CN-0287: Fully Isolated 4-Channel, Temperature Measurement Circuit Optimized...

CN-0287: Fully Isolated 4-Channel, Temperature Measurement Circuit Optimized...
Circuit Note
CN-0287
Devices Connected/Referenced
Circuits from the Lab® reference designs are engineered and
tested for quick and easy system integration to help solve today’s
analog, mixed-signal, and RF design challenges. For more
information and/or support, visit www.analog.com/CN0287.
AD7193
4-Channel, 4.8 kHz, Ultralow Noise,
24-Bit Sigma-Delta ADC with PGA
ADT7310
±0.5°C Accurate, 16-Bit Digital SPI
Temperature Sensor
AD8603
Precision Micropower, Low Noise
CMOS R-to-R Input/Output
Operational Amplifiers
ADR3440
4.096 V, Micropower High Accuracy
Voltage Reference
ADG738
CMOS, Low Voltage, 3-Wire SeriallyControlled, Matrix Switch
ADG702
CMOS Low Voltage 2 Ω SPST Switch
AD5201
33-Position Digital Potentiometer
ADuM1280
3 kV RMS Dual Channel Digital
Isolators
ADuM5401
Quad-Channel, 2.5 kV Isolators with
Integrated DC-to-DC Converter
Isolated 4-Channel, Thermocouple/RTD Temperature Measurement
System with 0.5°C Accuracy
EVALUATION AND DESIGN SUPPORT
Circuit Evaluation Boards
CN-0287 Circuit Evaluation Board (EVAL-CN0287-SDPZ)
System Demonstration Platform (EVAL-SDP-CB1Z)
Design and Integration Files
Schematics, Layout Files, Bill of Materials
CIRCUIT FUNCTION AND BENEFITS
The circuit shown in Figure 1 is a completely isolated 4-channel
temperature measurement circuit optimized for performance,
input flexibility, robustness, and low cost. It supports all types of
thermocouples with cold junction compensation and any type
of RTD (resistance temperature detector) with resistances up to
4 kΩ for 2-, 3-, or 4-wire connection configurations.
The RTD excitation current are is programmable for optimum
noise and linearity performance.
RTD measurements achieve 0.1°C accuracy (typical), and
Type-K thermocouple measurements achieve 0.05°C typical
accuracy because of the 16-bit ADT7310 digital temperature
sensor used for cold-junction compensation. The circuit uses a
four-channel AD7193 24-bit sigma-delta ADC with on-chip
PGA for high accuracy and low noise.
Input transient and overvoltage protection are provided by low
leakage transient voltage supressors (TVS) and Schottky diodes.
The SPI-compatible digital inputs and outputs are isolated
(2500 V rms), and the circuit is operated on a fully isolated
power supply.
Rev. C
Circuits from the Lab® reference designs from Analog Devices have been designed and built by Analog
Devices engineers. Standard engineering practices have been employed in the design and
construction of each circuit, and their function and performance have been tested and verified in a lab
environment at room temperature. However, you are solely responsible for testing the circuit and
determining its suitability and applicability for your use and application. Accordingly, in no event shall
Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due
toanycausewhatsoeverconnectedtotheuseofanyCircuitsfromtheLabcircuits. (Continuedonlastpage)
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©2013–2014 Analog Devices, Inc. All rights reserved.
CN-0287
Circuit Note
+5V
: ANALOG GROUND
VDD
+4.096V
0Ω
AD5201
+5V
A
COLD JUNCTION COMPENSATION
+5V
SCLK
CT
INT
ADT7310 CS
SCLK
DOUT
GND
DIN
: DIGITAL GROUND
W
ADG738_CS
SCLK
DIN
VSS
R3
ADG738
V+
D
VOUT
C2
C2
GND
D
P3
S8
IN
300Ω
1.69kΩ
AD7193
1nF
JP1
300Ω
1.69kΩ
CS
CH 4
SCLK
SCLK
AIN4
DOUT
DOUT
DIN
+5V
+5V 300Ω
JP4
1
ADT7310_CS
DIN
2
300Ω
INTISO
CTISO
27nF
10µF
+5V
DVDD
REFIN2(+)
DGND
REFIN2(–)
AINCOM
GND2
VOA
GND1
VIA
VIB
GNDISO
ADT7310_CS ISO
ADG738_CS ISO
+5VISO
SCLK
AD7193_CS
DOUT
GNDISO
VOA
VDD1
GND1
VIA
VOA
VIB
VOC
VIC
VID
VOD
GNDISO
DINISO
SCLKISO
AD7193_CS ISO
DOUTISO
ADuM5401
10926-001
4.02kΩ
0.1%
10ppm
VDD1
VISO
DIN
AIN8
1nF
+5VISO
VDD2
+5V
0.1µF
+5V
300Ω
GNDISO
ADuM1280
AGND
3
1.69kΩ
VOB
VOB
ADG738_CS
AVDD
AIN7
RTD 4W
1.69kΩ
GND2
VOA
+5V
+5V
1nF
4
AD7193_CS
AIN3
AIN6
1.69kΩ
GND1
VIA
AIN2
1nF
AIN5
2
VDD2
ADuM1280
THERMOCOUPLE:
RTD 2,3W
1
VDD1
VIB
CT
27nF
1
2
3
INT
AIN1
+5V 300Ω
1.69kΩ
+5VISO
+5V
P2
+5V
2
4
FORCE
SENSE
REFIN1(+) REFIN1(0)
S
+5V 300Ω
CH 1
3
FORCE
SENSE
ADG702
S7
3
5.6V
ZENER DIODE
+5V
300Ω
1.69kΩ +5V
1
DIN
CS
ADR3440
C2
V–
S2
1.69kΩ
PWR-ON
PRESET
SCLK
+4.096V
1kΩ
AD8603
+5V 300Ω
GND
SDI
+5V
+5V
SYNC SCLK DIN DOUT
S1
1.69kΩ
CLK
B
CT
INT
ADT7310_CS
SCLK
DOUT
DIN
+5V
SHDN
LOGIC
CONTROL
Figure 1. 4-Channel Thermocouple and RTD Circuit (Simplified Schematic: All Connections and Decoupling Not Shown)
CIRCUIT DESCRIPTION
signal generated is typically from several microvolts to tens of
millivolt depending on the temperature difference.
Temperature Measurement Introduction
Thermocouples and RTDs (resistance temperature detectors)
are the most frequently used sensors for temperature
measurement in industrial applications. Thermocouples are
able to measure very high temperatures up to about +2300°C
and also have a fast response time (measured in fractions of a
second). RTDs are capable of higher accuracy and stability than
thermocouples, and the resistance of long wire lengths
(hundreds of meters) to a remote RTD can be compensated for
with 3- or 4-wire connections.
A thermocouple consists of two wires of different metals joined
at one end. This end is placed at the temperature which is to be
measured, refered to as the measurement junction. The other
end is connected to a precision voltage measurement unit, and
this connection is referred to as the reference junction or alternately
the cold junction. The temperature difference between the
measurement junction and the cold junction generates a voltage
(known as the Seebeck effect voltage) that is related to the
difference between the temperatures of the two junctions. The
For example, K-type thermocouples are capable of measuring
−200°C to +1350°C with an output range of approximately −10
mV to +60 mV. It is important for the signal chain to maintain
as high impedance and low leakage as possible to achieve the
highest accuracy for the voltage measurement. In order to
convert this voltage to an absolute temperature, the cold junction
temperature must be accurately known. Traditionally 1°C to 2°C
has been considered sufficient, although since the cold junction
measurement error contributes directly to the absolute
temperature error, a higher accuracy cold junction temperature
measurement is beneficial
An RTD is made from a pure material, such as platinum, nickel
or copper, that has a predictable change in resistance as the
temperature changes.The most widely used RTD is platinum
(Pt100 and Pt1000).
One method used to accurately measure the resistance is to
measure the voltage across the RTD generated by a constant
current source. Errors in the current source can be cancelled by
referring the measurement to the voltage generated across a
Rev. C | Page 2 of 9
Circuit Note
CN-0287
For the industrial field applications both high performance as
well as protection against both high-voltage transient events and
dc over-voltage conditions are important design considerations.
How this Circuit Works
The circuit shown in Figure 1 is designed for precision
temperature measurement applications in the industrial field
environment and is optimized for flexibility, performance,
robustness, and cost. This circuit uses the AD7193, low noise,
24-bit sigma-delta ADC to ensure high resolution and linearity
for the entire circuit.
Programmable Current Source for RTDs and Bias
Voltage Generator Circuit for Thermocouples
RTD measurements require a low noise current source that
drives the RTD and a reference resistor. Thermocouple
measurements, on the other hand, need a common-mode bias
voltage that shifts the small thermocouple voltage into the input
range of the AD7193. The circuit shown in Figure 2 meets both
requirements and utilizes the AD8603 a low noise CMOS railto-rail input/output op amp with only 1 pA maximum input
bias current and 50 μV maximum offset voltage, combined with
the ADG702 single channel, CMOS low voltage 2 Ω SPST
switch, and the ADG738 eight-channel matrix switch.
+4.096V
+5V
ADG738
S1
A
R3
D
AD8603
The AD5201, 33-position digital potentiometer, AD8603 op
amp, and ADG702 single channel switch constitute a simple
programmable current source and bias voltage buffer for the RTD
and thermocouple measurements. The ADG738 routes the
current source to the active RTD channel and allows wire
resistance compensation for the 3-W RTD configuration.
VW
AD5201
W
1kΩ
B
C2
IEXC
S
D
ADG702
RTD
AD7193
AIN1
The ADT7310 digital SPI temperature sensor has ±0.8°C
maximum accuracy (+5 V supply) from −40°C to +105°C and is
used for cold-junction compensation for the thermocouple
measurement. The ADR3440 is a low noise and high accuracy
4.096 V reference connected to REFIN1(+)/REFIN1(−) of the
AD7193 for the thermocouple measurements.
TC
AIN2
IEXC =
VW
RREF
REFIN2(+)
RREF
REFIN2(–)
10926-002
reference resistor that is driven with the same current (i.e. a
ratiometric measurement). Minimizing the leakage current
through the current path is important for achieving high accuracy
because the excitation current is typically only a few hundred
microamps to prevent self heating.
Analog-to-Digital Converter
Figure 2. External Programmable Current Source and Bias Voltage Generator
The AD7193 is a low noise, complete analog front end for high
precision measurement applications. It contains a low noise, 24bit sigma-delta (Σ-Δ) analog-to-digital converter (ADC). This
ADC achieves high resolution, low non-linearity, and low noise
performance as well as very high 50 Hz/60 Hz rejection. The
data output rate can be varied from 4.7 Hz (24 bits effective
resolution, Gain = 1), to 4.8 kHz (18.6 bits effective resolution,
Gain = 1). The on-chip low noise PGA amplifies the small
differential signal from the thermocouple or RTD with a gain
programmable from 1 up to 128, thereby allowing a direct
interface. The gain stage buffer has high input impedance and
limits the input leakage current to ± 3 nA maximum. The gain
of theAD7193 must be configured properly depending on the
temperature range and type of sensors. The on-chip multiplexer
allows four differential input channels to be shared with the
same ADC core, saving both space and cost.
With the ADG738 opened and the ADG702 closed, the
AD8603 acts as a low noise, low output impedance unity-gain
buffer for the thermocouple application. The voltage from the
AD5201 digital potentiometer is buffered and is used for the
thermocouple common-mode voltage, usually 2.5 V, which is
one-half the supply voltage. The 33-position AD5201 digital
potentiometer is driven with the ADR3440 low drift (5 ppm/°C)
4.096 V reference for accuracy.
With the ADG738 closed and the ADG702 opened, the
AD8603 generates the RTD excitation current, IEXC = VW/RREF.
Rev. C | Page 3 of 9
CN-0287
Circuit Note
Temperature measurement is a high precision and low speed
application, therefore there is adequate settling time available to
switch the single current source between all 4 channels,
providing excellent channel-to-channel matching, low cost, and
small PCB footprint.
With S1 of the ADG738 closed and S2 opened, the voltage at
the input of AD7193 is V1. With S1 opened and S2 closed, the
voltage on the input of AD7193 is V2, The voltage across the
RTD sensor is VRTD, the exciting current from the current source is
IEXC. V1 and V2 contain the error generated by the lead resistance
as shown below:
The ADG738 is an 8-to-1 multiplexer that switches the current
source between channels. In order to support the 2-, 3-, and 4wire RTD configurations, each of the four channels need two
switches.
In many applications, the RTD may be located remotely from
the measurement circuit. The resistance from the long lead
wires can generate large errors, especially for low resistance
RTDs. In order to minimize the effect of the lead resistance, a 3wire RTD configuration is supported as shown in Figure 3.
+5V
S2
AD7193
RW2
AIN1
+5V
JP[x]
RTD
IEXC
RW3
REFIN2(+)
RREF
Figure 3. Connector and Jumper Configuration for3-Wire RTD Sensor
RTD
JPx
1
JPx
JPx
1
3
2
3
4
3
3
4
4
CNx
2
3
RTD
THERMOCOUPLE
1
2
3
(5)
1
1
1
RRTD = VRTD/IEXC = (2V1 – V2)/IEXC
2
2
2
(4)
CNx
CNx
1
VRTD = 2V1 – V2
RTD 4-WIRE
RTD 3-WIRE
CNx
(3)
Figure 4 summarizes the connector configuration and jumper
placements for RTD 2-wire, RTD 3-wire, RTD 4-wire, and
thermocouple applications.
10926-003
REFIN2(-)
RTD 2-WIRE
V RTD = R RTD × I EXC
The 4-wire RTD connection requires two extra sense lines, but
is insensitive to wiring resistances and only requires one
measurement.
AIN2
RRTD
(2)
RTD
+
TC
–
Figure 4. Connector Configuration and Jumper Placements for EVAL-CN0287-SDPZ Board
Rev. C | Page 4 of 9
JPx
2
1
3
2
4
3
10926-004
IEXC
V 2 = ( R W2 + R RTD + R W3 ) × I EXC
Equation 5 shows that the 3-wire configuration requires two
separate measurements (V1 and V2) in order to calculate RRTD,
thereby decreasing the output data rate. In most applications
this is not a problem.
CURRENT SOURCE
D
S1
(1)
Assuming RW1 = RW2 = RW3 and combining Equations 1, 2, and 3
yields:
ADG738
RW1
V 1 = ( R RTD + R W3 ) × I EXC
Circuit Note
CN-0287
Protection Circuits
Thermocouple Configuration Test Results
Transient and overvoltage conditions are possible both during
manufacturing and in the field. To achieve a high level of
protection, additional external protection circuitry is necessary
to compliment the IC’s internal integrated protection circuitry.
The external protection adds additional capacitance, resistance,
and leakage. These effects should be carefully considered to
achieve a high level of accuracy. The additional protection
circuitry is shown in Figure 5.
The performance of the circuit is highly dependent on the
sensor and the configuration of the AD7193. The Type-K
thermocouple output varies from −10 mV to +60 mV,
corresponding to −200°C to +1350°C. The AD7193 PGA is
configured for G = 32. The voltage swing out of the PGA is
−320 mV to +1.92 V, or 2.24 V p-p. With chop enabled,
50 Hz/60Hz noise reduction enabled, and filter word FS[9:0] =
96, the noise distribution histogram for 1024 samples is shown
in Figure 6.
+5V
110
5.6V ZENER DIODE
NZH5V6B
100
+5V
INPUT
SCHOTTKY DIODES
BAV199LT1G
Figure 5. Transient and Overvoltage Protection Circuit
80
70
60
50
40
30
20
Leakage currents can have a significant effect on RTD
measurements so should be carefully considered. Leakage currents
can also create some error in thermocouple measurements in
the case where long thermocouple leads have significant resistance.
8388550
8388545
8388540
8388535
NUMBER OF OCCURENCES
Figure 6. Noise Distribution Histogram of CN-0287 (VDD = 5 V, VREF =
4.096 V, Differential Input, Bipolar, Input Buffer Enable, Output Data rate =
50 Hz, Gain = 32, Chop Enable, 60 Hz Rejection Enable, Sinc4)
The resolution of the AD7193 is 24 bits, or 224 = 16,777,216
codes. The full dynamic range of the AD7193 is 2 × VREF = 2 ×
4.096 V = 8.192 V. The output voltage of the thermocouple after
the PGA is only 2.24 V p-p and does not occupy all the dynamic
range of the AD7193. Therefore the range of the system is
decreased by a factor of 2.24 V/8.192V.
The noise distribution is about 40 codes peak-to-peak. The
noise-free code resolution over the 2.24 Vp-p range of
measurement is given by:
 16 , 777 , 216 2.24 V
Noise Free Resolution = log 2 
×

400
8.192 V

= 16.8 bits
Isolation
The ADuM5401 and the ADuM1280 use ADI iCoupler®
technology provide 2500 V rms isolation voltage between the
measurement side and the controller side of the circuit. The
ADuM5401 also provides the isolated power for measurement
side of the circuit. The isoPower technique used in the ADuM5401
uses high frequency switching elements to transfer power
through a transformer. Special care must be taken with the
printed circuit board (PCB) layout to meet emissions standards.
Refer to AN-0971 Application Note for board layout
recommendations.
8388530
8388510
0
10926-006
In this circuit, the PTVS30VP1UP transient voltage suppressor
(TVS) quickly clamps any transient voltages to 30 V with only
1 nA typical leakage current at 25°C. A 30 V TVS was chosen to
allow for a 30 V dc overvoltage. A 1.69 kΩ resistor followed by
low leakage BAV199LT1G Schottky diodes are used to clamp the
voltage to the 5 V power rail during transient and dc overvoltage
events. The 1.69 kΩ resistor limits the current through the
external diodes to about 15 mA during a 30 V dc overvoltage
condition. In order to ensure the power rail is able to sink this
current, a Zener diode is used to clamp the power rail to ensure
it does not exceed the absolute maximum rating of any of the
IC’s connected to the supply. The 5.6 V Zener diode (NZH5V6B) is
selected for this purpose. A 300 Ω resistor limits any further
current that could flow into the AD7193 or the ADG738.
10
8388525
+5.3V,
−0.3V
8388520
300Ω
8388515
TVS
30V, 600W
PTVS30VP1UP
+6V,
−1V
NUMBER OF OCCURENCES
1.69kΩ
10926-005
OVERVOLTAGE
UP TO 30V
90
ADC
3mA
15mA

 (6)


The full-scale temperature range of the Type-K thermocouple is
−200°C to +1350°C, or 1550°C p-p. The 16.8 bits of noise-free
code resolution therefore corresponds to 0.013°C of noise-free
temperature resolution.
Rev. C | Page 5 of 9
CN-0287
Circuit Note
Thermocouple Measurement Linearity
RTD Configuration Test Results
Figure 7 shows the approximate linearity of the type K
thermocouple system. The “cold junction” temperature is
0°C in this plot.
For a Pt100 RTD, the default ADC gain setting is G = 8, and for
a Pt1000 RTD the default gain setting is G = 1. The reference
voltage to the ADC is equal to the voltage across the 4.02 kΩ
reference resistor. The temperature coefficient of a Pt100 RTD is
approximately 0.385 Ω/°C, and at +850°C the resistance can be
as high as 400 Ω. With a 400 µA default excitation current, the
maximum RTD voltage is therefore about 160 mV. The reference
voltage to the ADC is 4.02 kΩ × 400 µA = 1.608 V. For G = 8,
the maximum RTD voltage is 160 mV × 8 = 1.28 V which is
approximately 80% of the available range.
60
50
VOLTAGE (mV)
40
30
20
For a Pt1000 RTD, the maximum resistance at +850°C is
approximately 4000 Ω. The default excitation current is 380 µA,
yielding a maximum RTD voltage of 1.52 V. The reference voltage
to the ADC is 4.02 kΩ × 380 µA = 1.53 V. A default gain setting
of G = 1 is used, and the maximum RTD voltage utilizes nearly
all of the available range.
10
–10
–500
0
1000
500
TEMPERATURE (°C)
10926-007
0
1500
Figure 7. Type K Thermocouple Temperature vs. Output Voltage with 0°C
Cold-Junction
The precision voltage for calibration as well as testing is
provided by the Fluke 5700A Calibrator high precision dc
voltage source with a resolution of 10 nV. The voltage error in
Figure 8 is within 0.2 µV of ideal, corresponding to about
0.004°C. This result is the short time accuracy result just after a
system calibration at 25°C without the effects of temperature
drift.The dominant error for this circuit is from the coldjunction compensation measurement. In this circuit the
ADT7310 is used for cold-junction compensation and has a
typical error of −0.05°C, and a worst case error of ±0.8°C over
the −40°C to +105°C temperature range for a 5 V supply. The
device has a ±0.4°C maximum error over this temperature
range if a 3 V supply is used.
0.20
The general expression for the RTD resistance, R, in terms of
the ADC code (Code), resolution (N), reference resistor (RREF),
and gain (G) is given by:
R=




The total leakage current for each of the inputs is 9 nA (3 nA from
AD7193, buffer on), 5 nA from clamping diode and 1 nA from
the TVS diode). All four channels will thus generate 36 nA
maximum leakage current. The feedback loop in Figure 2 maintains
a constant current through the reference resistor. This means
that leakage currents affect the RTD excitation current, thereby
producing an error. The default exciting current is 400 µA for
Pt100 and 380 µA for Pt1000. The approximate worst case system
error due to the leakage currents for Pt100 RTDs is:
 36 nA
Error(%) = 
 400 μA

0.10
(7)
The leakage current from TVS, diodes, clamping diodes, and
ADC are the largest sources of errors in the RTD measurement
circuit, even though nanoamp devices were selected for the design.
0.15
VOLTAGE ERROR (µV)
Code  R REF


2N  G

 × 100 ≈ 0.01% of reading


(8)
For a Pt100 with measurable range from −200°C to +850°C, this
corresponds to a system accuracy of approximately
0.05
0
1
6
11
16
21
26
31
36
INPUT VOLTAGE (mV)
41
46
51
10926-008
Accuracy ( C  ) =
Figure 8. Error of CN-0287 Configured for Type K Thermocouple (VDD = 5 V,
VREF = 4.096 V, Differential Input, Bipolar, Input Buffer Enable, Output Data
Rate = 50 Hz, Gain = 32, Chop Enable. 60 Hz Rejection Enable, Sinc4)
400 Ω
0.385 Ω / C

× 0.0001 ≈ 0.1 C 
(9)
The amount of the error depends on the configuration of the
input terminals. After an input configuration is established, a
room temperature calibration can reduce the error even further.
An experiment was conducted to show the effects of leakage
current. Each channel was first configured as a 4-W RTD. A
100 Ω fixed resistor was connected to Channel 1 in the RTD
position. Zero ohm resistors were connected to the inputs of the
other three channels.
Rev. C | Page 6 of 9
Circuit Note
CN-0287
The gain was set for G = 1, and the excitation current for
380 µA (Pt1000 configuration).
•
•
Data was collected, then the jumpers connecting Channel 4,
Channel 3, and Channel 2 were removed sequentially, and data
collected for each condition. The results are shown in Figure 9.
•
437860
437840
437820
Getting Started
437800
Install the evaluation software by placing the CN-0287
Evaluation Software into the CD drive of the PC. Using My
Computer, locate the drive that contains the evaluation software.
437780
437760
437740
437720
The CN-0287 SDP Evaluation Software
The EVAL-CFTL-6V-PWRZ dc power supply or
equivalent 6 V/1 A bench supply
A RTD or thermocouple sensor or sensor simulator.
(The evaluation software supports the following
RTDs: Pt100, Pt1000; Thermocouple: Type K, Type J,
Type T, Type S.)
ALL
LEAKAGE
INCLUDED
437700
Functional Block Diagram
LEAKAGE
FROM CH4
REMOVED
437680
See Figure 1 for the circuit block diagram and the EVALCN0287-SDPZ-PADSSchematic.pdf file for the complete circuit
schematic. This file is contained in the CN0287 Design Support
Package located at www.analog.com/CN0287-DesignSupport A
functional block diagram of the test setup is shown in Figure 10.
437660
437640
437600
LEAKAGE
FROM CH2
REMOVED
437580
10926-009
LEAKAGE
FROM CH3
REMOVED
437620
Figure 9. Error Generated by Leakage Current on Channel 1 for 4-Channel
Pt100 RTD with G = 1
EVAL-CFTL-6V-PWRZ
6V WALL WART
The ADC code changed from approximately 437,800 to 437,600
corresponding to a measurement change of 104.9015 Ω to
104.8627, or 0.0388 Ω. This represents a measurement error of
approximately 0.1°C; however it can be removed by calibrating
at room temperature with a fixed input configuration.
USB CABLE
SENSORS
CIRCUIT EVALUATION AND TEST
This circuit uses the EVAL-CN0287-SDPZ circuit board and the
SDP-B (EVAL-SDP-CB1Z) system demonstration platform
controller board. The two boards have 120-pin mating
connectors, allowing for the quick setup and evaluation of the
performance of the circuit. The EVAL-CN0287-SDPZ board
contains the circuit to be evaluated, as described in this note,
and the SDP-B controller board is used with the CN-0287
Evaluation Software to capture the data from the EVALCN0287-SDPZ circuit board.
Equipment Needed
The following equipment is needed:
•
•
•
1.000V
120
PINS
EVAL-SDP-CB1Z
SDP BOARD
(x) = 1, 2, 3, 4
EVAL-CN0287-SDPZ
BOARD
10926-010
OR
SIGNAL
GENERATORS
SDP
CONNECTOR
JP(x)
RMS isolation up to 5 kV is be available in the ADuM6401
digital isolator with dc-to-dc converter.
USB
CN5 OR J2
CN(x)
COMMON VARIATIONS
The AD779x low noise, low power, 16-/24-bit sigma-delta
ADC family is more suitable for single channel or low power
applications. The ADT7311, ±0.5°C accurate, 16-bit digital SPI
temperature sensor is qualified for automotive applications. The
cold junction compensation circuit accuracy can be improved
by using a digital temperature sensor, such as ADT7320, with
±0.25°C accuracy.
PC
Figure 10. Test Setup Functional Block Diagram
Setup
Connect the 120-pin connector on the EVAL-CN0287-SDPZ
circuit board to the CON A connector on the EVAL-SDP-CB1Z
controller board (SDP-B). Use nylon hardware to firmly secure
the two boards, using the holes provided at the ends of the 120-pin
connectors. With power to the supply off, connect a 6 V power
supply to the +6 V and GND pins on the board. If available, a 6 V
wall wart can be connected to the barrel connector J2 on the
board and used in place of the 6 V power supply. Connect the
USB cable supplied with the SDP-B board to the USB port on
the PC. Do not connect the USB cable to the Mini-USB connector
on the SDP-B board at this time.
Turn on the 6 V power supply to power up the evaluation board
and SDP board, then plug in the Mini-USB cable into the MiniUSB port on the SDP board.
A PC with a USB port and Windows® XP (32 bit),
Windows Vista®, or Windows® 7
The EVAL-CN0287-SDPZ circuit board
The EVAL-SDP-CB1Z SDP-B controller board
Rev. C | Page 7 of 9
CN-0287
Circuit Note
Test
Connectivity for Prototype Development
Launch the evaluation software. After USB communications are
established, the SDP-B board can be used to send, receive, and
capture data from the EVAL-CN0287-SDPZ board.
The EVAL-CN0287-SDPZ evaluation board is designed to use
the EVAL-SDP-CB1Z SDP-B board; however, any
microprocessor can be used to interface to the SPI interface
through the PMOD connector J6. The pin definition of PMOD
connector can be found in the schematics of CN0287 evaluation
board in CN-0287 Design Support Package. In order for
another controller to be used with the EVAL-CN0287-SDPZ
evaluation board, software must be developed by a third party.
Figure 11 shows a photo of the EVAL-CN0287-SDPZ evaluation
board connected to the SDP board. Information regarding the
SDP-B board can be found in the SDP-B User Guide.
10926-011
Information and details regarding test setup and calibration,
and how to use the evaluation software for data capture can be
found in the CN-0287 Software User Guide.
Figure 11. EVAL-CN0287-SDPZ Evaluation Board Connected to the EVAL-SDP-CB1Z SDP-B Board
Rev. C | Page 8 of 9
CN-0287
Circuit Note
LEARN MORE
Data Sheets and Evaluation Boards
CN-0287 Design Support Package:
www.analog.com/CN0287-DesignSupport
CN-0287 Circuit Evaluation Board (EVAL-CN0287-SDPZ)
System Demonstration Platform (EVAL-SDP-CB1Z)
SDP-B User Guide
AD7193 Datasheet
AN-880 Application Note, ADC Requirements for Temperature
Measurement, Analog Devices.
AD8603 Datasheet
AN-892 Application Note, Temperature Measurement Theory
and Practical Techniques, Analog Devices.
ADG702 Datasheet
AN-0970 Application Note, RTD Interfacing and Linearization
Using an ADuC706x Microcontroller, Analog Devices.
ADG738 Datasheet
ADT7310 Datasheet
ADuM5401 Datasheet
CN-0172, High Accuracy Multichannel Thermocouple
Measurement Solution, Analog Devices.
ADuM1280 Datasheet
CN-0206, Complete Type T Thermocouple Measurement System
with Cold Junction Compensation, Analog Devices.
ADR3440 Datasheet
AD5201 Datasheet
CN-0209, Fully Programmable Universal Analog Front End for
Process Control Applications, Analog Devices.
CN-0221, USB-Based Temperature Monitor Using the
ADuCM360 Precision Analog Microcontroller and an
External Thermocouple, Analog Devices.
REVISION HISTORY
2/14—Rev. B to Rev. C
Change to Common Variations Section ........................................ 7
9/13—Rev. A to Rev. B
Changes to Figure 1 .......................................................................... 1
CN-0271, K-Type Thermocouple Measurement System with
Integrated Cold Junction Compensation, Analog Devices.
Kester, Walt. 1999. Sensor Signal Conditioning. Analog Devices.
Chapter 7, "Temperature Sensors."
Matthew Duff and Joseph Towey. Two Ways to Measure
Temperature Using Thermocouples Feature Simplicity,
Accuracy, and Flexibility, Analog Dialogue 44-10, Analog
Devices.
8/13—Rev. 0 to Rev. A
Changes to Title ................................................................................. 1
8/13—Revision 0: Initial Version
Mary McCarthy, AN-615 Application Note, Peak-to-Peak
Resolution Versus Effective Resolution.
MT-049 Tutorial, Op Amp Total Output Noise Calculations for
Single-Pole System. Analog Devices.
MT-004 Tutorial, The Good, the Bad, and the Ugly Aspects of
ADC Input Noise—Is No Noise Good Noise? Analog
Devices.
MT-031 Tutorial, Grounding Data Converters and Solving the
Mystery of “AGND” and “DGND”, Analog Devices.
MT-035, Op Amp Inputs, Outputs, Single-Supply, and Rail-toRail Issues, Analog Devices.
MT-101 Tutorial, Decoupling Techniques, Analog Devices.
(Continued from first page) Circuits from the Lab reference designs are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors.
While you may use the Circuits from the Lab reference designs in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual
property by application or use of the Circuits from the Lab reference designs. Information furnished by Analog Devices is believed to be accurate and reliable. However, Circuits from the
Lab reference designs are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability,
noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties
that may result from their use. Analog Devices reserves the right to change any Circuits from the Lab reference designs at any time without notice but is under no obligation to do so.
©2013–2014 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
CN10926-0-2/14(C)
Rev. C | Page 9 of 9
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