear drift.

The linear drift of the
sensor’s offset given in
% of span/oC.

OffsetTC1

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NonLinOffsetDrift

Offset

2

Offset1Offset

3

+

(

)

2

−







Span

2

NonLinOffsetDrift

1.023104−⋅

1.624− 104−⋅

( )

2.963106−⋅

( )

+





2

−

3.673 103−×

4.956 102−×

% of span

OffsetTC2

NonLinOffsetDrift

T3T1−

( )

2







2

4.956 102−×

85 40−( )−[ ]

2







2

1.269 105−×

% of span/oC

2

Bridge Sensitivity vs Temp

-5.0E-04

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

3.5E-03

4.0E-03

-50 0 50 100 150

Temp, degC

Kbridge, V/V

offset
span

OffsetTC2:

The second order (quadratic) drift of
the offset. This coefficient is in %of

span/oC2at room temperature.

NonlinOffsetDrift:

The second order (quadratic) drift
of the offset. This coefficient is in

% of span at room temperature.

NonlinOffsetDrift
OffsetTC2

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Bridge Sensitivity vs Temp

-5.0E-04

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

3.5E-03

4.0E-03

-50 0 50 100 150

Temp, degC

Kbridge, V/V

offset
span

SpanTC1

Span3Span

1

−

(

)

Span2T3T1−

( )

⋅

SpanTC1

3.7284103−⋅ 3.4412103−⋅−

( )

3.6734 10

3−

× 85 40−( )−[ ]⋅

6.255 10

4−

×

% of span/oC

The linear drift of the
sensors’span given
in % of span/oC.

SpanTC1

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NonLinSpanDrift

Span

2

Span1Span

3

+

( )

2

−







Span

2

NonLinSpanDrift

3.6734 103−×

3.4412103−⋅

( )

3.7284103−⋅

( )

+





2

−

3.6734 103−×

2.412 102−×

% of span

SpanTC2

NonLinSpanDrift

T3T1−

( )

2





2

2.412 102−×

85 40−( )−[ ]

2







2

6.175 106−×

% of span/oC

2

Bridge Sensitivity vs Temp

-5.0E-04

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

3.5E-03

4.0E-03

-50 0 50 100 150

Temp, degC

Kbridge, V/V

offset
span

(T3, Span3)

(85C, 3.73E-3)

(T1, Span1)

(-40C, 3.44E-3)

(T2, Span2)

(22.5C, 3.67E-3)

The nonlinear coefficient assumes T2 is
equal distant t o T1 and T3. Thus the
vertex of the parabola will be at T2.

NonlinSpanDrift:

The second order (quadratic) drift of
the offset. This coefficient is in % of

span at room temperature.

NonlinSpanDrift
SpanTC2

SpanTC2:

The second order (quadratic) drift of
the span. This coefficient is in % of

span/oC2at room temperature.

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Sensor Output vs Applied Stimulus

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

3.00E-03

3.50E-03

4.00E-03

0 10 20 30 40 50 60 70 80 90 100 110

Applied Stimulus (%)

Sensor output (V/V)

ideal span
span

slope

real_sensor

100

real_sensor

0

−

(

)

stim

100

stim0−

( )

3.67103−⋅ 0−

(

)

100 0−( )

3.67 105−×

ideal_sensor stim( ) slopestim⋅

ideal_sensor 50( ) 3.67 105−×

( )

50⋅ 1.835 103−×

PresureNonlinearity

real_sensor50ideal_sensor

50

−

( )

real_sensor

100

100⋅

1.66 103−× 1.835 103−×−

( )

3.67 103−×

( )

100⋅ 4.768− %

The second order (quadratic)
nonlinearity versus applied signal
given in % of span.

Note: These readings were all
taken at room temperature. So,
real_sensor100 is the span of the
sensor at room temperature.

Pressure
Nonlinearity

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P

nonlin

P() P 4Nonlinearity_pct⋅ 100⋅

P

100P100





2

−













⋅+

Span_TCT() SpanTC1T T

room

−

( )

⋅ SpanTC2T T

room

−

( )

2

⋅−

Offset_TCT() OffsetTC1T T

room

−

( )

⋅ OffsetTC2T T

room

−

( )

2

⋅−

SensorOutputPT,( ) Offset

room

Span

room

Offset_TCT()⋅+ Span

Nonlinearity_pct

100

1 Span_TCT()+( )⋅







⋅+







The equations use the constants defined on the previous slides. These
equations are used in the generate_emu_settings.xls spreadsheet* to
compute the voltage settings for the Sensor-Emulator-EVM.

Sensor Output Equations

* Available for download at www.ti.com as SBOC065

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For this quick start example the specifications below and the example hardware configuration will be used.
The Sensor-Emulator-EVM will create an equivalent for the illustrated Real World Inputs.

“generate_sim_values.xls
“Offset and Span”Tab

PGA309 Absolute
Calibration Example

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Step 1: Will the PGA309
work for my sensor?

•Use your sensor’s specifications with the PGA309
Calculator software tool (SLVC073) to see if the PGA309
has the gain and offset adjustment range required to
accommodate your sensor.

•Use the PGA309 Calculator software tool to verify that
your design does not violate any of the most critical
PGA309 specifications (internal or external nodes).

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Enter
information
here. For
example,
enter the
values shown.

Press Compute
Constants and
the resulting gain
settings will be
displayed here.

Enter your sensor parameters and your PGA309
configuration parameters to get the gain scaling.

If your design
generates values
for gain and offset
that are out of the
PGA309’s range,
the software will
flag the problem.

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The program selects values to allow
the Gain DAC and Zero DAC to have
the maximum adjustable range. The
Set Additional Constraints button is a
way to force the front end gain or
coarse offset to a constant. For this
example, set the coarse offset zero to
minimize noise. Click Apply

Constraints and then click Compute
Constants. In this case the range of

adjustment for the Zero DAC is
reduced but is still adequate to
correct for the sensor drift.

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After the gains and offsets of the
PGA309 have been calculated, press
Simulate Device to see if any internal
nodes are out of range.

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Step 2: Connect the hardware

Example of a Typical Engineering Bench Setup Using the Sensor Emulator

This diagram illustrates an example of how the Sensor-Emulator-EVM would be used in an engineering bench
setup. The PGA309 is a programmable sensor signal conditioning chip. The Sensor-Emulator-EVM can be used
in conjunction with the PGA309EVM (both versions) to facilitate the development of the PGA309 application.

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Jumper setup of PGA309EVM-xx and connections
to PC, power, and the Sensor-Emulator-EVM

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Required Electrical Connections to
Sensor-Emulator-EVM

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These jumpers
must be set to the
position shown to
allow the on-board
voltage reference
to generate the
emulated diode
voltages.

Sensor-Emulator-EVM Jumper Setup

These three
channels are used
to set the
temperature output
signal in the diode
mode. The Rt
channels are not
used in this mode.

Set the jumper
JUMP1 to the
position shown to
connect the
Diode
temperature
emulation.

Set the jumper
JUMP5 to the
position shown
to connect GND
to the bottom of
the bridge
emulator.

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Step 3: Do initial setup of the
PGA309 using the PGA309 DK
Program

•Copy the PGA309 Calculator results into the
PGA309DK software.

•Configure the PGA309 Temp ADC

•Calibrate the ADS1100 (ADC on PGA309EVM-xx
PC Interface Board Used to read the PGA309
output; read via software).

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Start the PGA309 Designer’s Kit
Control Program. When it starts,
a message box will ask if you want
to load from the EEPROM (Press
No). Another box will indicate that

“the PGA309 EVM was detected
using the One-Wire interface.”

If the PGA309EVM does not work
properly, refer to the PGA309EVM
Users Guide.

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For this example, we will measure the PGA309 output voltage using an delta-sigma A/D converter on
the PGA309 PC Interface Board (the ADS1100). For optimal accuracy the ADS1100 should be
calibrated. To calibrate the ADS1100, measure the supply voltage Vs on the PGA309 PC Interface
Board (this should be close to 5V).

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Press the Board
Settings button to
enter the calibration
factors. Enter the
measured value for
Vs then click
Read ADS1100.

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For the next part of the ADS1100
calibration, the input of the ADS1100
is shorted. The two boards must be
separated so that the PGA309 output
is not shorted by the calibration.

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Press calibrate
ADS1100. This will short
the input to the ADS1100
and measure the offset.
The calibration will take a
few seconds. When it is
complete close the
window.

When this step is done,
plug the two PGA309EVM
boards back together. At

this point the calibration
is complete.

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Step B:

Make sure PGA309 Test Pin HIGH
is checked. During calibration, the
PGA309 test pin must be set high.
This pin prevents the PGA309 from
reading the EEPROM during
calibration.

Step A:

It is a good practice to
press reset at the
beginning of a calibration
to insure all the registers
are in a known state.

Initial Configuration for the PGA309

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Set the reference and
bridge excitation
voltage to the proper
values used in the
PGA309 Calculator.

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Copy the gain and
offset settings from the
PGA309 Calculator to
the PGA309
Designer’s Kit Control
Program.

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Step A:

Configure the
temperature ADC by
pressing the ADC
Config button. The
example settings
shown are good for a
diode measurement.

Step B:

Enter the example
settings shown for a
diode temperature
measurement. Press
OK when done.

Step C:

Press Write PGA309 to copy
all the information entered in
the program into the registers
of the PGA309.

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Step 4: Configure
Sensor-Emulator-EVM to
Emulate the Bridge Sensor

1. In order to use the Sensor-Emulator-EVM, you have to adjust a
number of trim potentiometers to configure the Sensor-Emulator­EVM so that it acts like your sensor. If the sensor’s raw output
characteristics are known, this step is simple: you adjust the Sensor­Emulator-EVM output to mimic your sensor.

2. In the case where you want to use a sensor data sheet to configure
the Sensor-Emulator-EVM, you can use the
generate_emu_settings.xls to translate your specifications to
Sensor-Emulator-EVM settings. Unfortunately, sensor manufacturers
may have specifications that do not conform to a standard, and
sometimes the specifications are difficult to understand. For our
tools we will mathematically define the specifications. You mayhave
to translate your particular specifications to our format.

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1. Offset and Span: Generates the bridge output voltages.

2. Diode Vo: Generates the temperature sensor output voltages for the diode method.

3. Rt-: Generates the temperature sensor voltages for the Rt-method.

4. Rt+: Generates the temperature sensor voltages for the Rt-method.

5. PGA309 Error: Allows you to read the PGA309 via the ADS1100 (The ADS1100 is the
delta-sigma A/D converter that is a part of the PGA309EVM-xx).

6. PGA309 RatioMetricError: Allows you to read and compute error for a ratiometric PGA309
setup.

If the raw output of the sensor is not known, the “Generate_Sim_Values.xls”spreadsheet can be used to
translate the specifications of your bridge sensor and temperature sensor to system voltage levels. The
spreadsheet contains five sections (Offset and Span, Diode Vo, Rt-, Rt+, PGA309 Error, Ratiometric Error):

The temperature measurement methods, Diode, Rt-, and Rt+ are described in detail in the Sensor­Emulator-EVM System Reference Guide (SBOA102) and the PGA309 Users Guide (SBOU024).

Configuring the Emulator to
Emulate a Real World Sensor

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All the areas shown in light blue are either sensor specifications or system requirements. Enter these values and the
spreadsheet will generate output voltage settings for each channel on the sensor emulator. The next several pages will
show how the voltages listed in the spreadsheet are used to program the Sensor-Emulator-EVM.

Enter these
for our
example

Set Sensor-Emulator-EVM
potentiometers to generate these
voltages as detailed in pages 35-36

Generates the bridge output voltages from sensor specifications (“Generate_Sim_Values.xls”)

Offset and Span:

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Bridge Sensitivity vs Temp

-1.0E-03

-5.0E-04

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

3.5E-03

4.0E-03

4.5E-03

-50 0 50 100 150

Temp, degC

Kbr idge, V/V

offset
span

Each channel on the top section of the sensor emulator
represents a applied stimulus and temperature combination for
the sensor. Adjust the potentiometers coarse first, then fine, to
match the values computed by the Generate_Sim_Values.xls
spreadsheet for cold (0%. 50%, 100%), room (0%, 25%, 50%,
75%, 100%), and hot (0%, 50%, 100%). For example, the
sensor output at cold temperature and 0% of applied stimulus is
emulated by this channel. The rotary switch S1 is used to select
this channel. When the channel is selected, LED D101 will light
to indicate that the correct channel is selected.

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Bridge Sensitivity vs Temp

-1.0E-03

-5.0E-04

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

3.5E-03

4.0E-03

4.5E-03

-50 0 50 100 150

Temp, degC

Kbr idge, V/V

offset
span

This is another example illustrating how a particular
channel on the sensor emulator represents an
applied stimulus and temperature combination for the
sensor. In this example, the sensor output at cold
temperature and 100% of applied stimulus is
emulated by this channel. The rotary switch S1 is
used to select this channel. When the channel is
selected, LED D103 will light to indicate that the
correct channel is selected.

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The second tab in the Generate_Sim_Values.xls spreadsheet allows the user to enter the temperature
range and room temperature diode voltage (light blue areas). Thespreadsheet calculates the diode
voltages and displays the results in the yellow areas. Note thatthe Temp ADC areas are specific to the
PGA309 sensor signal conditioning chip. The Temp ADC values willbe used in the computation of the
Counts for the temp ADC. The next several pages will show how the diode voltages are used to program
the sensor Sensor-Emulator-EVM.

Adjust the Diode section
potentiometer on the
Sensor-Emulator-EVM to
generate the counts as
detailed on page 38.

PGA309 Temp ADC

generate_sim_values.xls

Diode Vo Tab

Diode Vo: Generate Diode Voltages
based on Operating Temperature Range

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Note when emulating Diode
temperature control, the Rt
temperature section is not used.

Each channel on the bottom section of the Sensor­Emulator-EVM represents the output of the
emulated temperature sensor. Using the Temp
DVM, adjust the respective potentiometers, coarse
first, the fine, to match the values computed by the
Generate_Sim_Values.xls spreadsheet for
Diode/Cold, Diode/Room, and Diode/Hot. For this
example, the temperature output signal at cold
temperature (-45oC) is emulated by this channel.
The rotary switch S2 is used to select this channel.
When the channel is selected, LED D201 will light
to indicate that the correct channel is selected.

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Step 5: Use the PGA309
Calibration Spreadsheet

•Select the calibration algorithm

•Copy the PGA309 registers into the spreadsheet

•Use the Sensor-Emulator-EVM to generate the
sensor outputs over temperature.

•Store calibration results into a file. Load this into
the PGA309 external EEPROM.

•Measure the post-calibration error. Perform a
second calibration to improve accuracy.

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For this example, use the PGA309 Calibration Spreadsheet. This tool uses
measured data (pressure and temperature) to create a lookup table that the
PGA309 will use to compensate for offset and gain drift. The spreadsheet will
also generate a coefficient that the PGA309 will use to correct for nonlinearity
verses applied pressure. Note: you will need to enable macros and load the
analysis toolpackto get this Excel sheet to work properly. Information
regarding configuration of Excel is detailed in the PGA309EVM Users’Guide.

When you bring up the spreadsheet, it will
ask you if you want to start the program.
Press No, because the program should
already be up from Step 2.

PGA309 Calibration
Spreadsheet, Main Tab

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Press Load

registers from
PGA309 to copy

the registers
from the
evaluation
fixture into the
spreadsheet.

PGA309 Calibration
Spreadsheet, Main Tab

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Press Prepare Calibration Sheet to select
the algorithm. In this example, we will do a
3 temperature3 pressure calibration.

Press OK after you have
selected 3 Temperature 3
Pressure calibration.

PGA309 Calibration
Spreadsheet, Main Tab

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Next the program will ask what
type of Temperature
Measurement Method you want
to use. For this example, we use
the diode method.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

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When the template for your
calibration algorithm is loaded
this box will pop up.
Press OK.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

45

When the Load registers from
PGA309 button on the Main
sheet was pressed, the
PGA309 registers were copied
into this section of the Sensor
Curvefit sheet.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

46

The appropriate values need to be
entered manually for the measurement
temperatures. The measurement
temperatures are the temperatures that
the calibration measurements are made
at.

The appropriate values need to be
entered manually for the temperature
range. This is the range that the curve fit
is done over. Enter the values shown for
our example.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

47

The easiest way of doing
this is to select a cell and
press the Insert

TempADCreading in
active cell button. This

will insert a PGA309
Temp ADC in counts into
that cell.

The measured PGA309 Temp
ADC readings need to be
recorded at the respective
applied temperatures. Use the
temperature selector switch on
the Sensor-Emulator-EVM to
generate room,hot,and cold
readings for this example.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

48

The easiest way of
doing this is to select a
cell and press the Insert

Voutreading in active
cell button. This will

insert a PGA309 output
voltage reading from the
ADS1100 delta sigma
ADC into that cell.

The PGA309 output voltage needs to
be recorded at the appropriate
applied pressure and temperature.
Use the bridge selector switch on the
Sensor-Emulator-EVM to generate
the respective room (0%, 50%,
100%), hot (0%, 25%, 50%, 75%,
100%), and cold (0%, 50%, 100%).

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

49

After the calibration
measurements are
complete look at the
graphs located on
the sensor Curvefit
sheet. These
graphs are an easy
way to check for
gross problems.
The graphs shown
are indicative of
typical results for
example.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

50

Enter the output
voltage scale, the
number of points
in the table, and
the look up table
temperature
range. For our
example, enter
the values shown.

PGA309 Calibration

Spreadsheet, Calibration

Results Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

51

Range3: This is the range of
measurements made during
calibration. This range must be a
subset of Range1. It is OK for range 1
and range 3 to be equivalent.

Range1: This is the range of
the mathematical model of the
sensor that is developed by
the spreadsheet.

Range2: This is the range that the
look up table is developed over. This
range must be a subset of Range1. It
is ok for Range2 and Range3 to be
equivalent. This range over which the
calibrated sensor will correct for
temperature drift.

Note about the temperature ranges

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

PGA309 Calibration

Spreadsheet, Calibration

Results Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

52

The Result

Sanity Check

will flag any
problems with
gain and offset
ranges in the
calibration
table.

The Voutmax and min
calibrated result graph gives
an idea of what errors you will
see based on the resolution
of internal components. Note
the output should
approximately match the
values entered in the Enter
Output Scale section.

PGA309 Calibration

Spreadsheet, Calibration

Results Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

53

The calibration table
that will be loaded into
the EEPROM is
displayed on the
Calibration Results tab
on the spreadsheet. At
this point the initial
calibration is complete
and the table can be
uploaded into the
PGA309 EEPROM.

PGA309 Calibration

Spreadsheet, Calibration

Results Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

54

Press the Save Registers + Lookup Table button. This will
store the lookup table into a file that can be loaded into the
PGA309 EEPROM.

PGA309 Calibration

Spreadsheet, Main Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

55

Step B

Make sure the PGA309 Test Pin
High box is not checked. When in

this mode the PGA309 will read the
EEPROM and adjust offset and
gain for each temperature
conversion

Step D

Press the Read PGA309 to see
the updated register values.

After Step D, the initial
calibration is complete.

Step C

Press Write EEPROM to
store the lookup table in
the external EEPROM .

Step A

Press the Open File
button to get the file
containing the
calibration results.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

56

The initial post
calibration results will
typically have errors
ranging from 0.1% to

0.3%.

The PGA309 Error tab on the
generate_sim_values.xls is a
convenient way to do a post calibration
error analysis. To use it select the
blue cell corresponding to the current
setup, and press the Insert Vout
reading in active cell button. This will
insert the PGA309 output reading from
the ADS1100.

generate_sim_values.xls,

PGA309 Error Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

57

The post first
calibration results are
made at room
temperature and
entered here. For this
example, use the
Sensor-Emulator-EVM
to generate 0% and
100% pressure at
room temperature.

Note the correction
factors are
developed based
on these readings.
These are used to
calibrate the
Lin_Dacerrors not
previously
accounted for.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

58

The final calibration is
complete at this point

After making the secondary
calibration measurements,
store the calibration results
into a file and load them into
the PGA309 as with the first
calibration. The file for this
example calibration is saved
on the PGA309 Quick Start
Disk and is called
quick_start_second.txt.
Your results should be
similar to this file.

PGA309 Calibration

Spreadsheet, Main Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

59

The secondary
calibration can be
done to significantly
reduce the error. Post­secondary calibration
errors are typically on
the order of 0.05%.
The secondary
calibration involves
making two
measurements at
room temperature.

generate_sim_values.xls,

PGA309 Error Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

60

PGA309 Ratiometric
Calibration Example

This example walks through the PGA309 ratiometric calibration technique.
The PGA309 Absolute Calibration example is a more detailed description of a
calibration, and so, it is recommended that you review this example first. This
document describes the key elements that are required in a ratiometric
calibration, but does not fully explain how to use the PGA309 Gain Calculator,
Sensor-Emulator-EVM, or the Designers Kit Control Program.

For information on these development tools, please see the PGA309 Product
Folder on the TI website, at www.ti.com.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

61

This is the hardware
configuration that this
ratiometric calibration example
details. In this example, the
Sensor-Emulator-EVM is used
to emulate the bridge sensor
and the Diode. Note that the
device power supply is used to
provide excitation for the
sensor. So for this
configuration, the Vexcpin on
the PGA309 is not used and
consequently, the PGA309
cannot correct for nonlinearity
verses applied stimulus.
Temperature nonlinearities of
span and offset will still be
corrected.

Vexc

Vin+

Vin-

Temp

PGA309

Vsa

5

V

GND

Ref_In/

Ref_Out

Real World Inputs

PGA309 Ratiometric
Example

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

62

This diagram illustrates PGA309EVM jumper settings for a ratiometric system.
Sensor-Emulator-EVM connections and power connections are also shown.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

63

Required Electrical Connections to
Sensor-Emulator-EVM

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

64

These jumpers must
be set to the position
shown to allow the
on-board voltage
reference to generate
the emulated diode
voltages.

These three channels
are used to set the
temperature output
signal in the diode
mode. The Rt
channels are not used
in this mode.

Set the jumper
JUMP1 to the
position shown to
connect the Diode
temperature
emulation.

Set the jumper
JUMP5 to the
position shown to
connect GND to
the bottom of the
bridge emulator.

Sensor-Emulator-EVM Jumper Setup

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

65

The PGA309 Calculator can be
used to compute the gain and
offset settings for the PGA309.
These are the values used for
this ratiometric example
configuration.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

66

In the ratiometric configuration, the power supply (Vs) is beingused as the
reference. Thus, it is very important that the supply is measured during calibration.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

67

Configure the initial settings of the PGA309

Step B

The gain and offset values
computed by the calculator need
to be written into the PGA309
using the PGA309 Designer’s Kit
Control Program.

Step A

During calibration, the PGA309
Test Pin High must be checked to

prevent the PGA309 from reading
the EEPROM during calibration.

Step C

The value measured for Vs must
be typed in here. After all the
values are entered, press Write
PGA309.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

68

The configuration shown was selected
for this example (diode measurement
using the built-in 2.048V reference). It
is important to use the built in ADC
reference because the diode
measurement is absolute and all the
other references are relative to the
power supply for this configuration.

Configure the Temp ADC as
shown and click OK. From the
main window, press Write
PGA309.

Set up the PGA309
Temperature ADC

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

69

The sensor’s raw output is computed
and displayed here. These values are
used to setup the sensor emulator. The
sensor emulator EVM will need to be
adjusted to these levels.

The sensor specifications are
entered here. The definitions of
the different parameters is
described earlier in this document.

Note that Vexc= Vs for
ratiometric.

Enter these for our
example.

Note that Pressure Nonlin is zero. The sensor
must be linear for this configuration because the
sensor excitation is the power supply and so the
nonlinearity correction circuit cannot be used.

generate_sim_values.xls,

Offset and Span Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

70

When the sensor’s specifications
have been entered, the
spreadsheet will display the bridge
output versus temperature.

The bridge output versus applied
stimulus is also displayed. This
must be a linear function for a
ratiometric setup that does not use
Vexcfor bridge excitation.

generate_sim_values.xls,

Offset and Span Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

71

Bridge Sensitivity vs Temp

-1.0E-03

-5.0E-04

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

3.5E-03

4.0E-03

4.5E-03

-50 0 50 100 150

Temp, degC

Kbr idge, V/V

offset
span

Each channel on the top section of the sensor emulator
represents a applied stimulus and temperature combination
for the sensor. Adjust the potentiometers coarse first, then
fine, to match the values computed by the
Generate_Sim_Values.xls spreadsheet for cold (0%. 50%,
100%), room (0%, 25%, 50%, 75%, 100%), and hot (0%,
50%, 100%). For example, the sensor output at cold
temperature and 0% of applied stimulus is emulated by this
channel. The rotary switch S1 is used to select this channel.
When the channel is selected, LED D101 will light to indicate
that the correct channel is selected.

For this ratiometric example adjust
the potentiometer on the Sensor­Emulator-EVM to the bridge
section to produce the respective
voltages shown.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

72

Note when emulating Diode
temperature control, the Rt
temperature section is not used.

Each channel on the bottom section of the Sensor­Emulator-EVM represents the output of the
emulated temperature sensor. Using the Temp
DVM adjust the respective potentiometers, coarse
first, the fine, to match the values computed by the
Generate_Sim_Values.xls spreadsheet for
Diode/Cold, Diode/Room, and Diode/Hot. For this
example, the temperature output signal at cold
temperature (-45oC) is emulated by this channel.
The rotary switch S2 is used to select this channel.
When the channel is selected, LED D201 will light
to indicate that the correct channel is selected.

This is the Diode Vo tab on the

Generate_Sim_Values.xls

spreadsheet.

It is used to compute diode voltages that are
used to set up the Sensor-Emulator-EVM.

For this ratiometric example, adjust the
potentiometer on the Sensor-Emulator­EVM to the diode temperature section to
product the respective counts shown for
temperature.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

73

Press Load

registers from
PGA309 to copy

the registers
from the
evaluation
fixture into the
spreadsheet.

For this ratiometric example, use the PGA309 Calibration Spreadsheet. This
tool uses measured data (pressure and temperature) to create a lookup table that
the PGA309 will use to compensate for offset and gain drift. The spreadsheet will
also generate a coefficient that the PGA309 will use to correct for nonlinearity
verses applied pressure. Note: you will need to enable macros and load the
analysis toolpackto get this Excel sheet to work properly. Information
regarding configuration of Excel is detailed in the PGA309EVM Users Guide.

PGA309 Calibration

Spreadsheet, Main Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

74

Press Prepare Calibration Sheet to select
the algorithm. In this example, we will do a
3 pressure 3 temperature calibration.

Press OK after you have
selected 3 Temperature 3
Pressure calibration.

PGA309 Calibration

Spreadsheet, Main Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

75

Next, the program will ask
what type of Temperature
Measurement Method you
want to use. For this example,
we use the diode method.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

76

This are contains the PGA309 settings. These settings
are loaded into these cells when the Load Registers From
PGA309 button was pressed from the main tab.

The temperature
ranges and pressure
ranges need to be
entered by hand.

The TempADC
readings and
VoutMeasvalues
need to be
measured. This can
be done using the

Insert TempADC
reading in active cell
and Insert Vout
reading in active cell

buttons.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

77

Note that the 3 pressure 3 temperature calibration algorithm
will compute values for nonlinearity error. This value needs
to be very small for this configuration because nonlinearity
correction is not used. This value will not be used to
generate the calibration tables in the EEPROM.

The value of Klinstored in the
EEPROM will be zero for this mode
because Vexcis disabled.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

78

For the ratiometric calibration method,
the secondary calibration is not
necessary. The secondary calibration is
used to correct for errors introduced by
the LinDac. So, for this example, this
section is left blank.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

79

Select the desired
post-calibration
output range.

Select the
temperature range of
the look-up-table.

Make sure the Result
Sanity Check passes.

PGA309 Calibration

Spreadsheet, Calibration

Results Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

80

Press Save
Registers+LookupTable.

The spreadsheet will let you know that
Excitation is Disabled. This is normal
for the ratiometric method.

PGA309 Calibration

Spreadsheet, Main Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

81

Step B

Make sure the PGA309 Test Pin High
box is not checked. When in this
mode, the PGA309 will read the
EEPROM and adjust offset and gain for
each temperature conversion

Step D

Press the Read PGA309 to see the
updated register values.

Step C

Press Write EEPROM to
store the table on the
EEPROM .

Step A

Press the Open File
button to get the file
containing the
calibration results.

After Step D, the calibration is
complete.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

82

The post-calibration
results will typically have
errors less than 0.1%.

The PGA309 RatioMetricError tab on
the generate_sim_values.xls is a
convenient way to do a post-calibration
error analysis. To use it, select the
blue cell corresponding to the current
setup, and press the Insert Vout
reading in active cell button. This will
insert the PGA309 output reading from
the ADS1100. This spreadsheet page
provides for error calculations at two
different power supply voltages. The
initial supply is Vs= 4.963V (you need
to enter your measured Vs).

generate_sim_values.xls,

PGA309 Ratiometric

Error Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

83

For the ratiometric calibration
method it is useful to adjust the
power supply to see how PSR
affects the PGA309 calibrated
accuracy. A 10% power supply
deviation is used in this example
because it is a typical worst case
deviation for ratiometric systems.
Connecting a 53kΩ resistor
between the 3V pin and the
center pin on JA will cause the
power supply to shift from 5V to

4.5V. You can adjust the value of
the shunt resistance to get more
or less power supply deviation.
A short will cause the power
supply to deviate from 5V to 3V.

Vout

ADJ

GND

Vin

Vin

NC

EN

Vout

53k

3V

JA

5V

JA

JB

JF

JC

JD

JE

VOUT

5V

PROG

3V

PC

1PU

INPU

ON

SDN
RTS

DTR

DIS

PGA309 PC Interface Board

To PC

Serial

Port

6V dc Power

from wall

adaptor

53k

Schematic

Mechanical Diagram

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

84

Make sure that you measure the
supply voltage (Vs) and enter it into
the PGA309 Designer’s Kit Control

Program.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

85

Make sure that you
measure the supply voltage
(Vs) and enter it into the

PGA309 Designer’s Kit
Control Program.

Measure the PGA309 post calibration error
at a different supply voltage to see the
affect of PSR on error. For this example,
the supply was changed from Vs= 4.963V
to Vs=4.457V and the average error
changed from -0.06% to -0.03%.

generate_sim_values.xls,

PGA309 Ratiometric

Error Tab

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

86

PGA309 With Output Scaling

(0 to 10V)

V

o

R

f

R

1

R

f

R

2

+ 1+













Vin⋅

R

f

R

1













V

ref

⋅−

VoExtraGain( )Vin⋅ ExtraOffset( )V

ref

⋅+

In many applications an external gain stage is used to get an output swing beyond the range of the
PGA309. The circuit shown below is a typical example of gain scaling with an offset shift. The PGA309
calibration spreadsheet can accommodate external gain and offsetscaling. Doing the calibration by
measuring the output of the external gain stage will calibrate out errors caused by resistor tolerance in the
external stage.

+

-

R1

R2

Rf

Vref

Vo

PGA309

Vin

Vout

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

87

PGA309 With Output Scaling

(0 to 10V)

This calculation shows how
the example configuration
shown on the previous page
can be used to take the 0.5V
to 4.5V output of the PGA309
and re-scale it to 0V to 10V.

This equation must be broken
down into an “ExtraGain”and
“ExtraOffset”factor for the
spreadsheet.

ExtraOffset 0.5−=

ExtraOffset

Rf−

10103⋅

:=

ExtraGain 2.5=

ExtraGain

R

f

R

1

R

f

R

2

+ 1+













:=

For the spreadsheet you need to break the function into "extra gain" and "extra
offset" as shown below.

Rf5000.

Substitute the value of R2 into
equation 2 to solve for Rf

R25000.

Substitute equation 2 into
equation 3 and solve for R2

Equation 3: Vin=4.5V, Vo = 10V

10

R

f

10103⋅

R

f

R

2

+ 1+













4.5⋅

R

f

10103⋅













2.5⋅−

Equation 2: solve Equation 1 for Rf

Rf2500.

R

2

R22500.−

⋅

Equation 1: Vin = 0.5V, Vo = 0V

0

R

f

10103⋅

R

f

R

2

+ 1+













0.5⋅

R

f

10103⋅













2.5⋅−

R110103⋅:=

Let

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

88

PGA309 With Output Scaling

(0 to 10V)

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

The “ExtraGain”and
“ExtraOffset”factor are
entered here on the
spreadsheet. Normally these
are set to ExtraGain= 1.0 and
ExtraOffset= 0.0.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

89

PGA309 With Output Scaling

(0 to 10V)

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

The data that is measured at
the output of the external
amplifier is entered directly
into the spreadsheet.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

90

PGA309 With Output Scaling

(0 to 10V)

The output range must be
include the scaling stage.

PGA309 Calibration

Spreadsheet, Calibration

Results Tab

Other then these few minor
changes, the calibration
method is the same as the
other examples.

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

91

I

outIinIref

+

(

)

100⋅

I

out

V

in

R

1

V

ref

R

2

+













100⋅

I

out

100

R

1





Vin⋅

100

R

2





V

ref

⋅+

I

out

ExtraGain( )Vin⋅ ExtraOffset( )2.5⋅+

The spreadsheet can also be used to calibrate a system using a PGA309 with a 4mA to 20mA output
scaling.

PGA309 With Output Scaling

(4mA to 20mA)

SBOA103C
Jan 2006

PGA309 Quick Start

System Reference Guide

92

4103−⋅

0.5
R

1

2.5
R

2

+







100⋅

Equation 1: Vin = 0.5V, Iout = 4mA

R112500.

R

2

R262500.−

⋅

Equation 2: solve Equation 1 for R1

20103−⋅

4.5
R

1

2.5
R

2

+







100⋅

Equation 3: Vin=4.5V, Iout = 20mA

Substitute equation 2 into
equation 3 and solve for R2

R2125103⋅

Substitute the value of R2 into
equation 2 to solve for R1

R125103⋅

For the spreadsheet you need to break the function into "extra gain" and "extra
offset" as shown below.

I

out

100

R

1





Vin⋅

100

R

2





V

ref

⋅+

I

out

100

25103⋅













Vin⋅

100

125103⋅













2.5⋅+

I

out

ExtraGain( )Vin⋅ ExtraOffset( )2.5⋅+

I

out

4 103−×

( )

Vin⋅ 800 106−×

( )

2.5⋅+

This calculation shows how
the example configuration
shown on the previous page
can be used to take the 0.5V
to 4.5V output of the PGA309
and re-scale it to 4mA to
20mA.

This equation must be broken
down into an “ExtraGain”and
“ExtraOffset”factor for the
spreadsheet.

PGA309 With Output Scaling

(4mA to 20mA)

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The “ExtraGain”and
“ExtraOffset”factor are
entered here on the
spreadsheet. Normally these
are set to ExtraGain= 1.0 and
ExtraOffset= 0.0.

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

PGA309 With Output Scaling

(4mA to 20mA)

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The data that is measured at
the output of the voltage to
current converter is entered
directly into the spreadsheet
(in Amps).

PGA309 Calibration

Spreadsheet, Sensor

CurvefitTab

PGA309 With Output Scaling

(4mA to 20mA)

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The output range must be
include the scaling stage (in
Amps).

Other then these few minor
changes, the calibration
method is the same as the
other examples.

PGA309 Calibration

Spreadsheet, Calibration

Results Tab

PGA309 With Output Scaling

(4mA to 20mA)

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PGA309 In Three Wire Mode

In many cases the PGA309 is connected in a configuration referred to as a three wire connection. In this
configuration the only wires that need to connect to the sensor module are power, ground, and Vout. In
this configuration the One-Wire digital communication line is connected to the Voutpin. When the
PGA309 is initially powered up, the Voutpin is placed in a high impedance mode for 15mS. If
communication is established using the One-Wire during this time, the PGA309 will keep Voutin high
impedance until the communications is complete. After the communication is complete the PGA309 Vout
pin will become active and remain active until power is cycled again. While using the EVM to
communicate in Three Wire Mode, the EVM will cycle power before each One-Wire communication.

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PGA309 In Three Wire Mode

If the “Set PreCalEE”feature is used the test pin is normally grounded (leave “PGA309 Test Pin
HIGH”box unchecked).

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PGA309 In Three Wire Mode

A key technique used in calibration is to use the test pin on the PGA309. The test pin is typically used
during calibration to place the PGA309 into test mode. The mainbenefit of test mode is that the Gain
DAC and Offset DAC are forced to remain at the last values written to their respective registers.

In the case of three wire mode the test pin is grounded and cannot be used. In this case, an EEPROM
table can be built that will force that Gain DAC and Offset DAC to be constant. The PGA309 Designers
Kit Control Program “Set PrecalEE”feature simplifies the creation of this table.

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PGA309 In Three Wire Mode

When using this feature, first set all the registers to values your application requires. Then press the “Set
PreCalEE”button.

Step 1

Step 2

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PGA309 In Three Wire Mode

After Pressing the “Set PreCalEE”a dialogue box will pop up that verifies the value of the Zero DAC and
Gain Dacyou want in your EEPROM configuration. After creating the EEPROM table, the PGA309
Designer’s Kit Control Program is ready for to be used with the calibration spreadsheet.

After pressing
Generate and
Write EEPROM
Table, the lookup
table will be
updated to force a
constant Gain
Dacand Zero Dac
for PreCal
settings.