CN-0267 [ADI]

Complete 4 mA to 20 mA Loop Powered Field Instrument with HART Interface; 完整4 mA至20 mA环路供电现场仪器具有HART接口


型号：	CN-0267
厂家：	ADI
描述：	Complete 4 mA to 20 mA Loop Powered Field Instrument with HART Interface 完整4 mA至20 mA环路供电现场仪器具有HART接口
文件：	总8页 (文件大小：407K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

Circuit Note

CN-0267

Devices Connected/Referenced

Low Power, Precision Analog

Microcontroller

ADuCM360

Circuits from the Lab™ reference circuits 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/CN0267.

16-Bit, Loop Powered, 4 mA to 20 mA

DAC

AD5421

AD5700

Low Power HART Modem

Complete 4 mA to 20 mA Loop Powered Field Instrument with HART Interface

features such as remote calibration, fault interrogation, and

transmission of process variables, which are necessary in

applications such as temperature and pressure control.

EVALUATION AND DESIGN SUPPORT

Circuit Evaluation Board

CN0267 Circuit Evaluation Board (DEMO-AD5700D2Z)

Design and Integration Files

This circuit has been compliance tested, verified, and registered by

the HART Communication Foundation (HCF). This successful

registration provides circuit designers with a high level of

confidence using one or all of the components in the circuit.

Schematics, Layout Files, Bill of Materials, Code Example

CIRCUIT FUNCTION AND BENEFITS

The circuit shown in Figure 1 is a complete smart industrial,

loop powered field instrument with 4 mA to 20 mA analog output

and a highway addressable remote transducer (HART®) interface.

HART is a digital 2-way communication in which a 1 mA peak-

to-peak frequency-shift-keyed (FSK) signal is modulated on top

of the standard 4 mA to 20 mA analog current signal. This allows

The circuit uses the ADuCM360, an ultralow power, precision

analog microcontroller, the AD5421, a 16-bit, 4 mA to 20 mA,

loop powered digital-to-analog converter (DAC), and the AD5700,

the industry’s lowest power and smallest footprint HART-

compliant IC modem.

AD5421

LOOP+

REG

1.6Ω

10µF

10Ω

OUT

VOLTAGE

REGULATOR

10µF

PRIMARY

SENSOR

20MΩ

1MΩ

LOOP

DVDD

IOVDD

ADuCM360

4700pF

ADC

10µF

TEMPERATURE

SENSOR

AVDD

VREF+

REFOUT1

REFOUT2

VREF

TVS

40V

0.01µF

0.1µF

10µF

AIN0

AIN1

1kΩ

LOW

DAC

ADC0

LEAKAGE

1kΩ

SPI INTERFACE

CS0

SYNC

SCLK

SDIN

SDO

COM

0.01µF

SCLK0

MOSI0

MISO0

WATCHDOG

TIMER

CORTEX

50Ω

VREF–

LOOP–

SRAM

FLASH

LDAC

GND_SW

AVDD_

REG

0.47µF

DVDD

4.7V

LOW LEAKAGE

DMA

UART

SPI

SECONDARY

SENSOR

AVDD

470Ω

1µF

DVDD_

REG

EXC

AIN4

I C

1kΩ

0.47µF

CLOCK

RESET

WATCHDOG

AD5700

0.068µF

0.1µF

HART_OUT

0.22µF

0.01µF

0.1µF

XTAL1

1kΩ

AIN3

AIN2

3.8664MHz

ADC1

REF

XTAL2

TXD

RXD

1kΩ

PT100

RREF

UART INTERFACE

1µF

1.2MΩ

SOUT

SIN

P0.5

P0.4

0.01µF

300pF

150kΩ

ADC_IP

VREF

AIN7

RTS

REG_CAP

1.2MΩ

150pF

EXPOSED

PAD

0.1µF

DGND

AGND

5.62kΩ

AGND

10ppm

AGND

DGND

NOTES

1. L* = FERRITE BEAD, 0.3Ω @ DC, 1kΩ @ 100MHz.

2. THE ADuCM360 EXPOSED PAD IS CONNECTED TO DGND.

Figure 1. 4 mA to 20 mA, Loop Powered Field Instrument with HART Interface (Simplified Schematic: All Connections and Decoupling Not Shown)

Rev. A

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CN-0267

Circuit Note

Digital Data Processing, Algorithm, and Communications

CIRCUIT DESCRIPTION

All the field instrument digital functions are provided by the

ADuCM360 32-bit ARM Cortex™ M3 RISC processor, with

integrated 128 k bytes of nonvolatile flash/EE memory, 8 k bytes

of SRAM, and an 11-channel direct memory access (DMA)

controller that supports wired (2× SPI, UART, I²C) communication

peripherals.

Analog Front-End Interface

The ADuCM360 analog front-end incorporates dual, high

performance 24-bit sigma-delta (Σ-Δ) analog-to-digital converters

(ADCs). It also integrates programmable gain instrumentation

amplifiers, a precision band-gap reference, programmable current

sources, a flexible multiplexer, and many other features. It allows a

direct interface to multiple analog sensors, such as pressure

sensor bridges, resistive temperature sensors, thermocouples,

and many other types of sensors used in the industry.

The demonstration software performs the initialization and

configuration, processes data from the analog inputs, controls

the analog output, and performs the HART communication.

The circuit in Figure 1 shows an example connection for a primary

bridge type sensor and a secondary resistive temperature sensor;

however the ADuCM360 flexible front-end allows many other

configurations to accommodate any type of precision analog

sensor application.

Analog Output

The AD5421 integrates a low power precision 16-bit DAC with

a 4 mA to 20 mA, loop powered output driver and provides all

functions required for the field instrument analog output.

The AD5421 interfaces with the ADuCM360 controller via the

SPI interface.

Primary Sensor Input

The ADuCM360 on-chip ADC0 measures the field instrument

primary sensor, shown as a bridge transducer in Figure 1. The

sensor connects to the analog input pins, AIN0 and AIN1, via an

RC filter network for improved system electromagnetic immunity.

The common-mode filter bandwidth is approximately 16 kHz,

and the differential-mode bandwidth is 800 Hz.

The AD5421 also includes a range of diagnostic functions

related to the 4 mA to 20 mA loop. The auxiliary ADC can

measure the voltage across the instruments loop terminals via

the 20 MΩ/1 MΩ resistive divider connected to the V_LOOPpin.

The ADC can also measure the chip temperature via the integrated

sensor. The ADuCM360 controller can configure and read all

the diagnostics of the AD5421, but the AD5421 can also operate

autonomously.

The ADuCM360 VREF+ and VREF− voltage reference inputs

sense the bridge excitation voltage and enable the circuit to work in

a ratiometric mode, making the measurement independent of

the exact value of the sensor power supply voltage. The on-chip

ground switch can dynamically disconnect the bridge excitation

and save power when required by the application.

As an example, if the communication between the controller and

the AD5421 fails, the AD5421 automatically sets its analog

output to a 3.2 mA alarm current after a defined period. This

alarm current indicates to the host that the field instrument

failed to operate.

Secondary Sensor Input

The circuit uses a platinum (Pt) 100 Ω resistive temperature

device (RTD) as a secondary sensor. The RTD can sense the

temperature of the primary sensor and thus allow for temperature

compensation of the primary sensor if required.

The software controls any change of the output current from

one value to another to prevent disturbance of the HART

communication. (See the Analog Rate of Change section).

HART Communication

The ADuCM360 programmable current source supplies the RTD

via the AIN4 pin. The ADC1 on the ADuCM360 measures the

voltage across the RTD using the AIN3 and AIN2 pins configured

as a differential input. The exact value of the current flowing

through the RTD is sensed by a precision resistor (RREF) and is

measured by the ADC1 using the AIN7 pin. The ADC1 uses the

on-chip, band-gap voltage reference.

The AD5700 integrates a complete HART FSK modem. The

modem is connected to the ADuCM360 controller via a standard

UART interface, complemented by request to send (RTS) and

carrier detect (CD) signals.

The HART output is scaled to the required amplitude by the

0.068 µF/0.22 µF capacitive divider and coupled to the AD5421

_INpin, where it is combined with the DAC output to drive and

modulate the output current.

The HART input is coupled from LOOP+ via a simple passive

RC filter to the AD5700 ADC_IP pin. The RC filter works as

the first stage, band-pass filter for the HART demodulator and

also improves the system electromagnetic immunity, which is

important for robust applications working in harsh industrial

environments.

The AD5700 low power oscillator generates the clock for the

HART modem with a 3.8664 MHz external crystal connected

directly to the XTAL1 and XTAL2 pins.

Rev. A | Page 2 of 8

Circuit Note

CN-0267

Output Protection

The AD5700 HART modem is supplied through an additional

RC filter (470 Ω/1 µF). This filter is very important in the loop

powered application because it prevents current noise from the

AD5700 from coupling to the 4 mA to 20 mA loop output, which

would otherwise affect the HART communication. The 4 mA to

20 mA loop noise performance is specifically addressed by the

HART in-band, noise during silence test. The AD5700 modem

uses the external crystal with 8.2 pF capacitors to ground on the

XTAL1 and XTAL2 pins, which is the option using the least

possible power.

A transient voltage suppressor (TVS) protects the 4 mA to 20 mA

HART interface from overvoltage. Its voltage rating should prevent

exceeding the AD5421 absolute maximum voltage of 60 V on

the REG_INpin. Note that the TVS leakage current can affect the

current output accuracy; therefore, pay attention to the leakage

current at a given loop voltage and temperature range when

selecting this component.

An external depletion-mode FET can be used with the AD5421

to increase the loop voltage maximum

The ADuCM360 has very flexible internal power management,

with many options for powering and clocking all the internal

blocks and, when utilized by the software, allows an optimal

balance between the required function, performance, and power

for the specific instrument application. Refer to the ADuCM360

product page and the AN-1111 Application Note.

The circuit is protected against reversed polarity by a pair of

diodes in series with loop output.

The ferrite beads in series with the loop together with the 4700 pF

capacitor improve the system EMC performance. Do not use a

higher capacitance across the loop terminals because of the HART

network specifications.

The analog front-end AVDD is supplied from another filter

(10 µF/ferrite bead/1.6 Ω/10 µF) to minimize power supply noise

for better performance with respect to low voltage sensor signals.

The 4.7 V, low leakage, Zener diode protects the AD5421 on-chip,

50 Ω loop sense resistor in the event of an accidental external

voltage between the AD5421 COM pin and LOOP− pin (for

example, when programming the ADuCM360 or debugging

the circuit).

The GND_SW ground switch pin of the ADuCM360 controls

the excitation/power supply for the primary sensor. The switch

is off as a default at the instrument power up. This default allows

the system to be fully configured, including appropriate power

modes, before turning on the sensor, and thus minimizes any

possible power-up spikes on the 4 mA to 20 mA loop output.

Power Supplies and Power Management

The complete field instrument circuitry, including the sensor drive

current, must operate on the limited amount of power available

from the 4 mA to 20 mA loop. This is a common challenge in

any loop powered field instrument design. The circuit in Figure 1

provides an example of delivering both a low power and high

performance solution. All three integrated circuits used in the

application are designed for low power, and the circuit leverages

their integrated features to deliver a flexible power management

structure and an optimum loop-powered solution.

Similarly, the secondary sensor is supplied from the programmable

current source of the ADuCM360, and therefore, its power is

fully controlled by the software.

ADuCM360 Software

A basic code example that demonstrates the functionality and

performance of the circuit can be found in the CN-0267 Design

Support Package.

The AD5421 is powered by the 4 mA to 20 mA loop voltage and

provides a regulated low voltage for the rest of the circuit. The

AD5421 REG_OUTvoltage is pin programmable from 1.8 V to 12 V

depending on circuit requirements. The circuit in Figure 1 uses

the 3.3 V supply voltage option as an example for the input sensors

used. However, the ADuCM360 and the AD5700 have a wider

power supply voltage range; therefore, a different power supply

voltage can be used to suit the application.

The code example includes a basic HART slave command response

to demonstrate the hardware function and capability. However,

the code example does not include the protocol layers of the

HART communication.

COMMON VARIATIONS

The ADuCM360 has a high performance and very flexible analog

front-end, with 12 analog input pins and extra pins for voltage

reference and ground switch. It allows direct interface to multiple

analog sensors of varying types, such as any resistive bridge sensors,

resistive temperature sensors, or thermocouples. Therefore, do

not limit the field instrument solution to temperature-compensated

pressure measurement only because it can be used for almost any

sensor field instrument.

The REG_OUTRC filter (10 µF/10 Ω/10 µF) helps to prevent any

interference coming from the loop affecting the sensor analog

front-end. It also prevents any interference generated by the

circuit, specifically by the controller and the digital circuitry,

from coupling back to the loop, which is important for a reliable

HART communication.

The ADuCM361 can be used as an alternative to the ADuCM360

in applications that need only one Σ-Δ ADC in the analog front-

end. Aside from the second ADC, the ADuCM361 contains all

the features of the ADuCM360.

Rev. A | Page 3 of 8

CN-0267

Circuit Note

The ADuCM361 on-chip DAC with an external transistor can

be used to control the 4 mA to 20 mA loop, refer to CN-0300

for details.

CIRCUIT EVALUATION AND TEST

Circuit Hardware

The circuit shown in Figure 1 is built on the DEMO-AD5700D2Z

printed circuit board shown in Figure 3.

The AD5421 can be connected via the protection directly to the

loop. Alternatively, a depletion mode N-channel MOSFET can

be connected between the AD5421 and the loop power supply,

as shown in Figure 2. The use of the additional MOSEFT in

this configuration keeps the voltage drop across the AD5421 at

approximately 12 V, lowers the power dissipated in the AD5421

package, and therefore improves the 4 mA to 20 mA analog output

accuracy. It also increases the maximum voltage allowed in the

loop to the level of the MOSFET rating. The additional MOSFET

has no effect on the HART communication.

LOOP+

Figure 3. DEMO-AD5700D2Z Printed Circuit Board (Pressure Sensor Not Included)

DN2540

BSP129

The DEMO-AD5700D2Z circuit board includes some additional

features for easy system evaluation. The 0.1 inch-pitch connector

footprints allow optional primary and secondary sensor

connections. There are test points for HART RTS and CD

that may be needed for HART compliance tests.

AD5421

200kΩ

4700pF

REG

DRIVE

TVS

40V

LOW

20MΩ

1MΩ

A connector on the edge of the DEMO-AD5700D2Z makes the

ADuCM360 single wire and UART download/debug signals

accessible allowing easy software development, code download,

and in-circuit debugging and emulation. The connector, with a

small header extender included with the DEMO-AD5700D2Z

board, is compatible with all Analog Devices, Inc., Cortex-M3

based development tools, such as the EVAL-ADuCM360QSPZ

evaluation kit (the evaluation kit is not included with the

DEMO-AD5700D2Z board).

LEAKAGE

LOOP

COM

LOOP–

4.7V

LOW

LEAKAGE

HART

INPUT

FILTER

Figure 2. MOSEFT Connected to the AD5421 Loop Power Supply

These features are not shown in the simplified diagram in Figure 1;

however, they can be seen in the complete circuit schematic in

the CN-0267 Design Support Package. The design support package

also includes a full field instrument C-code example, which

enables complete verification and evaluation of all hardware

blocks and features of the circuit, and a limited verification of

the HART interface functionality. For detailed information about

HART interface specifications and resources, contact the Hart

Communication Foundation.

The AD5700 is used with a 3.8664 MHz crystal in this circuit,

which is the configuration achieving the lowest power consumption.

Alternatively, the AD5700-1, with an integrated 0.5 %precision

internal oscillator, can be used. The internal oscillator increases

the modem power supply current by 225 µA maximum, compared

to the crystal oscillator, but because no external crystal is needed,

this option provides both cost savings and reduced board area

requirements.

For the applications that are not loop powered, the AD5410,

AD5420, AD5422, or AD5755 are good choices for the 4 mA to

20 mA DAC.

HART Compliance

The DEMO-AD5700D2Z has been verified to be compliant with

HART FSK Physical Layer Specification (HCF_SPEC-054,

Revision 8.1), using methods and equipment specified in the

HART Physical Layer Test Specification (HCF_TEST-2,

Revision 2.2). The board was submitted to the Hart

Communication Foundation and was successfully registered.

The registered circuit can be found on the HART Communication

Foundation (HFC) web site in the product catalog as DEMO-

AD5700D2Z.

The results of two of the tests involved the output noise during

silence and the analog rate of change.

Rev. A | Page 4 of 8

Circuit Note

CN-0267

Output Noise During Silence Test

The hardware slew-rate limit is set by the capacitance connected

to the AD5421 C_INpin. When a large step change is required in

the analog output current value, the ADuCM360 software splits

the output current change sent to the AD5421 DAC into a number

of smaller subsequent steps.

When a HART device is not transmitting (silence), do not couple

noise onto the network. Excessive noise may interfere with

reception of HART signals by the device itself or other devices

on the network.

This test was performed using an oscilloscope coupled to the

500 Ω load through the HCF_TOOL-31 filter.

The voltage noise measured across a 500 Ω load in the loop must

contain no more than 2.2 mV rms of combined broadband and

correlated noise in the HART extended frequency band. In

addition, the noise should not exceed 138 mV rms outside the

HART extended frequency band.

The result is shown in Figure 5. Waveform CH1 shows the periodic

steps between 4 mA and 20 mA, sensed directly across the 500 Ω

load. Waveform CH2 is the signal captured on the HCF_TOOL-31

filter output, amplified 10×, within the 150 mV peak limits.

This noise was measured by a true rms meter across the 500 Ω

load. This noise was measured directly for the out-of-band noise

and measured through the HCF_TOOL-31 filter for the in-band

noise. An oscilloscope was also used to examine the noise

waveform.

MEASURE

CH1

p-p

8.60V

CH1

4mA TO 20mA

ACROSS 500Ω

CH1

FREQ

8.123Hz?

The noise was measured at the worse condition, which was 4 mA

output current. The captured noise waveform is shown in

Figure 4, and the results are summarized in Table 1.

MEASURE

CH2

OUTPUT OF

FILTER × 10

CH2

p-p

254mV

CH1

p-p

44.8mV

CH2

MAX

134mV

LIMIT =

±150mV

CH1

CYC RMS

4.64mV?

CH2

MIN

–120mV

CH1

CH1 5.00V CH2 50mV

M 25.0ms

CH1

6.80V

NONE

Figure 5. Analog Rate of Change Waveform

CH1

NONE

Circuit Power Consumption

Two methods were used to evaluate the circuit power consumption

performance.

CH2

OFF

NONE

In the first method, the current from the AD5421 integrated

voltage regulator output was measured.

CH1 20.0mV

M 100ms

CH1

<10Hz

–8.00mV

Figure 4. Output Noise During Silence Waveform

Considering the minimum analog output current of 4 mA and

HART output ac modulation of 0.5 mA peak, the maximum

current consumed by the circuit in normal mode operation must

be less than 3.5 mA. The AD5421 requires a 0.3 mA maximum

for its own operation, which leaves approximately 3.2 mA

maximum current for the AD5421 REG_OUToutput.

Table 1. Output Noise During Silence

Measured Required

Output Noise

(mV)

<138

<2.2

Outside Extended Frequency Range 4.13

Inside Extended Frequency Range

1.03

For ease of in-circuit measurement, the DEMO-AD5700D2Z

has test points (T5, T6) on each side of the 10 Ω resistor in the

REG_OUToutput filter, as shown in Figure 6. This setup allows the

voltage drop across the resistor to be measured, and the current

to be calculated without interrupting the supply current or

disturbing the circuit.

Analog Rate of Change Test

This specification ensures that when a device regulates the

analog output current, the maximum rate of change of analog

current does not interfere with HART communications. Step

changes in current disrupt HART signaling.

VOLTMETER

The worst-case change in the analog output current must not

produce a disturbance higher than 15 mV peak, measured

across a 500 Ω load in the HART extended frequency band.

AD5421

REG

10Ω

OUT

REST OF CIRCUIT

POWER SUPPLY

VOLTAGE

REGULATOR

The AD5421 DAC and output driver are relatively fast. Therefore,

to meet the required system specification, the output current

change is controlled by combining hardware slew-rate limiting

implemented at the AD5421 and a digital filter implemented in

the ADuCM360 software.

10µF

Figure 6. Measuring the AD5421 REG_OUTCurrent Using Test Points

Rev. A | Page 5 of 8

CN-0267

Circuit Note

The results are shown in Table 2 and were measured at the

following conditions:

The demonstration was configured to transmit data from the

primary analog input, expressed as pressure in kPa, over the

HART communication. One hundred samples were captured,

and a basic data analysis to quantify the performance was

completed. Two of the tests involved the following:

•

REG_OUT= 3.3 V

ADuCM360 M3 core clock = 2 MHz

Both ADCs converting at 50 samples per second

ADC0 has both buffers on and gain = 8

ADC1 has both buffers on and gain = 16

RTD excitation current = 200 µA

•

The first test was performed with a standard pressure sensor

(Honeywell 24PCDFA6D) soldered directly on the board.

A second test was performed with the primary input signal

generated by a set of fixed and variable resistors, as shown

in Figure 7.

•

SPI communicating to AD5421 with serial clock = 100 kHz

HART communicating

The circuit with all relevant analog and digital blocks, including

the input sensor, consumes power supply current within the

budget allowed at the minimum 4 mA loop current.

AVDD

ADuCM360

VREF+

27kΩ

10kΩ

Table 2. Power Supply Current from AD5421, REG_OUT= 3.3V

0.01µF

0.1µF

AIN0

AIN1

1kΩ

Voltage T5 to T6

Maximum (mV)

Current REG_OUT

Maximum (mA)

ADC0

Input Sensor

None

24PCDFA6D (5 kΩ,

0.66 mA at 3.3 V)

24.4

31.0

2.44

3.10

0.01µF

18kΩ

VREF–

In the second method for assessing the circuit power consumption,

the circuit was verified to function as expected with the analog

output current set to the minimum of 4 mA while performing

HART communication. The result showed that the circuit

delivered the 4 mA current and showed no distortion of the

HART output signal.

GND_SW

Figure 7. Primary Input Signal Generated by a Set of Resistors

Primary Sensor Input Performance

The ADuCM360 integrates most of the analog front-end on chip;

therefore, the performance of the analog input is primarily

determined by the specifications of the ADuCM360.

The level of noise is the main factor that can be influenced by

the interaction of the analog front-end with the rest of the

circuitry on the board. Thus, tests were carried out to focus on

the noise and related resolution performance of the system.

Rev. A | Page 6 of 8

Circuit Note

CN-0267

The performance summary can be seen in Table 3, and the

signal plots are shown in Figure 8 and Figure 9.

Secondary Sensor Input Performance

Similar to the primary sensor, the performance of the secondary

sensor input is mainly determined by the analog front-end of

the ADuCM360 with the exception of noise performance.

Table 3. Primary Sensor Input Noise and Resolution

Pressure

Sensor

Resistive

Parameter

Network

246 kPa

0.68 Pa

3.6 Pa

18.5 bit

16.1 bit

The analog input was configured to transmit temperature in

degrees Celsius (°C) to a master over the HART communication

path. Analysis was performed on two tests of 100 samples to

quantify the performance.

Full Scale

Noise RMS

Peak-to-Peak Noise

Resolution Effective (rms)

Noise-Free Resolution (p-p)

207 kPa

1.3 Pa

6.8 Pa

17.2 bit

14.9 bit

The first test was performed using the platinum 100 Ω sensor

on the board, and the second test was performed with the sensor

replaced on the board by a standard (fixed) 100 Ω 1% resistor.

The performance summary is shown in Table 4, and the signal

plots are shown in Figure 10 and Figure 11.

Table 4. Secondary Sensor Input Noise Performance

Parameter

Pressure Sensor

Resistive Network

Noise RMS

0.037°C

0.033°C

0.16°C

Noise Peak to Peak

0.19°C

25.0

24.5

24.0

23.5

23.0

100

SAMPLE

Figure 8. Pressure Sensor Input Signal Plot

100

SAMPLE

Figure 10. RTD (Platinum 100 Ω) Sensor Input Signal Plot

1.0

–5

–10

0.5

0.0

100

SAMPLE

Figure 9. Resistive Network as Primary Input Signal Plot

–0.5

–1.0

100

SAMPLE

Figure 11. Fixed 100 Ω 1% Resistor as the Secondary Input Signal Plot

Rev. A | Page 7 of 8

CN-0267

Circuit Note

Data Sheets and Evaluation Boards

LEARN MORE

ADuCM360 Data Sheet and Evaluation Board

AD5421 Data Sheet and Evaluation Boards

AD5700 Data Sheet and Evaluation Board

REVISION HISTORY

CN-0267 Design Support Package:

http://www.analog.com/CN0267-DesignSupport

CN-0270, Complete 4 mA to 20 mA HART Solution

CN-0278, Complete 4 mA to 20 mA HART Solution with

Additional Voltage Output Capability

2/13—Rev. 0 to Rev. A

Changes to Circuit Hardware Section and Figure 3 Caption ......4

CN-0300, Complete Closed-Loop Precision Analog

Microcontroller Thermocouple Measurement System with

4 mA to 20 mA Output

12/12—Revision 0: Initial Version

AN-1111, Options for Minimizing Power Consumption When

Using the ADuCM360/ADuCM361

HART® Communication Foundation

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reserves the right to change any Circuits from the Lab circuits at any time without notice but is under no obligation to do so.

registered trademarks are the property of their respective owners.

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